Introduction: 

An alteration in an atom’s energy is known as electron affinity. An atom gains a negative charge and releases energy as more electrons are added to its outer shell. In order to stabilise its octet, an element obtains electrons. When an element receives or loses an electron, energy is released. An exothermic reaction occurs when an element takes an electron to form a compound, releasing energy in the process. An exothermic process releases energy because a nucleus from another element is using it to attract the electron. An endothermic process is one in which energy is absorbed when an element loses an electron. An atom gets energy when one or more of its electrons are lost.

What is electron Affinity?

A molecule either loses or gains energy during a chemical reaction. Energy is gained or lost as electrons are gained or lost. Exothermic reactions occur when an atom loses an electron, releasing energy. Chemical reactions in which electrons are lost are called endothermic because they consume energy. The ability to accept an electron is referred to as the electron’s affinity. when a neutral gaseous atom accepts the electron, it will charge with a negative ion. There is always a negative value for the first electron affinity and a positive value for the second. Atomic electron affinity measurements are notoriously imprecise. Ionic compounds’ energy dissipation is used as a proxy for this. The propensity of an atom to act as an oxidising or reducing agent is another indicator of its electron affinity. Kilojoules per mole is the unit of measure. Ea represents the attraction between electrons.

First Electron Affinity: 

When an electron is added to an atom that is electrically neutral, the atom gains a negative charge and releases energy. Since greater energy is needed to draw an electron via the nucleus, the initial electron affinity is usually negative. 

The common trends followed in the periodic table are: 

• When one moves down the periodic table, electron affinity decreases.
• The electron affinity rises as we progress from left to right over the time.
• When metals lose an electron, they become cations.
• When a nonmetal accepts an electron, it forms an anion. 
• Due to the ease with which they may lose an electron from their outer shell, metals have a lower electron affinity than nonmetals.
• It is an endothermic process for metals to lose one electron because the outer shell electrons have less attraction. An Element of Matter

Electron Affinity of atom

Second Electron Affinity:

Gaining an electron is the anion’s second electron affinity. Second electron affinity manifests itself in the group-16 elements oxygen, sulphur, and selenium because these elements form anions with (-2) ions.

For example: 

The electron affinity of oxygen is given as;

The second electron affinity is higher than the first electron affinity in oxygen molecules because of the electron-electron repulsion in the negatively charged ion of oxygen. 

Factors Affecting Electron Affinity:

The electrical arrangement of atoms, the nuclear charge of the molecules, and the atomic size all play a role in determining a molecule’s electron affinity.

1. Atomic size and its effect: The electron affinity of smaller atoms is higher than that of larger ones. The nucleus of a smaller atom is more alluring to the electrons than the nucleus of a larger atom. Attraction for electrons in the outer shell will diminish as atom size grows because the outer shell will be further from the nucleus. For instance, Br has a lower electron affinity than I. 
2. The electron affinity is also affected by the nuclear charge. A higher atomic charge results in a stronger electron attraction, and hence a higher electron affinity. When a molecule is already charged, the repulsion between its electrons and the pull from the nucleus both increase, leading to a lower electron affinity in the charged ion.
3. Reducing the screening effect on the inner shell of an atom increases its electron affinity.
4. The electron affinity is also affected by the electrical configuration. Inert gases will have zero electron affinity because elements with a complete octet have no propensity to receive electrons. An important factor in electron affinity is the electrical configuration. Because of their unique electrical structure, metals have a lower electron affinity compared to non-metals.

Summary

The capacity to take electrons in a gaseous state and transform into an anion is known as electron affinity. The process of receiving electrons is exothermic because it results in the release of energy. The electron affinity reduces when we travel up to down in groups and rises while moving left to right in a period. It is denoted by the symbol Ea, and it is measured in kilojoule per mole (KJ/Mol). In all cases, the electron-electron repulsion causes the first electron affinity to be lower than the second electron affinity. The electronic configuration, screening effect, and nuclear charge of elements all have a role in how strongly they attract electrons.

Frequently Asked Questions

1. Why does fluorine have less electron affinity as compared to Chlorine?

As we move along a period, electron affinity increases and decreases down a group. However, the fluorine atom is too tiny to release a significant quantity of energy. Hence, among the halogens, chlorine has the highest electron affinity value, followed by fluorine, bromine, and iodine.

2. Group 1 or group 7—which is more reactive in the periodic table?

Group 7’s nonmetals, the halogens, become progressively less reactive as you move from top to bottom of the group. This pattern runs counter to what we observe in Group 1 of the periodic table, which contains the alkali metals.

 3. What is the sign of electron affinity?

Adding an electron to an element makes it less positive, hence the electron affinity is negative at initially. Nevertheless, adding an electron to a negative ion might make it more positive or more negative depending on the nature of the repulsion between the electrons.

Introduction

The electronic configuration characterises the distribution of electrons inside a subshell of an atom. An electron configuration is a schematic depiction of the predicted location of electrons in an orbit around a nucleus. In a neutral atom, the number of electrons equals the number of protons. We can visualise the electrons’ energy and the sort of orbital in which they are located by arranging them to stand around the nucleus. Electrons inhabit certain orbitals in a specific order depending on their energy.

What is Electronic Configuration

• The electronic configuration characterises the distribution of electrons inside a subshell of an atom.
• There is a consistent format for listing the subshells of an atom that contain electrons in an atomic electronic configuration.
• When dealing with many atoms, the conventional depiction of electrical configuration might become tedious. Sometimes, a shortened or abbreviated sign can be used for the full one.
• For instance, the Cl atom has an electron configuration of \({\bf{1}}{{\bf{s}}^2}{\bf{2}}{{\bf{s}}^2}{\bf{2}}{{\bf{p}}^6}{\bf{3}}{{\bf{s}}^2}{\bf{3}}{{\bf{p}}^6}\).

Subshells

• The distribution of electrons into subshells is determined by the azimuthal quantum no., symbolised by the letter “l.”
• The magnitude of the principal quantum no., n, dictates the magnitude of this quantum number. As a result, four distinct subshells can exist when n is equal to 4.
• The s, p, d, & f subshells, accordingly, relate to l=0,1,2, 3 quantities for n = 4.
• The highest electrons no. that a subshell may hold is given by the equation 2(2l+1)
• The greatest number of electrons that the s, p, d, & f subshells can accommodate is 2, 6, 10, and 14 respectively.

