Introduction

The electron (e-) is a particle of an atom, just as an atom is a substructure of matter. There is no way to create or destroy these atoms. Atoms were assumed to be the smallest unit of a particle before the discovery of electrons (e-). Tests used in the discovery of the electron shed light on some of the atomic basic features (e-). It was a major turning point in physics when the electron (e-) was discovered as the first subatomic particle. It turns out to be one of the most crucial in modern chemistry and physics for defining the chemical bond.

Thomson Cathode Ray Experiment

J.J. Thomson (J.J.T.), a physicist, studied CRTs (cathode ray tubes) in the early 1990s (CRT). A glass tube, sealed under vacuum, is present. Particles are accelerated from the cathode to the anode as a high voltage is supplied between two electrodes on one side of the tube.

Cathode-ray tubes get its name from the fact that the cathode is the point of genesis for the particle beam (CRT). Phosphors produce a spark or light when hit by the beam. Thomson investigated the particles’ properties by surrounding the beam with two electric plates that were charged in the opposite direction. A positive electric plate was used to deflect the beam away from a negatively charged one. This means that the particles in the beam were all electronegative.

He also found that the magnetic field could be used to redirect the beam by placing magnets on each side of the tube. After calculating the mass-to-charge ratio of beam particles, he conducted an experiment showing that the mass of a single particle was far less than that of any known atom. Cathode Ray (CR) attributes were the same and irrespective of cathode composition, he found after conducting more tests using metallic elements as electrode components. The following conclusions were then made:

1. Components of the cathode ray are all of the negative variety.
2. Particles must have been part of the atom, as their combined mass is 1 x 2000 that of a single hydrogen atom.
3. Every atomic nuclei have the potential to contain these subatomic particles.

His findings were originally controversial, but experts gradually accepted them. This cathode ray (CR) particles were subsequently referred to as electrons (e–). 

Cathode Ray Experiment

Define Electrons

The electron (e-) is a negatively charged subatomic particle with a small mass. Consequently, it may be readily deflected by approaching another e- or the positive nucleus of an atom. The discovery of this primary building block came first. These are fundamental particles with a negative one-charge. An e- has the same negative charge as a proton (but has an opposite sign).

While protons and e– have the same charge magnitudes, the former is substantially smaller and lighter than the latter. An e- is a particle with a negative charge. The negative charge is  \(1.602 \times {10^{ – 19}}\)  Coulomb in magnitude. The mass of an e- is just 1/1837 that of a proton.

Electron density: The mass of one electron is \(9.10938356 \times {10^{ – 31}}kg\)kilograms (e-).  As compared to the mass of a proton, the mass of an electron (e–) is extremely small.

Properties of Electrons

Following are the properties of electrons:

1. The positively charged protons and neutrons make up the nucleus of an atom, while the negatively charged electrons orbit around it.
2. Electrons are the sole fundamental component of an atom that cannot be further split into smaller subatomic particles like protons and neutrons. The letters e or e- stand for them in the alphabet.
3. It is possible to raise the energy level of an electron by absorbing some of its lower energy level.
4. Due to their extremely low mass of 9.10941031 kg, electrons do not contribute to an atom’s total mass.
5. A proton has a positive electric charge of +1, whereas an e- has a negative charge of -1.
6. The attraction between the negative charge of the electron and the positive charge of the protons causes the electron to go in a certain orbit around the nucleus.

Electrons and Compounds

The electron was discovered in 1897. The discovery of the proton between 1911 and 1919 and the neutron in 1932, however, recast the electron’s meaning and significance. The whole concept of atomic structure was established with the discovery of the other two subatomic particles.

The nucleus of an atom is composed of positively charged subatomic particles called protons. The number of protons in an atom and the size of an electron are both element-specific. For comparison, oxygen (O) has 8 protons and carbon (C) has 6, but hydrogen (H) has just 1.

Rutherford postulated neutrons before discovering the proton; Chadwick confirmed their existence in 1932. As neutrons have no net electric charge, they were appropriately named. All elements in the periodic table are made up of neutrons except hydrogen (H). A neutron’s mass is somewhat more than that of a proton.

