Electronic Configuration of Elements and Stability of Orbitals

Introduction

An atom's electrical configuration is determined by how its electrons are arranged in orbitals and shells. The energy required to remove an e^- from an atom is what determines whether an orbital is stable. An orbital is more stable the higher its energy level.

The quantity of protons there in the nucleus determines the electronic structure of an atom. The atomic no. of an atom is based on how many protons are present in its nucleus. The no. of electrons in an atom is also based on how many protons are present in its nucleus.

Standard Notation of Electron Configuration

Electron configuration notation, which lists the elements in ascending atomic number order and then lists the e- in orbitals, from lowest to highest energy level, is used to represent the electron configuration of an atom. Carbon, for instance, has the electron configuration 1s² 2s² 2p².

The element's atomic number is indicated by the first number in the notation for the electron configuration. The no. of electrons in the 1st energy level is indicated by the 2nd number in the notation. The number of electrons in the 2nd energy level is indicated by the 3rd number in the notation. So forth.

Atomic Orbitals

Electron motions are more intricate than they appear. They always adhere to a set of predetermined routes known as orbitals or subshells. These orbitals come in a variety of forms, including s, p, d, and f. If so, the 1st energy level is the only one with an s orbital, while the second one has an s and three p orbitals. Like the second energy level, the third has five d orbitals and three p orbitals. The lowest energy orbital out of all of them is s.

• A total of two electrons can be accommodated in each type of orbital.

• The nucleus is encircled by the s orbital, which has a sphere-like form. The p orbital has two lobes and is formed like a dumbbell. A four-lobed orbital makes up the d orbital.

• In an atom, electrons first occupy orbitals with the lowest energies. An atom's electrons first occupy the s orbital, then the p orbital, and finally the d orbital. The s orbital has two electrons, while the p orbital has six.

haade, Single electron orbitals, CC BY-SA 3.0

Electronic configuration rule

An atom's electron configuration is determined by how its electrons are arranged in its outer and inner shells. The electron configuration rules can be applied to determine the e- configuration of an atom.

Four principles govern electron configuration −

• Electrons always inhabit the lowest possible energy levels first, according to the first rule.

• By the second rule, electrons occupy shells before subshells.

• The third rule states that a shell can only contain a maximum of two electrons.

• The fourth rule states that a subshell can only contain a maximum of eight electrons.

The rules for determining electron configuration can be applied to an atom. Determine how many shells there are as a first step. The quantity of protons in the nucleus affects how many shells there are. Calculating the number of subshells is the second stage. The number of electrons an atom contains determines how many subshells it has. Finding out how the atoms' electron configurations are organised within every shell and subshell is the third stage.

Aufbau rule

The Aufbau principle states that the electron fills its ground state in ascending energy order. As opposed to the higher energy state, the atomic orbital having the lowest energy level was occupied first.

• The Aufbau principle states that the electron with the lowest energy occupies the place first.

• The n + 1 rule can be used to calculate the energy of orbital growth. The various energy levels of the orbitals are determined by the sum of the principal and mutual quantum numbers.

• Lower orbital energy is associated with lower n+1 values. The orbital with the lower n number is regarded as having lesser energy if two orbitals have the same n+1 value.

• Electrons are filled in the following order: 1s, 2s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, etc.

Hund's rule

According to Hund's rule, coupling of electrons in orbitals with the same subshell doesn't happen until each orbital in that subshell has one electron, at least. When there are three p, five d, and seven f orbitals, for instance, electron pairing begins with the f, d and p orbitals with the eighth, sixth and fourth electron

When the electrons in these orbitals are filled, the sublevel containing the two electrons in each orbital is first filled with one electron with the same spin. The e- field doubles with the opposite polarity in each level once all sublevels have been completed. For instance, the p orbital, having 3 subshells, will have three electrons in a field with the same spin, and the remaining three electrons will be placed one at a time in the sublevels with the opposite spin.

Paul exclusion principle

Pauli's Exclusion Principle states that no two atom's electrons can have the same set of 4 quantum numbers. There can only be two electrons in a single orbital, and they must have the opposite spin.

Pauli's Exclusion principle has two rules −

• The same orbital is occupied by two electrons.

• Two electrons in the very same orbital possess antiparallel spins or opposite spins.

In addition to electrons, other entities like half-integer spin are also subject to Pauli's Exclusion principle.

What is a stable electronic configuration?

An atom's stability can be predicted by its electron arrangement. All an atom's orbitals must be occupied for it to be the most stable and unreactive. A most stable electron form also has a fully charged state of energy. Noble gases have a lot of these orbital configurations, which makes it difficult for them to easily combine with other chemicals.

Whenever two or more atoms come into touch with one another, the valence shells, or the outer electrons of an atom, are what initially interact. The most stable state of an atom occurs when its valence shell is filled. The valence electrons control an element's chemical behaviour. For instance, elements with equivalent valence electrons exhibit comparable chemical characteristics.

Configuration of anion and cations

Ions are atoms (or collections of atoms) with an electric charge because of gaining or losing 1 or more electrons. A negative charge is added to an atom when it obtains electrons. It turns positively charged if electrons are lost.

Create the neutral atom's electrical structure, then add (for a -ve ion) or eliminate (for a +ve ion).

• -ve ion

  $$\mathrm{Cl: 1s^2 2s^2 2p^6 3s^2 3p_x^2 3p_y^2 3p_z^1,\: but\: Cl^-\: has\: one\: more\: electron}$$

  $$\mathrm{ Cl^-: 1s^2 2s^2 2p^6 3s^2 3p_x^2 3p_y^2 3p_z^2}$$

• +ve ion

  $$\mathrm{Ca: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2,\: but\: Ca^{2+}\: has\: two\: less\: electrons}$$

  $$\mathrm{Ca^{2+}: 1s^2 2s^2 2p^6 3s^2 3p^6}$$

Conclusion

The octet electronic configuration of noble gases is known as a noble gas configuration. The propensity of chemical elements to gain stability serves as the foundation for all chemical reactions. When chemical bonds are formed between some main group elements, a standard electronic configuration that resembles a noble gas is frequently the result.

Every system tends to reach a stable or low-energy state, which is why chemical elements participate in chemical reactions to achieve a stable electronic configuration resembling that of the nearby noble gas.

FAQs

1. How can you tell if a substance is stable?

If the forces between the constituents of the nucleus are equal, an atom is stable. If such forces are out of balance or the nucleus has too much internal energy, an atom is unstable. An overabundance of neutrons or protons can make the nucleus of an atom unstable.

2. What causes 5D to fill before 4F?

In order of energy, orbitals fill. Because the 5D energy levels are sometimes lower than the 4F levels, 5D fills earlier than 4F in some situations. The lanthanides do not all experience this.

3. Why does a stable shell with 8 electrons form?

Because their electrical structure is comparable to that of the nearest noble gas, atoms with eight e^- in their valence shell have filled outermost orbitals and are hence the most stable.

4. What atoms can sustain valence electron counts of less than eight?

Octet norms are generally followed by atoms, however, there are occasional exceptions. For instance, elements like boron or beryllium frequently produce compounds (like BF₃or BeH₂) in which the core atom is surrounded by less than eight electrons.

5. What makes noble gases stable?

Given that these atoms' complete valence electron shells make them exceedingly stable and reduce their propensity to receive or lose electrons, noble gases are also highly incapable of having chemical bonds.