Filling of Atomic Orbitals

The following concepts govern how the electrons in the atomic orbitals are occupied.

• Aufbau Principle; An atomic orbital’s energy is governed by its  principal and azimuthal quantum number. The Aufbau principle says that electrons enter relatively low-energy orbitals and go to greater energy.
• Pauli Exclusion Principle: A maximum of two electrons of opposite spins can be carried in a subshell. This makes sure that every electron has a different set of quantum numbers.
• Hund’s rule; Each orbital in a particular subshell is said to be solely filled by electrons before a 2nd electron is placed in an orbital.

Aufbau Principle

Writing the Electronic Configuration,

The above-mentioned three main rules govern the creation of electronic configuration documents. The electrical configuration of each constituent is established under their supervision. The energy of an electron’s orbit around the nucleus may be calculated for certain distances, or “energy states.” The energy associated with a certain energy state increases as one moves further from the nucleus. Yet, it is difficult for everyone to retain the electron energy level diagram for numerous electron combinations.

The subshells are filled according to the Aufbau principle. The electrons occupy this sequence:

1s,2s,2p,3s,3p,4s,3d,4p,5s,4d,5p,4f,5d,6p,7s…

A maximum of two electrons can occupy a subshell. 

Representation of Electronic Configuration of Atom

In this section, examples of a few elements’ electronic configurations are given:

• Helium:

Atomic number of Helium is 2. Its electronic configuration is \(1{s^2}\).

• Fluorine

The atomic no. of F is 9. Its electronic configuration is \({\bf{1}}{{\bf{s}}^2}{\bf{2}}{{\bf{s}}^2}{\bf{2}}{{\bf{p}}^6}\)

Summary

The electron configuration of an element represents the dispersion of electrons inside its atomic shells. As the electrons are mathematically positioned in these subshells, the configuration helps establish their location. The periodic table classifies elements into one of four groups based on the arrangements of their electrons. The s, p, d, and f blocks comprise these elements. How many electrons can fit inside a shell is proportional to the primary quantum number (n). The azimuthal quantum number (represented by the letter “l”) determines the subshell distribution of electrons.

 

Frequently Asked Questions 

1. What are isoelectronic species?

Isoelectronic species are atoms or ions with the same number of electrons in their orbital. Thus isoelectronic species will have the same electronic configuration. However, this does not guarantee the same physical and chemical properties since the atomic numbers differ. 

2. What is the importance of electronic configuration?

Electron configurations shed light on the chemical behaviour of an atom by revealing its valence electrons. It’s also useful for grouping things into categories like “s,” “p,” “d,” and “f” blocks which form the periodic table. It helps in accessing the similarity in properties of the elements. 

3. Which subshells are present for n=1?

One orbital may contain a maximum of 2 electrons. For n=1, only the s subshell can exist.  Its azimuthal number is 0. And only two electrons can be present in this subshell. Thus the possible configurations can be \(1{s^1}\) and \(1{s^2}\).

Introduction

The energy shift that occurs when an electron is added to an isolated atom is known as the electron gain enthalpy. Electron affinity is the capacity to accept an additional electron and produce an anion. Due to attaining a stable electronic structure, the elements going through this energy change or electron addition. In this process, an electron is added to chlorine to create a stable octet.

The groups 6th and 7th of the periodic table are where the majority of the electron affinities and negative ions or anions are found. In accordance with the size and nuclear charge of the elements, it can have either negative or positive values. For instance Sulphur has an electron affinity of -210 kJ/mol and chlorine has an electron affinity of -359 kJ/mol. 

Sulphur and chlorine both release significant amounts of energy, but chlorine has a greater negative electron gain enthalpy. Sulphur, however, has less negative electron gain enthalpy than chlorine. This is so because although sulphur needs two electrons to form a noble gas structure, chlorine just needs one. Chlorine rapidly accepts an electron to gain stability, but compared to sulphur, which accepts two electrons, it loses more energy and turns more negative. Only when adding an electron requires a significant amount of energy do elements also have a +ve  electron gain enthalpy. 

What is Electron Gain Enthalpy of Elements?

The process of adding an electron to create an anion is known as the enthalpy or energy change. It refers to the energy that is emitted or absorbed when an electron is introduced to a gaseous atom in isolation. The symbol for it is egH. The quantity of energy released determines how much an element’s electron gain enthalpy increases. Chlorine has a larger negative electron gain enthalpy value compared to fluorine. This is due to the fact that chlorine’s outermost shell has a lot of room for newly added electrons or incoming electrons and releases the greatest energy.

Factors that Affect Electron Gain Enthalpy

The following list of variables affects an element’s electron gain enthalpy:

• When the atomic size increases, the electron gain enthalpy falls. When the distance between the nucleus and the outermost shell widens, the huge size of an atom reduces the force of attraction for the arriving electron at the nucleus.
• The stable configuration components contain subshells that are partially and fully filled. For those elements that require to add electrons to their outermost shell in order to attain maximal stability, the electron gain enthalpy will be larger.
• Nuclear charge has a direct impact on electron gain enthalpy. The overall positive charge that the entering electron experiences makes up the atom’s effective nuclear charge. The effective nuclear charge has increased.   

Electron Gain Enthalpy in Period

The electron gain enthalpy rises in the period as we move from left to right. As we move from left to right in the period, the effective nuclear charge increases and the size of an element decreases.

Electron Gain Enthalpy Group

When an element’s size grows and its effective nuclear charge drops as we advance down the group, electron gain enthalpy reduces. The approaching electron will feel less attraction as a result. When we descend the group, electron gain enthalpy thus diminishes.

Measurement and Use of Electron Affinity

Electron affinity is a quantitative method to measure how easily an electron is added to a neutral atom, thereby forming a negatively charged ion and, hence releasing energy. It is applicable for gaseous atoms only, as solids and liquids state change their energy level due to contact with other molecules and atoms.

  

• The energy released during the chemical reaction or process is given as a negative number. Exothermic process is another name for it. Eea or EA is used to symbolise it. The unit is given in kJ/mol.
• As the amount of an element decreases in a group, electron affinities for those elements have negative values or become less negative since it takes more energy to add an electron, making \({E_{ea}}\)  less negative.
• Electron affinity is used to measure the polarity of bonds and  judge their ionic and covalent characters. 