Summary

Electrons were first identified as particles in cathode rays, discovered by J.J. Thomson, whose discoveries were widely accepted. As a result of his research, a revised model of the atom’s structure was created. The electron’s charge was first determined by American scientist Robert Millikan. Using electrically charged oil droplets, he determined the charge on a single electron. He determined that the charge of a single e- is  \(1.602 \times {10^{ – 19}}\)  Coulomb. Millikan determined the electron’s mass by calculating its charge and utilising J.J. Thomson’s mass-to-charge ratio. The mass of an electron is  \(9.1094 \times {10^{ – 31}}kg\)  kg. In 1906, his discovery of the electron earned him the Nobel Prize in Physics.

Frequently Asked Questions

1. Why do electrons have a “negative” charge?

As electrons repel an electric field, the negative connotation is derived from this fact. By convention, a negative charge is assigned when an electron moves from the negative to the positive pole of an electric field.

2. How are electrons able to travel about?

When an electric voltage is applied, an electric field is created within the metal. This electric field causes the flow of electrons, which causes the electrons to migrate from one end of the conductor to the other end. The electrons will migrate towards the positive side of the charged object.

3. Do cathode rays have the ability to go through glass?

Cathode rays are not visible to the human eye, but when they strike the glass wall of an early hoover tube, they excite the atoms there, which in turn causes the atoms to fluoresce, another name for the emission of light.

Introduction

John Dalton, an English philosopher and scientist, established the atomic notion in 1808 as part of his investigation of the molecular structure of matter. It asserted that everything is made up of atoms, which are supposedly tiny autonomous creatures. According to Dalton’s atomic theory, the constituent parts of these substances are atoms that cannot be broken down into smaller parts. These other elements’ atoms range in size and mass, whereas those of a particular element are nearly uniform.

John Dalton

Dalton’s Atomic Model

Indeed, matter studies have been among the most fruitful areas for scientists. Both scientists and philosophers have spent years trying to make the world easier to grasp. The properties, structure, and other characteristics of matter’s fundamental particles have long piqued the interest of scientists. Hence, several atomic theories have emerged. The idea that matter comprises smaller units, or “particles,” is credited to Democritus. Such tiny things have been given the Greek word for “indivisible” and “atom” as their name. Democritus’ Atomic Theory rests on this principle. As a result, technological infrastructure needed to be improved, and scholars knew very little about this concept then. John Dalton, a scholar from around 2,000 years ago, displayed their attempts to simplify the situation. John Dalton published his now-famous atomic theory in 1808. This hypothesis was first given by John in a paper he named “A New Chemical Philosophy,” and at the time, it was novel. Dalton’s theory revolved around two laws:

1. Law of Conservation of Mass: Antoine Laurent Lavoisier developed the principle of mass conservation in 1789. Although the creation and destruction of matter are prohibited by law, matter can transform into another form within a closed system. Scientists use this rule to preserve linear equations.
2. Law of Constant Composition:  The rule of constant composition states that a pure material always has the same number of elements. For example, the sodium and chlorine content of NaCl, the chemical formula for table salt, remains constant regardless of how much salt we manufacture.

Postulates of Dalton’s Atomic Theory

Following are the postulates of Dalton’s Atomic Theory

• All matter is composed of tiny atoms and interconnected particles.
• There is no difference in mass, size, or any other physical property between iotas of different substances. Yet, due to their different characteristics, the mass and size of particles composed of different elements can vary widely.
• It was impossible to create or destroy an atom. Yet, iotas can’t be broken up into smaller pieces.
• Atoms of various elements mix in fixed, whole-number proportions to produce compounds.
• In compound reactions, atoms might undergo transformations, form bonds, and break free.

Merits of Dalton’s Atomic theory

Some of the key advantages of the theory are:

• It provides a basic idea for telling the difference between elements and compounds.
• Several proportional rules, mass conservation, and stable proportions are all upheld.

