Tag: Hund’s rule

Introduction

Aufbau is a German word that means “building up.” Like a construction build-up from the ground up. Atoms are also filled with electrons in this manner. An atom has orbitals that are arranged in increasing energy level order. According to the Aufbau principle, electrons are filled in the order of increasing energy of the atomic orbitals. That is from the bottom to the top. This principle aids in the electronic configuration of atoms as well as the placement of electrons in orbitals. In all atoms, the orbital is always the first orbital to be filled with electrons. After filling this orbital, electrons are filled in orbitals further away.

Explain Aufbau Principle

Niels Bohr, a Danish physicist developed the principle. According to this principle, the increasing order of energy levels of atoms causes the filling of electrons in an atom. They are entering a perfect order that corresponds to the energy level of orbitals.  We can predict the electron configurations of atoms or ions by using this rule.

The Madelung rule or rule is also related to this rule. According to this rule, the filling of electrons in an atom occurs as the value of n+l increases. That is, the electrons are filled to a lower-valued orbital. Where n represents the principal quantum number value, and l represents the angular momentum quantum number value. This is known as the Madelung rule or the diagonal rule.

Some features of the Aufbau Principle

1. Electrons are assigned to the subshell with the lowest energetically available energy.
2. An orbital can only hold two electrons.
3. If two or more energetically equivalent orbitals (e.g., p, d, etc.) are available, electrons should be spread out before being paired up (Hund’s rule).

Some Exceptions 

Some elements exhibit exceptional behaviour in terms of the Aufbau principle. They are chromium and copper, respectively. According to the Aufbau principle, the electronic configuration of chromium is \(\left[ {Ar} \right]3{d^4}4{s^2}\). However, chromium’s electronic configuration is \(\left[ {Ar} \right]3{d^5}4{s^1}\). And this is because chromium achieves stability by having a half-filled orbital. Elements require a filled state at all times. A fully-filled orbital is always more stable. Even though a half-filled orbital has partial stability.

Copper’s electronic configuration is \(\left[ {Ar} \right]{\rm{ }}3{d^{10}}4{s^1}\) rather than \(\left[ {Ar} \right]{\rm{ }}3{d^9}4{s^2}\). This is due to the presence of a fully-filled d-orbital configuration, which provides additional stability.

Summary

An electronic configuration is present for all elements to locate electrons in orbitals. As a result, the chemical properties of elements can be explained. When combined with other rules, this can result in a proper electronic configuration. According to Aufbau’s principle, the filling of electrons in an atomic orbital occurs in the order of increasing energy of atomic orbitals. The elements chromium and copper are exceptions to this rule. Because they achieve a half-filled and fully-filled atomic orbital, these elements can be more stable.

Frequently Asked Questions

1. Define Hund’s rule of maximum multiplicity

For an orbital of the same sub-shell, the filling of electrons takes place in a way that all the electrons are singly occupied before pairing occurs. The pairing of electrons takes place only when all the subshells are singly occupied.

2. What do you understand by Pauli’s exclusion principle?

All the quantum number values are distinct for each electron present in an atom. This principle states that no two electrons in an atom can have an equal set of all the quantum number values. And thereby we can easily locate all the electrons in an atom.

3. What is the principal quantum number?

The number that deals with the energy and size of orbitals are a principal quantum number. It will explain how far an electron is from the nucleus. For example, the electronic configuration of Helium is \(1{s^2}\) so the principal quantum number is 1.

Introduction

The electronic configuration describes the distribution of electrons within an atomic subshell. An electron configuration is a summary of the prediction of the position of the electrons surrounding a nucleus. In every neutral atom, the electron number is the same as the proton number. Now we’ll arrange those electrons so that they form a ring around the nucleus, displaying their energy and the orbital type in which they are located. Electrons occupy orbitals in a specific order based on their energy.

What do you understand by Electron Configuration?

• The electronic configuration describes the distribution of electrons within an atomic subshell.
• Atomic electronic configurations follow a standard format in which each atomic subshell containing an electron is listed in ascending order.
• For high atomic numbers, the standard representation of electronic configuration can be quite lengthy. In some cases, an abbreviated/condensed symbol may be used instead of the standard representation.
• The electron configuration of Na, for example, is \(1{s^2}2{s^2}2{p^6}3{s^1}\).

How Subshells are important for Electron Configuration?

• The azimuthal quantum no., represented by the letter “l,” determines the distribution of electrons into subshells.
• The magnitude of the principal quantum no., n, dictates the magnitude of this quantum number. As a result, when n equals 4, four distinct subshells can exist.
• For n = 4, the s, p, d, and f subshells correspond to l=0, 1, 2, 3 quantities.
• Equation 2(2l+1) gives the maximum number of electrons that a subshell can hold.
• The s, p, d, and f subshells can hold a maximum of 2, 6, 10, and 14 electrons, respectively.

Atomic Electronic Configuration Representation

This section provides examples of a few elements’ electronic configurations.

• The electron configuration of hydrogen has an atomic number of one. As a result, an H atom has one electron, which will be assigned to the subshell of the first shell/s orbit. \(1{s^1}\) is the electronic configuration of H.
• The electron configuration of chlorine

Cl has the atomic number 17. As a result, its 17 electrons are distributed as follows:

The K has two electrons.

The L has 8 electrons and the M has 7 electrons.

The electron configuration of Cl is depicted below. It is written as \(1{s^2}2{s^2}2{p^6}3{s^2}3{p^5}\).

Filling Atomic Orbitals

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

Aufbau Principle

“The energy of an atomic orbital is calculated by adding the principal and azimuthal quantum numbers, and according to the Aufbau principle, electrons begin in relatively low energy orbitals and progress to higher energy orbitals.”

Pauli Exclusion Principle

“Only electron pairs with opposite spins can be carried in an atomic orbital, and no two electrons in the same atom have the same values for all four quantum numbers. If two electrons have the same principle, azimuthal, and magnetic numbers, they should have opposing spins.”

Hund’s Law

“Before a second electron is placed in an orbital, each orbital in a specific subshell is said to be entirely filled by electrons.”

Summary

It can be concluded that Electron configuration is the depiction of electron distribution inside an element’s atomic shells. Because the electrons are mathematically positioned in these subshells, the configuration aids in determining their position. The periodic table categorises elements based on their electron configurations. These make up the s, p, d, and f-block elements. The maximum number of electrons that can fit in a shell is determined by the principal quantum number (n). The azimuthal quantum number, represented by the letter “l,” governs the distribution of electrons into subshells.

Frequently Asked Questions

1. Why are specific electron configurations required for elements?
Ans. Electron configurations can shed light on an atom’s chemical behaviour by identifying its valence electrons. It also aids in the organisation of elements into different blocks such as s, p, d, and f blocks.

2. Describe the significance of electron configuration.
Ans. The significance is as follows:

They aid in determining the reactivity state of an atom.

It aids in the identification of both chemical and physical properties.

It foretells an atom’s magnetic properties.

3. For n=3, which subshells are present?
Ans. Each orbital can hold a maximum of two electrons, and there are four subshells present- s, p, d, and f for n=3. The maximum number of orbitals corresponding to the s, p, d, and f subshells is 1,3,5, and 7.