Electron Gain enthalpy 

One-Electron Reduction

The gain of electrons or the addition of electrons to generate a negative charge on materials is known as the reduction process. It is claimed that the atom has been decreased by one electron.

Summary

The electron gain enthalpy is the amount of energy that is released when an additional electron is added to a neutral atom. In contrast, electron affinity is the tendency of an element to accept an additional electron and produce an anion. The energy released to achieve stability has a negative value when an electron or first electron is added. The electron gains enthalpy or a negative value as more energy is released. An anion’s value becomes less negative or positive as a result of the addition of a second electron because of the stronger repulsive forces that arise from having more electrons in the system.

Frequently Asked Questions

1. Comment on electron gain enthalpy of electropositive elements.

Electropositive elements have a tendency to lose electrons and form stable cations. As a result, adding one electron requires a lot of internal or external energy, hence their electron gain enthalpy will be positive.

2. Why is electron gain reaction exothermic?

When an electron is introduced to an isolated gaseous atom to create an anion, energy is released. The neutral atom attains a stable electronic configuration which results in release of energy.

3. What is the enthalpy of electron gain for group 18 elements?

The outermost shell of group 18 elements are completely occupied, and their electronic configurations are constant. When adding electrons demands a significant amount of energy, the electron gain enthalpy turns positive.

Introduction

As an electromeric action, the intramolecular electron transfer phenomenon makes molecules temporarily become polarisable. This result is frequently referred to as the conjugative mechanism or the tautomeric mechanism.

It is frequently considered with other effects like an inductive effect and a mesomeric impact. Although others also acknowledge this, it is not clearly stated that the existence of the agency in question affected this. The phrase “electromeristic effect” is not even addressed in conventional textbooks. It also affects a certain form of resonance. A curving arrow is used to symbolise the electron shift that results from this occurrence metaphorically.

What is the Electromeric Effect?

Electromeric refers to the transient occurrence that includes the full transfer of electron pairs in one of the bound atoms in a multiple bonded species. They must be related to double bonds or triple bonds if they have many bonds. And it only takes place when a reagent is present. It is a transient Polaris power that was created on several coupled species, and it vanishes as the attacking reagent is withdrawn. As a result, once the attacking chemical was removed, the molecule once more reverted to its natural form. The electromeric effect has no clear direction, although an electron pair is more frequently transferred to the element with higher electronegativity. When numerous bound species exhibit an electromeric effect, their teri activity rises, and as a result, a number of new products are produced. Only organic substances contain it. Moreover, when nucleophiles or electrophiles are present, a reversible reaction takes place. The example below demonstrates the electromeric effect.

The direction of the Shift 

The molecules, or the atoms linked to the bonds, determine the direction of the electron shift.

1. If more of the atoms connected to the double bond share the same traits, an electron pair may flow in any direction.
2. Hence, in such circumstances, the flow of electron pairs will become unpredictable.
3. When the atoms bound in the numerous bonds are distinct, the movement of electron pairs becomes equivalent to the direction of the inductive effect.
4. Under these circumstances, the dipole moment affects the electron flow.

Mechanism of the Electromeric Reaction

The electromeric effect’s mechanism is simple to comprehend. In that situation, the double or triple bond’s electron pair location transfers to one of the atoms that are connected to the double or triple bond. And it only takes place when an electrophile or a nucleophile is present. For instance, when cyanide is present in the process below, electron pairs are moving in favour of the atom of oxygen. And after the reagent is removed, this effect is undone.

Types of Electromeric Effect

Positive electromeric effect, abbreviated +E, and negative electromeric effect, abbreviated -E, are the two main forms of electromeric effect.

• The +E effect is seen in reactions where the reagent is an electrophile; because electrophiles are positively charged chemical species, the electron pairs in the numerous bonds are moved towards the reagent. This indicates that the provided molecule’s pair of electrons is being taken by the reagent. And the reagent helps to create a new connection.
• The -E effect occurs in a reaction in which nucleophiles are used as the reagent. The electron in the reagent will go towards the molecule in such reactions if the reagents are abundant in electrons. Considering that negatively charged organisms seek out a bright side. An illustration of a detrimental electromeric action is the addition of cyanide to ketones and aldehydes.

Positive Electromeric Effect

Examples of the Electromeric Effect

Here are some instances of reactions that exhibit electromeric effects.

• The electromeric effect is produced by the nucleophilic addition of certain nucleophiles to the carbonyl compounds. Nucleophiles are added to the positive side of carbonyl compounds because they are negatively charged.
• Electrophiles and nucleophiles can be found in hydrogen halides. They contain an electrophile that attacks the electron pair, removes the electron, and causes the creation of a bond. The reaction is finished when a nucleophile is present.
• Polarisation is produced by the electrophilic addition process, which involves adding an electrophile to symmetrical alkynes or alkenes.
• Benzenoids undergo electrophilic substitution reactions: The presence of electrophiles causes benzene to become polarised

Differences Between Electromeric Effect and Inductive Effect

These two impacts differ in a few ways, which are shown below in a table:

Difference Between Electromeric and Mesomeric Effects

The differences between the electromeric and mesomeric effects are given below:

Summary

A phenomenon known as the electromeric effect occurs in unsaturated chemical molecules. The development of polarisability is a transient phenomenon. They fall into one of two categories: electromeric effects, both positive and negative. These occurrences only take place when an outside reagent is present. These substances might be electrophilic or nucleophilic. Numerous instances demonstrate the electromeric effect. Examples of this phenomenon include electrophilic and nucleophilic substitution. This reaction’s mechanism is quite straightforward to comprehend. It differs greatly from other effects like the mesomeric effect and the inductive effect. Also, it has a reverse impact.

Frequently Asked Questions

1. How come  the electromeric effect is transient?

After the attacking agent is eliminated, the pi electron pair returns to its original place and forms another multiple bond. The electromeric effect is thus a transient phenomenon, and the resulting product can not be isolated

2. Does the +E effect make the substrate a nucleophile?

No, the +E effect makes the substrate an electrophile. This is because there is a decrease in the electron density on the aom undergoing +E effect as a result of electron donation. The substrate can easily be attacked by a nucleophile

3. Which effect is more stabilizing electromeric effect or hyperconjugation?

The electromeric effect is more stabilizing than the hyperconjugation effect. This is because electromeric results in conjugation, which leads to the release of a lot of excess energy. Hyperconjugation involves no pi-electron conjugation. 