Limitations of Dalton’s Atomic Theory

Some of the key advantages of the theory are:

• Such an atom has been repeatedly proven to be divisible. Neutrons, protons, and electrons are the three possible constituents of an atom. Remember, though, that the smallest thing that may participate in a chemical reaction is one atom.
• According to Dalton’s atomic theory, all atoms of a given element have the same mass, size, and chemical and physical properties. The density and mass of atoms are both visible differences across elements. Isotopes are different varieties of an element that have different masses. The mass numbers of the two stable isotopes of Cl are 35 and 37, respectively.
• In addition, atoms of different elements have different sizes, masses, and other chemical and physical properties. That’s not always the case, though. For example, the atomic mass of an Ar or Ca atom is 40 amu. Atoms with the same mass number form an isobar.
• According to Dalton’s atomic theory, chemical compounds are generated when different constituents mix in simple whole-number proportions. Yet, this might not be the case with more complicated chemical compounds.
• In Dalton’s atomic theory, allotropes are not accounted for. The Dalton atomic hypothesis can no longer explain the observed differences in properties among charcoal, graphite, and diamond.
• According to Dalton’s atomic theory, the atom is the smallest unit capable of participating in a chemical reaction. Several of the underlying assumptions of this theory remain valid in modern chemistry. The proposed model of atomic structure represents a significant advance in chemical theory. It’s what modern atomic theories and quantum mechanics are built on.

Influences on Modern Atomic Theory

Many advances in modern atomic theory may be traced back to Dalton’s atomic theory. Dalton’s method was not only innovative for its day, but it also served as a foundation for subsequent chemists. Ernest Rutherford, Chadwick, Niels Bohr, JJ Thompson, and others after Dalton all made important contributions to the development of atomic theory. Eventually, JJ Thompson identified electrons, and Rutherford honed the hypothesis to pinpoint the nucleus. The atomic model as we know it today is thus a product of both Niels Bohr’s model and the Quantum mechanical model. Although the field of atomic theory has progressed much over the past two centuries, much of Dalton’s original framework remains.

Summary

Our analysis leads us to the conclusion that this concept represents John Dalton’s atomic model from 1808. According to Dalton, atoms are the fundamental building blocks of all matter. It also suggests that the different masses of atoms belonging to different elements are unaffected by chemical reactions. They wondered what the fundamental particles were like, how they were put together, and what properties they had. This led to the growth of several atomic theories. It would appear that the smallest unit of a substance that may take part in a chemical reaction is the atom. Even within the same element, atoms may have different masses. Dalton’s postulates for the atomic theory do not include this. This is a flaw in some theoretical frameworks.

Frequently Asked Questions

1. How does the presence of subatomic particles lead to the failure of Dalton’s atomic theory?

Thomson’s discoveries on subatomic particles were groundbreaking. This proved Dalton wrong when he claimed such atoms are the smallest possible material component. Thomson concluded from his findings that electrons are fundamental building blocks of atoms.

2. Which is the latest atomic model?

The electron cloud model is one of the most sophisticated and well-known current atomic models. Although it retains the nucleus concept from Bohr and Rutherford’s models, it provides a new description of electron velocity around the nucleus.

3. What gas makes up the cathode ray tube?

Hydrogen gas, the lightest gas (perhaps the lightest element) on ionisation, yields the highest charge value to the mass ratio (e / m ratio = \(1.76 \times {10^{11}}\) coulombs per kg), hence it is often used in cathode tube experiments.

Introduction 

When a phone is hooked to its charger, how does the battery work? How does the cell in a TV remote control work? All of these questions have been thoroughly explored in the scientific discipline of electrochemistry. Electrochemistry is the study of both the creation of electricity through chemical processes and the use of electricity to conduct non-spontaneous chemical reactions. The task is accomplished by using cells. Cells are the building blocks that trigger chemical processes that produce or generate electricity.

Types of cells

There are two types of cells:

1. Electrochemical cell: An electrochemical cell is a device that may produce electricity through chemical processes that occur naturally. The chemical reactions occurring here are called redox reactions. During redox reactions, electrons are exchanged between different chemical species. Galvanic or voltaic cells are other names for these devices. One type of electrochemical cell is the Daniell cell.
2. Electrolytic cell: Electrolytic cells are a subset of electrochemical cells that are capable of using electrical energy to catalyse chemical processes. That is to say; electricity needs to come from somewhere else. Then, an artificial reaction can be initiated. Electrolytic cells have traditionally been used for the electrolysis of substances.