Introduction

A lattice crystal has a Frenkel Defect if an ion or maybe an atom occupies a location that shouldn’t be there. Yakov Frenkel, a Russian scientist, is honoured with this name. One atom in the crystal intentionally moved its position, creating the void. Due to the presence of valencies and self-interstitial defects, this flaw is frequently referred to as a dislocation defect. Crystal lattice sites become vacant when little cations are displaced from their usual positions.

Formation of Frenkel Defect

Frenkel defect can arise in crystal due to following reasons:

1. A cation exits the lattice as well as becomes interstitial.
2. A void is produced in the lattice.
3. The uprooted cation settles in a nearby position among the other cations as well as anions.

Occurrence of the Imperfections in Solid Crystal

One of the most distinguishing features of crystals over amorphous substances is their ionic alignment. Yet, as no material exists in a perfectly ordered state, lattice flaws are always present.

Defects can be thought of as imperfections. The science of solid-state chemistry investigates the imperfections of solid crystals. A perfect crystal unit might contain anything from one atom to an infinite number of atoms. Crystal faults are the names given to certain imperfections in a crystal. Hence, imperfections in the crystal structure are known as crystallographic defects. Crystallographic flaws come in a wide variety of shapes and sizes, from points to lines to planes. Frenkel faults are localised imperfections. Several different types of flaws may be found, including:

1. Impurity Defects  
2. Stoichiometric Defect,
3. Frenkel Defect
4. Schottky Defect

Frenkel Defect Example

Some examples of Frenkel Defect are as follows:

1. Silver Bromide
2. Silver Chloride
3. Potassium chloride

Frenkel Defect Diagram 

Reasons for the Frenkel Defect

Due to the unit cell features at repeated fixed distances, defects are common in solid-state formations because the placements of molecules or atoms in crystals are predetermined. Particle irradiation is a major source of these flaws. The structure of a crystal is often imperfect and unstable. To put it another way, the equilibrium does not exceed the detection limit since the enthalpy of production is higher than at any other period during particle irradiation. Materials containing displaced cations are also susceptible to the formation of these flaws spontaneously.

Calculation of Number of Frenkel Defects

The Frenkel defect may be calculated using the following formula:

Where,

N = normally occupied positions

N‘ = no. of available positions

H = Frenkel Defect’s enthalpy formation per atom

R = gas constant

T = temperature

Difference between Schottky and Frenkel Defect

Some key differences between Schottky and Frenkel Defect are:

Summary

A Frenkel defect occurs when an ion or atom occupies a vacant site in a crystal lattice. A site vacancy is created when a cation moves, and it fills in at a neighbouring site. Particle irradiation results in this flaw. The Frenkel flaw has no effect on the chemical properties. It does nothing to increase the crystal’s density or make it non-conductive. Frenkel defect is proportional to the number of occupied and unoccupied areas, as well as the temperature. Because of the movement of ions, Frenkel defect is sometimes referred to as a dislocation defect.

Frequently Asked Questions

1. Why can the s group elements not show Frenkel defect?

The atomic defect indicated necessitates a low coordination number and molecule-friendly crystal lattices. The defect does not exist in alkali metal halides because cations and anions are almost the same size and cations cannot be accommodated in interstitial regions.

2. What is special property of AgBr crystal?

Frenkel and Schottky defects are both seen in AgBr because to its intermediate radius ratio. AgBr displays Schottky defects when both anions and cations are absent from the crystal lattice. The Ag+ ions in a material are very mobile and tend to move across the lattice. This causes them to exhibit the Frenkel flaw as well.

3. Does Frenkel Defect affect physical properties of a crystal?

The defect has an immediate effect on ion migration, but it has no effect on the solid-state structure’s volume or density. Thus, it does not affect the physical properties of crystal. As atoms pack closely together, stresses develop between them, leading to lattice growth. This growth more than compensates for the contraction of the lattice caused by vacancy.

Introduction

Poly halogens can be broken down into subgroups. Due to their widespread use, important poly halogens include Freons, DDT, and carbon tetrachloride. Carbon tetrachloride is a colourless, combustible liquid with no discernible odour. Commercial and household use of carbon tet as a cleaning agent was popular before 1970.

Users are put in danger when these refrigerants escape into the air. This calls for the development of innovative, safe, and non-toxic refrigerants. DDT (dichloro-diphenyl-trichloroethane) was developed in the 1940s and was the first of the modern synthetic pesticides. It was first employed to treat military and civilian populations for insect-borne ailments, including malaria and typhus.

Polyhalogen Compounds

Polyhalogen compounds are those that include several halogen atoms (elements in group 17 of the modern periodic table). In both manufacturing and farming, poly-halogen compounds are a common staple. They have several applications and are widely employed as pesticides, solvents, and anaesthetics.

There are several important poly-halogen compounds, but some of the most well-known are methylene chloride, chloroform, carbon tetrachloride, iodoform, DDT, and benzene hexachloride.

Freons

Freons, or chlorofluorocarbons, are a popular refrigerant. Fluorine and chlorine atoms are substituted for the hydrogen atoms in methane  (\(C{H_4}\)) to produce it. The properties of CFCs may be altered by including different numbers of chlorine and fluorine atoms. The rule of 90 is used as a naming convention for chlorofluorocarbons. The CFC is commonly referred to as CFC-n, where n is any of the numbers listed below. Following that pattern, we may deduce n by subtracting 90 from the total number of fluorine, hydrogen, and carbon atoms given. If, for example, a CFC’s formula is \(CC{l_3}F\), then that CFC is designated as CFC-11.

Freon Structure

Structure

Molten sodium and heated, concentrated mineral acids have no effect on Freons. Therefore, as the ratio of fluorine to carbon atoms in Freon gas increases, the length of the resulting solid C-F bonds decreases. C-F bond lengths range from 1.29 to 1.358 angstroms for molecules like  \(C{H_3}F\), \(C{F_2}\) etc.