Difference between electrochemical cells and electrolytic cells

Cell structure 

There are two electrodes in a cell: the cathode (positive) and the anode (negative) (-ve terminal). Submerge both electrodes in the corresponding metal salt solutions. The anode of an electrochemical cell is also known as the oxidation half-cell because of the chemical process that takes place there. The cathode is the decreased half-cell, another name for it. Connecting the two electrodes is a salt bridge, a U-shaped tube filled with gel and an electrolyte.

Daniel Cell Diagram

What is a Daniell cell?

An electrochemical cell known as a Daniell cell is used to transform chemical energy into electrical power. The cell undergoes a number of chemical processes in order to produce electricity. Electrodes made of zinc (Zn) and copper (Cu) are used as the anode and cathode in a Daniell cell. The salt solutions have been poured over the metals.

In a Daniell Cell, the anode is composed of zinc (Zn), while the cathode is composed of copper (Cu). There is still a chemical solution containing ions bathing both electrodes. The proper chemicals are copper sulphate and zinc sulphate. It improves the voltaic cell, using its copper and zinc electrodes to produce a 1.1 V potential difference. The cell supplies energy to the circuit after electrons are produced at the anode and transferred to the cathode.

Daniell cell chemical reaction 

The following chemical reactions take place in Daniell cell:

\(Zn\left( s \right) + C{u^{2 + }}\left( {aq} \right) \to Z{n^{2 + }}\left( {aq} \right) + Cu\left( s \right)\)

Reaction at the anode:

\(Zn\left( s \right) \to Z{n^{2 + {\rm{ }}}}\left( {aq} \right) + 2{e^ – }\;\;\;\)

Reaction at the cathode:

\(C{u^{2 + }} + 2{e^ – } \to Cu\left( s \right)\;\;\;\)

Daniell cell working 

In the Daniell Cell, \(CuS{O_4}\) and \({H_2}S{O_4}\)are stored in a copper container until needed. The components of its operating system are:

• A zinc rod that has crystallised in the zinc sulphate solution may be seen (\(Z{n_2}S{O_4}\)).
• A see-through layer underneath the copper container keeps the \(CuS{{O}_{4}}\) crystals and solution in touch. As a consequence, solution saturation is maintained.
• An electric current is produced by the external circuit.
• Mass is gained by the copper rod and lost by the zinc rod.
• Zinc sulphate concentration rises as Copper sulphate decreases.
• Both methods maintain their electrical neutrality.

Daniell cell representation 

The Daneil cell is represented as:

\(Zn{\rm{ }}\left| {{\rm{ }}Z{n^{2 + }}\left( {aq} \right){\rm{ }}} \right|{\rm{ }}\left| {{\rm{ }}C{u^{2 + }}\left( {aq} \right){\rm{ }}} \right|{\rm{ }}Cu\)

The symbol “| |” represent the salt bridge, the right side represents the reduction half-cell, and the left side refers to the oxidation half-cell.   

Application of Daniell cell 

Some of the applications of daniel’s cell are: 

• Used for making batteries, which are essentially just groups of cells in series.
• Creating electricity while minimizing electrical consumption.
• Telepathy through inductive coupling

Summary 

Certain electrochemical cells function in an electrolytic fashion. Hence, the electrolytic cell has everything that would normally be present in an electrochemical cell. Both electrochemical and electrolytic cells rely on the transport of electrons throughout the system to carry out their functions. Whereas electrolytic cells undergo non-spontaneous chemical reactions, electrochemical cells undergo chemical reactions of their own accord. To put it another way, an electrochemical cell is not the same as an electrolytic cell.

 

Frequently Asked Questions

1. What is a rechargeable cell?

Rechargeable batteries can only be made from secondary cells, which undergo reversible chemical processes. a cell that generates an electrical current, but whose chemical activity may be reversed by delivering a current in the opposite direction through the cell.

2. What maintains the electrical neutrality in a cell?

The Salt Bridge is responsible for preserving charge neutrality in the Daniell cell’s two compartments.  It is a glass tube which  contributes to keeping the balance of the charge.

3. Why are the charges of electrodes different in Daniel cell?

Daniel cell is an electrochemical cell whose anode has a negative potential with the solution. Which makes it negatively charged. The removal of the metals from the anode during oxidation causes a buildup of electrons upon that anode, which gradually turns it negative. Eliminating metal ions from the electrolyte results in the consumption of electrons, which turns the cathode positive.

Introduction

There is no such thing as an ideal gas in the real world; hence, the term “ideal gas” is strictly a theoretical one. An ideal gas is made up of several independently spinning, point-like particles that do not collide with one another in any way. Because it strictly adheres to the ideal gas law, the concept of this ideal gas (theoretical gas) has practical or theoretical significance (or ideal gas equation). The molecules in a real gas do not behave according to the ideal gas law or ideal gas equation because they occupy the necessary space and interact with one another. Because of the interactions between its molecules, cool air at standard pressure and temperature acts like an ideal gas. However, as its temperature and pressure increase, its behaviour changes to that of a real gas.

What is an ideal gas?

An ideal gas, sometimes known as a perfect gas, is a type of gas that has physical properties that are in perfect alignment with an idealised link between pressure, volume, and temperature. Ideal gases are also often referred to as perfect gases. They perfectly follow the different gas laws such as Charles’ law. It follows the ideal gas law which is as follows:

 PV = kT

where k is a constant. 

Properties of an ideal gas

General characteristics of an ideal gas are as follows-

1. Compressibility is one of the features of an ideal gas because its molecules have so much energy that they push each other closer together when compressed.
2. Most collisions in an ideal gas with its container are elastic, meaning the gas retains all or almost all of its original velocity after impact.
3. Because of their compressibility, perfect gases can assume the form of their storage vessel. The gas within the container has a total volume equal to the volume of the container itself.
4. It is often considered that perfect gases do not interact with one another because of their inert behaviour.
5. In an ideal gas, the individual molecules or particles are immobile, massless spheres.

Real and ideal gases characteristics

What is real gas?

In contrast to their ideal and non-ideal counterparts, real gases do not have molecules that fill space and interact with one another. In reality, gas does not behave according to the ideal gas law or ideal gas equation. Real gases are therefore developed, modelled, or represented further by factoring in their molar weight and molar volume.

The gas law for real gases is called the Vanderwall equation. It is written as

The variables a and b are determined empirically for individual gases. 

Properties of real gas

General characteristics of a real gas are as follows-

1. True gas has a measurable volume.
2. In a genuine gas, the vast majority of collisions are non-elastic, whether with the container or other gas molecules.
3. In a genuine gas, the molecules will interact with one another by either attractive or repulsive forces.
4. When compared to an ideal gas, the pressure exerted by the molecules inside this system is lower.
5. Molecules in a genuine gas can freely clash with one another.

Difference between Ideal gas and Real gas

Summary

The equation PV = nRT, known as the ideal gas law, describes the theoretical behaviour of ideal gases. The molecules of an ideal gas travel at fast speed and in all directions simultaneously. Particles here interact with one another by elastic collision, as intermolecular forces are absent. Non-ideal gases, which include actual gases, are so named because they defy the ideal gas law and equation. Particles in a real gas can collide with each other in a way that is not elastic because the molecules are moving in random directions and the pressure is lower than it would be in an ideal gas.

Frequently Asked Questions

1. What is the kinetic theory of gas?

The kinetic theory of gases makes use of an extremely large number of submicroscopic particles, such as atoms and molecules, in order to characterise the molecular composition of a gas. According to the hypothesis, particles hitting one other and the container walls create gas pressure. The kinetic theory of gases describes temperature, volume, pressure, viscosity, thermal conductivity, and mass diffusivity. It describes all microscopic qualities.

2. What do the constants “a” and “b” depend on in the van der waals equation?

To calculate the attractive forces between gas molecules, scientists use the van der Waals equation, where the constant ‘a’ indicates the strength of the forces and the constant ‘b’ reflects the effective volume filled by the gas molecules. You may also hear it referred to as co-volume or excluded volume.

3. What is the compressibility factor?

The compressibility factor (Z) is a measure of the capability of a gas to compress under external pressure. It is determined by dividing the molar volume of a gas to that of an ideal gas at a constant temperature and pressure. The compressibility factor is equal to one in the case of a perfect gas.

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.