Synthesis

Antimony fluoride reacts with carbon tetrachloride to produce freon and Antimony Chloride, which acts as an autocatalyst. 

To create chlorofluorocarbons, chlorinated methanes and ethanes are commonly subjected to a halogen exchange reaction. The process of converting chloroform into chlorodifluoromethane is outlined below..

Uses

Due to their low boiling points and low viscosity, freons are widely used as refrigerants in:

• Mechanical cooling and refrigeration devices
• Aerosol propellers
• Ingredients for Foam Blowing
• Solvents
• Glass and intermediate polymer coolers
• Inhalants are widely used legal medications that are ingested through the respiratory system. Inhaling gasoline, paint thinners, sprays, or refrigerant gases is a common way to get high.

DDT

The chemical formula for DDT, or dichlorodiphenyltrichloroethane, is \({C_{14}}{H_9}C{l_5}\). This chemical compound is a crystalline solid that is odourless, tasteless, and colourless under typical pressure and temperature conditions.

In 1939, Swiss chemist Paul Hermann Müller developed DDT’s insecticidal properties. In the latter years of World War II, DDT protected civilians and military personnel from insect-borne diseases, including malaria and typhus.

Structure

DDT is composed of 2 phenyl groups with five carbons as substitutions. The chemical formula of DDT is \({C_{14}}{H_9}C{l_5}\). DDT and its IUPAC name is 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane. 

Synthesis

To produce DDT, a mixture of chloral and chlorobenzene (in a ratio of 1:2) is cooked in strong sulfuric acid.

Uses

In addition to solutions in xylene or petroleum distillate, DDT is also available as emulsifiable concentrates, water-wettable powders, granules, aerosols, smoke candles, vaporisers, and lotion charges. Agriculture made heavy use of DDT between the years 1950 and 1980. Fifteen different firms around the United States worked together to produce it. DDT was also used inside structures as a pesticide. Malaria, typhus, body lice, and the bubonic plague were some diseases it was used to combat.

Carbon Tetrachloride

The chemical tetra chlorocarbon was created in a lab; it does not occur naturally. It’s a transparent liquid with a barely discernible sugary scent. Benziform, perchloromethane, methane tetrachloride, carbon chloride, and methane tetrachloride are some of its alternate names. Carbon tetrachloride is a colourless gas that regularly floats in the air.

Structure

The Lewis structure of carbon tetrachloride consists of a single carbon atom in the middle, surrounded by four chlorine atoms. Molecular \(CC{l_4}\). and its electron geometry are both tetrahedral in form. A bond angle of 109.5 degrees is found in \(CC{l_4}\).

Synthesis

French chemist Henri Victor Regnault figured a combination of chloroform and chlorine to produce carbon tetrachloride:

Uses

The various uses of Carbon tetrachloride are:

• Tetrachlorocarbon is used as a solvent in pesticides.
• Fire extinguisher and degreaser
• Remover of Spots
• Making propellants for aerosol cans and cooling fluid.
• As a result of the harm they cause, only a small number of industrial uses are allowed.

Summary

Carbon compounds with more than one halogen atom are referred to as poly halogens. Polyhalogen compounds include freons, DDT, and carbon tetrachloride, amongst others. These poly halogens can be utilised in a variety of contexts. While Freons are used to produce refrigerants and aerosols, DDT and carbon tetrachloride are utilized in the agriculture sector as effective insecticides.

Frequently Asked Questions

1. What effects are associated with the exposure of Freons to UV light?

In the event that Freon does in fact include atoms of chlorine, the chlorine that is extracted from Freon by UV light forms a chemical connection with ozone.

Because of this, ozone cannot quickly revert back to its natural state, which leads to the destruction of ozone and the formation of ozone holes in space.

2. How is DDT toxic?

DDT is toxic because it causes severe diseases in human and animal bodies when ingested. It can cause growth defects, and reproductive issues, it is carcinogenic and it can also cause nervous diseases. 

3.What environmental act talks about carbon tetrachloride?

Carbon tetrachloride was a chemical that was used for dry cleaning and as a fire extinguisher before it was made illegal worldwide in 1987 under the Montreal Protocol. It damages the ozone layer and contributes to the ozone hole that has formed over Antarctica.

Introduction

One type of electrochemical cell is the electrolytic cell (EC), which converts electrical energy into chemical energy. This process causes an artificial redox reaction. Electrolytic cells may break down a wide variety of chemicals. It’s a technique for getting rid of ions in a mixture. The reduction half-cell and the oxidation half-cell together make up a single electrolytic cell. Energy for voltaic cells (VC) comes from a chemical reaction that happens naturally and results in a flow of electrons across a circuit (external). These cells are essential because they form the backbone of batteries, which provide the energy that runs modern civilization. Electricity is typically used to fuel non-spontaneous processes.

About Electrolytic Cell

It’s a device for electrolyzing a chemical compound, or breaking it down using an electric current. Simply put, this is a specific kind of electrochemical cell. Hydrogen (\({H_2}\)) and oxygen (\({O_2}\)) are produced when water is electrolyzed. Here, a bit of more power is required to get beyond the threshold energy level.

The electrolyte in these cells is often a fused or disintegrating ionic compound, and the cell itself consists of two electronic or metallic conductors (electrodes) that are either separated from one another or remain in touch with one another.

One of these is the use of a direct electric current source to link these electrodes, which keeps one of them negatively (-vely) charged while leaving the other, maybe positively (+vely), charged.

The cathode (-ve) moves the anode (+ve) and transfers one or more electrons to the cathode. This creates brand-new particles, either neutral or ions. Electron transmission is the determining factor in the cumulative effect of these two processes.

Galvanic Cell and Electrolytic Cell Comparison

Both electrolytic and galvanic cells function in the same way. There are three main features that make electrolytic cells and galvanic cells similar: Both cells need a salt bridge for proper functioning. Electrons (e-) always flow from the anode to the cathode, and both have cathode and anode components.

Difference Between Galvanic Cell and Electrolytic Cell

Electrolytic Cell Application

Some of the applications of electrolytic cell are

1. Generation of oxygen gas from water .
2. Electroplating
3. Electrorefining.
4. Electrowinning 
5. Isolation of metals of commercial importance such as aluminium, gold, copper, zinc, etc. 

Properties of Galvanic and Electrolytic Cells

Galvanic cells (GCs) are devices used to convert chemical energy into electrical energy. Electrolytic cells are capable of converting electrical energy into chemical energy. A salt bridge unites two segments housed in separate containers. The oxidation reaction takes place at the anode, and the redox reaction at the cathode. Electrons (e-) are supplied by an external cell and flow from the cathode to the anode.

Working Principle of an Electrolytic Cell

Electrolytic cells are instruments based on the idea that during an oxidation-reduction reaction, electrons (e-) are transferred from one chemical species to another.

Lets take the example of electrolysis of NaCl. 

Sodium metal and chlorine gas are produced during the decomposition of molten sodium chloride (NaCl).

Electrolysis occurs when a second energy source is applied to a vessel containing molten sodium chloride and carbon (C) electrodes. At the cathode end, the Na+ ion will be neutralised by the flow of electrons (e-) from the anode.

Although the anode and cathode retain their traditional roles, oxidation and reduction now occur at the cathode and anode, respectively. The electrolyte cell’s operational parameters are crucial to its proper functioning. Even the most potent reductant will succumb to oxidation. The most oxidising substance will be the one to be depleted.

The success of the Electrolytic Cell Molten sodium chloride (NaCl) depends on the electrolysis process, which is an integral part of the electrolytic cell.

Electrolysis of NaCl

Two non-active electrodes are submerged in a bath of liquid NaCl. Dissociated Na+ cations and Cl- anions are present here. The cathode is the part of the circuit where electrons (e-) gather when an electric current is sent through it. As a result, the resulting charge is negative (-ve). Because of this, the positively charged sodium (Na) cations go to the cathode, which is negatively charged. This results in the formation of sodium metal (Na) at the cathode.

Chlorine Cl atoms are transferred to the cathode during this process. It causes chlorine gas to be generated at the anode (Cl2). Two electrons (e-) are then freed, completing the circuit. In an electrolytic cell, molten NaCl is electrolyzed to produce Na and Cl2 gas, two metals (EC).

Summary

An electrolytic cell (EC) is a device that converts electrical energy into chemical energy via a non-spontaneous redox action. A reduction half-cell and an oxidation half-cell make them up. An electrolytic cell consists of the cathode, anode, and electrolyte. Similarities and differences exist between electrolytic cells and galvanic cells. As an example, the electron (e-) in each cell is unique. Understanding electrolysis requires familiarity with Faraday’s laws. The magnitudes of electrolytic effects are defined by them.

 

Frequently Asked Question

1. Define EMF?

Maximum potential difference between a cell’s electrodes is its electromotive force (EMF). The net voltage between the oxidation and reduction halves of a process is another way to think about it. The electromotive force (EMF) of a cell is the primary criterion for establishing the galvanic nature of an electrochemical cell.

2. What is the meaning of zero EMF in a battery?

After the chemical process within a battery is complete, the anode and cathode have the same number of electrons, and the electrical field between them is zero. When a reverse field is applied to a rechargeable battery’s contacts, the battery’s chemical makeup is returned to its previous state, allowing it to once again discharge electrons in an electrical circuit.

3. What is the relation between the current and the electrolytic product? 

The 1st law of Faraday says that the amount of electric current flowing through an electrolyte causes the same amount of chemicals to build up as the amount of current. Faraday’s law of electrolysis says that when the same amount of electric current flows through many electrolytes, the amount of materials that build up is proportional to their chemical equivalent.

Introduction

Acceleration is a physical quantity that describes change in velocity over a given time interval. It is a vector quantity with both magnitude and direction, and is measured in metres per second squared (\(m/{s^2}\)). Acceleration can be thought of as the derivative of velocity or the second derivative of position.

An object moving at a constant velocity has zero acceleration. Thus, acceleration occurs when an object changes its speed or direction, and it is a measure of an object’s ability to reach a given speed.

There are two types of acceleration: average and instantaneous. Graphs, such as velocity-time, position-time, and acceleration-time graphs, can be used to mathematically represent the motion of an object and develop a better understanding of its motion.

What is the Acceleration-Time Graph?

The acceleration-time graph is a pictorial representation of an object’s motion wherein, time is taken on the X-axis as the primary variable, and acceleration is represented on the Y-axis as a function of time.

The area of this graph gives velocity, whereas its slope leads us to a physical quantity that is known as jerk.

Acceleration-Time Graph Explanation

Since the acceleration in such graphs is shown as a function of time, they can be used to understand how an object’s acceleration varies over time. If the graph is going down with time, it means the object is losing acceleration.

When an object undergoes negative or reverse acceleration, it is said to experience retardation.

Special cases in acceleration-time graph

• When particle moving with constant acceleration: If the acceleration of a particle is a constant given by at time , which does not change with time, it will be represented by a horizontal line in the graph.

Uniform acceleration

• When a particle is moving with increasing acceleration at constant rate: Acceleration that is increasing at a constant rate will be shown by a straight line making an acute angle with the x-axis or the horizontal.

Increasing acceleration

• When a particle is moving with decreasing acceleration at constant rate: If the acceleration is decreasing at a constant rate, it is bound to reach zero after a given time interval. Thus, such a graph is a straight line making an obtuse angle with the x-axis.

Decreasing acceleration

Vertical Axis

The acceleration of an object is displayed on the Y-axis of a graph, with time on the X-axis. This allows us to see how acceleration changes with respect to time.

Acceleration-time graph

Slope of the Acceleration Graph

Given a graph, we can calculate its slope, which would allow us to measure its steepness. For an acceleration-time graph, the slope represents the change in acceleration over time, which is known as jerk. In mathematical terms, it is the third derivative of the position vector. The sensation of jerk is experienced when there is a change in acceleration with respect to time.

\(\begin{array}{l}Slope = \frac{{\Delta y}}{{\Delta x}}\\jerk = \frac{{Change\;in\;acceleration}}{{change\;in\;time}}\end{array}\)

Acceleration-time graph

Jerk: Jerk is the rate of change of acceleration. The derived unit of jerk is

Thus, its unit is \(m/{s^3}\).

The dimension of jerk:

Example of jerk: Suppose a car is in motion with a given acceleration and the driver suddenly notices a speed bump. He will slow down rapidly and thus, the car’s acceleration changes abruptly in a short period of time. This sudden change in acceleration creates a jerky motion for objects inside the car, which is an example of jerk in action.

Area Under the Acceleration Graph

When we calculate the area under an acceleration-time graph, we arrive at the object’s velocity. This is easy to prove since area of a curve is given by xy.

Velocity: Velocity represents the time rate of change of an object’s displacement.

\(Velocity = \frac{{displacement}}{{time}}\)

Its SI unit is  and dimension is \(\left[ {L{T^{ – 1}}} \right]\).

Important Things To Remember In Acceleration Time Graph

• The slope of an acceleration-time graph gives us jerk.
• Two objects have coinciding acceleration-time curves when their accelerations are the same.
• Motion with constant acceleration would yield a straight line curve with zero slope, i.e., the line would be horizontal.

Acceleration Graph Solved Example

Example 1: Using the given graph, find velocity.

Acceleration-time graph

Solution: We can see that in the curve,

\(\begin{array}{l}a = m/{s^2}\\t = 4s\end{array}\)

Area under the curve will give us the velocity of the object.

\(\begin{array}{l}Velocity = acceleration \times time\\v = 15m/{s^2} \times 4s\\v = 60m/s\end{array}\)

Hence the velocity of the object is .

Example 2: If the acceleration of a car is given as , find the jerk at time .

Solution: We are given that

Since jerk is the first order derivative of acceleration. Thus,

Therefore, the jerk experienced the car is 40 \(m/{s^3}\) in the x-direction.

Summary

In a graph showing the variation of acceleration with time, time is represented on the x-axis and acceleration on the y-axis. This is because time is a primary and independent quantity whereas acceleration depends on time.

The slope of the acceleration-time graph represents the rate of change of acceleration, commonly known as jerk. Jerk is felt by the body when there is a sudden change in acceleration with respect to time and can be calculated as the third order derivative of the position vector. Just like acceleration, jerk is a vector quantity with both magnitude and direction.

Frequently Asked Questions

1.How can we find the jerk from the acceleration-time graph?

Jerk is the slope of the acceleration-time graph and can be calculated thus.

2. How can we find velocity from the acceleration-time graph?

If we wish to find velocity, all we need to do is calculate the area under the curve.

3. What is the use of an acceleration-time graph?

The graph helps us pictorially represent an object’s motion and calculate associated quantities of motion.

4. What is the relation between jerk and position vector?

Jerk is the third order derivative of the position vector.

Introduction

An immune system is a very essential system of the human body that helps protect one’s self against various harmful materials. The immune system not only fights the antigen upon invasion but also identifies the invader and retains its memory. An allergy is when a person’s immune system reacts adversely to harmless substances such as dust, pollen, any specific edible item, etc. Autoimmune disease on the other hand is a condition wherein a person’s immune system unintentionally targets his/her own cells and tissues.

Allergy

Allergy is the body’s response to common, completely harmless environmental elements that pose no threat to the majority of people. Allergens are the chemicals that cause allergies. People constantly come into contact with the environment, which exposes them to allergens such pollen, dust mites, animal fur, mildew, and insect venom.

While many people lead normal lives, some people experience negative side effects after being exposed to certain substances.

Allergic responses can be-

• A minor allergic reaction- It may only affect one area of the body that has been exposed to an allergen.
• A moderate allergic reaction-If the allergen spreads and affects nearby body parts then it is a moderate allergic reaction.
• A severe allergic reaction- If a sudden, life-threatening ailment develops, then it is a severe allergic reaction.

Symptoms of allergy

Based on the allergen and the site of exposure, an allergy can result in a variety of reactions, some of which are described below as frequent ones.

• Red and inflamed eyes, itching
• Sniffling and a runny nose
• Hives or skin rashes
• Swelling of the lips and mouth
• Itchiness in the mouth,
• Persistent cough
• Inability to breathe
• Chest constriction,
• Vomiting and nauseous
• Diarrhea
• Headaches

Symptoms of allergies

Autoimmunity 

Autoimmunity is the immune system’s reaction against oneself and healthy cells, which causes organ failure or damage along with significant physiological changes. The immune system of the human body triggers an immunological reaction to any foreign substances (antigens) that may be capable of causing disease. White blood cells  fight the antigen directly or indirectly create antibodies against it and protect the body.

In autoimmunity the  individuals make autoantibodies which attract the  autoantigens or healthy tissues and organs of the individual’s body and lead to various kinds of autoimmune diseases. Although the specific causes of some autoimmune diseases are unknown, genetic and environmental factors are being researched as potential contributors.

Types of autoimmune diseases

Based on the areas where the autoimmune attack occurs, two types of autoimmune diseases exist they are-

Organ-specific autoimmune disorders:

• As the name implies, the immune system only targets a particular organ or tissue and autoantibodies are focused on that particular organ.
• Examples include Grave’s disease and Hashimoto’s disease, both of which affect the thyroid gland and cause it to malfunction.
• White patches of skin are a symptom of the autoimmune disease vitiligo, which affects just the skin since the melanocytes that produce colour are the target cells for the autoantibodies.
• Addison’s disease develops when the adrenal cortex is attacked by self immune system.

Systemic autoimmune disorders:

• The impacts of systemic autoimmune diseases are extensive, causing many tissue damages  in numerous organs.
• Examples include Systemic lupus erythematosus, which causes inflammation, tissue damage, and tiredness in the joints, kidneys, brain, lungs, skin, and blood vessels
• The damage to the articular cartilage that lines the elbows, shoulders, knees, and hips is known as rheumatoid arthritis and is one of example of autoimmune disease

Symptoms of autoimmune diseases

The symptoms of autoimmune disease vary depending on the organ affected.It  affects the organ’s physiology and functionality both. The following is a list of the common signs of autoimmunity.

• Fatigue
• Muscle aches
• Aching and swollen joints
• Recurrent mild fever
• Skin irritation
• Legs and hands are numb

Difference between Allergies and Autoimmunity 

Summary 

Humans are endowed with a powerful immune system that can recognise and eliminate potentially dangerous chemicals from the body. The battle goes beyond mere eradication; it also records the antigen in the body’s memory, making it capable of withstanding future attacks. The immune system’s effectiveness can be compromised by autoimmune and allergic illnesses. Immune reactions are triggered in allergic people by ordinary items that are typically harmless. When the body targets its own tissues and organs thinking they are foreign objects it leads to autoimmune diseases .

Frequently Asked Questions

1. What is Anaphylaxis?

Ans: An unexpected emergency known as anaphylaxis can cause due to an allergen and lead to severe throat swelling, eye irritation, breathing and swallowing difficulties etc.

Due to a quick reduction in blood pressure, some persons under an  anaphylactic attack feel dizzy.

2. How are allergies identified?

Ans: A skin test and blood test are used to diagnose allergies. An allergen drop is applied to the skin and pricked softly to perform a skin prick test. A blood test counts all IgE antibodies produced in response to a specific antigen.

3. What effect do immunosuppressants have on autoimmune disease patients?

Ans: An immune reaction against self-tissues is elicited by an overreacting immune system in an autoimmune disease patient. Immunosuppressants lower the body’s immunological response, but they can have negative side effects include a higher risk of infection.

Introduction: Evolution

It was once thought that all life forms on earth were created exactly as they are now. Some people believed that the earth’s living things originated on another planet and were then brought here. Many outdated preconceptions were swept aside by the idea and theory of evolution. According to the concept of evolution, all complex species descended from a single, primordial ancestor, from which they evolved by a series of small, progressive changes in response to the environment.

This shift is a gradual process that has occurred, is occurring, and will continue to occur. This is due to the fact that living things adapt to their ever-changing circumstances and develop characteristics that are essential to their survival.

Such a slow and gradual process that resulted in the occurrence of new traits within a population and gave rise to new species is called evolution. Evolution is fueled by a variety of processes, including gene mutations, genetic drift, gene flow, non-random mating, and natural selection. After hundreds of years of evolution, new life forms that outnumber some species are created that are better suited for survival. 

Is Evolution a Random Process?

The creatures experience genetic alterations, which show up in their physical characteristics. Individuals with acquired genetic qualities outlive their contemporaries more successfully than those without them. Over time, acquired physical traits are passed on to the following generations. In order to survive, an individual must obtain food and stay away from predators.  Although evolution is a gradual process, the factors like genetic drift and mutation that contribute to mutation are random.

Factors Contributing to Evolution

Mutation

Changes at the DNA level, such as mutations and recombinations, produce new alleles, which are then thought of as the cause of novel phenotypic traits. These alleles are spread throughout a population through breeding and are only passable through sexual chromosomal alterations. These hereditary traits and acquired traits develop through breeding generations to become distinctive characteristics of that particular group. The population finally diverges in various ways from its ancestor. Those lacking inherent adaptive characteristics fade away when faced with unfavorable conditions. While those with adaptable traits pass them on to their offspring and grow in number. Evolution is influenced by mutations in this way. Some mutations are detrimental and dangerous because they interfere with an organism’s ability to survive. During development, this can result in lethal circumstances. Additionally, since genetic mutations are unpredictable, they cannot be the only force behind the extensive process of evolution.

Mutation and selection

Genetic Drift

There may occasionally be abrupt and arbitrary shifts in allele frequencies within a small population. Regardless of the benefits or drawbacks of a given allele, it may even result in its eradication. Genetic drift is the term for the haphazard evolution that occurs in small populations as a result of variations in allele frequency. Despite the fact that it can happen in huge populations, its effects on evolution are best seen in small groups. For instance, a population that recently experienced a natural disaster that significantly reduced its size experiences genetic drift. It might result in the eradication of a certain allele from the population. Genetic drift, however, occurs by chance.

Natural selection

Natural selection is a purely selective process in which those with superior features earn the capacity to survive. The survival of any population and its propagation greatly depends on its interaction with the environment, regardless of how much a mutation or genetic drift contributes to a physical change. Every individual in a population goes through a serious struggle just to survive. New characteristics that are necessary for an individual’s survival are preserved by natural selection. It facilitates the selection of advantageous features required for better environmental adaptability of organisms. Individuals who possess positive attributes tend to reproduce more frequently. In this approach, unfavorable features gradually become less prevalent across the board due to natural selection. Due to this, evolution appears to be a more deliberate process than a sudden and haphazard one.

Are evolution and “survival of the fittest” the same thing?

Natural selection operates through a mechanism known as “survival of the fittest.” In his postulates, Charles Darwin claimed that people compete with one another in order to survive. He described it as a struggle for survival.  Individuals within a species or between species may compete for food, territory, water, light, and mates (in cases of sexual reproduction).  Only those who are capable enough can withstand this competition and live. Darwin claimed that only those who are “fit” enough can “survive,” in other words.

The survival of the fittest is not the same as evolution, which is a more general concept. According to the theory of survival of the fittest, those with desirable traits can pass those traits down to future generations while eradicating the population’s bad features. In order to speciate (create new species), evolution demands that the strongest individuals overwhelm the weaker ones.

Summary 

The evolution of all living species on earth has been gradual and slow. Several factors, including gene mutations, genetic drift, and natural selection, support it. Physical characteristics are acquired as a result of genetic diversity. Darwin claimed that there is fierce competition between members of the same species or distinct species for resources including food, water, space, light, and mate. Those who are physically capable can survive. Fitness has less to do with physical fitness and more to do with an organism’s capacity to prosper in its environment. A species doesn’t just appear; it takes millions of year.

 

Frequently Asked Questions  

1. What is the meaning of macroevolution and microevolution? 

Ans: Evolution is a change in an organism’s genetic makeup that leads to some degree of speciation. The naked eye cannot see changes in DNA sequences or allele frequencies. It’s known as microevolution. Larger changes in physical features and consequently performance, combined with other factors like natural selection, result from changes in genetic makeup, leading to the emergence of new species. It’s known as macroevolution.

2. Is there any relation existing between the species surviving in this world?

Ans: Earth’s species share a common ancestor. By passing features down from one generation to the next and repeatedly splitting from the original species, species evolved from a common ancestor over millions of years. This develops over many generations and creates new species that are completely distinct from their ancestor.

3. How can understanding anatomy help in understanding evolution?  

Ans: In order to understand the lineages, scientists examine the physical characteristics of living species and contrast them with those of extinct species. Tracing the changes in an anatomical feature over the years helps to understand the probable changes that must have occurred in the environment through the years that forced the changes that have occurred.