Electronic Configuration in Periods and Groups

Electronic Configuration is the arrangement of electrons in orbitals around an atomic nucleus. Electronic Configuration of a molecule refers to the distribution of electrons in various molecular orbitals. The number of electrons in bonding and antibonding molecular orbitals of a molecule or molecular ion can be calculated from its electronic configuration.

In this article, we will learn about Electronic Configuration, Electronic Configuration in Periods, and Electronic Configuration in Groups.

What is Electronic Configuration?

Electronic Configuration refers to the arrangement of electrons among the orbitals of an atom or molecule. Electronic configurations are typically produced by conventional notation (especially for elements having a relatively large atomic number). In such instances, a shortened or condensed notation may be employed instead of the normal notation. In shortened notation, the sequence of entirely filled subshells that correspond to a noble gas’s electronic configuration is replaced by the noble gas’s symbol in square brackets. 

As a result, sodium’s abbreviated electron configuration is [Ne] 3s¹ (the electron configuration of Neon is 1s² 2s² 2p⁶, which can be abbreviated to [He] 2s² 2p⁶.

Electronic Configuration Definition

Electronic configuration is defined as the arrangement of electrons at different energy levels around an atomic nucleus.

Electronic Configuration allows us to know the number of electrons present in the outermost shell, hence, as a result, electron configurations can be used for the following purposes:

• Determining an Element’s Valency
• Predicting the qualities of a group of elements (elements with similar electron configurations tend to exhibit similar properties).
• The interpretation of Atomic Spectra, etc.

Electronic configuration provides a structured way of representing the arrangement of electrons within an atom, indicating the energy levels and sublevels they occupy.

Electronic Configuration in Periods

Electronic configuration of the elements in periods can be found by using following points:

• The period of the element is the value of n, the primary quantum number, for the valence shell.

• The number of electrons that can be accommodated by different energy levels varies.

• The maximum number of electrons that can be accommodated in an energy shell is given by 2n², where n is the energy level. It is the greatest number of electrons that a given energy level can allow. So the first energy level (K shell) can hold up to 2 electrons, the second (L shell) up to 8 electrons, the third (M shell) up to 18 electrons, and so on.

• The second period begins with Lithium and Beryllium, both of which have three and four electrons, respectively, and so the final electrons reach level two.

• The third period begins with Sodium and finishes with Argon, filling the 3s and 3p orbitals in that order. There are eight elements in this period as well.

• The level 4s are filled first in the fourth period with n = 4. It all starts with potassium. However, we know that the 3d orbital must be full before the 4p orbital can be filled. Scandium is the first of the 3d transition elements. The 3d orbital gets completely filled with electrons in the case of zinc.

• The level 5s are filled first in the fifth period with n = 5. The 4d transition series, which begins with the Yttrium, dominates this time. The 5p orbital is completely filled by Xenon at the end of the period.

• With n = 6, the sixth period has 32 elements, with electrons filling the 6s, 4f, 5d, and 6p orbitals. Cerium signifies the entry of electrons into the 4f orbital, resulting in the lanthanide series of 4f-inner transition elements.

• The radioactive elements with electrons filling the 7s, 5f, 6d, and 7p orbitals belong to the seventh period with n = 7. Similar to period 6, this period causes electrons to fill the 5f orbital, giving rise to the actinide series of 5f-inner transition elements.

Electronic Configuration in Groups

The outermost shells of elements in the same group have the same number of electrons, resulting in identical valence shell electrical configurations. As a result, the characteristics and chemistry of elements in the same group follow a similar pattern.

An example of the electronic configuration of elements in the same group is, Lithium(Li) and Sodium(Na) both are in the same group thus, their electronic configuration is,

• Lithium (LI) = [He] 2s¹
• Sodium (Na) = [Ne] 3s¹

Filling of Atomic Orbitals

We fill the atomic orbital with the electrons in accordance with these three rules,

• Aufbau Principle
• Pauli Exclusion Principle
• Hund’s Rule

i.e. these three rules guide us to fill electrons in the atomic orbitals. Now, let’s learn about them in detail.

Aufbau Principle

The name of the Principle Aufbau is taken from the German word Aufbeen, which means “to build up”. According to the Aufbau Principle, electrons will occupy lower energy orbitals before moving on to higher energy orbitals. The energy of an orbital is calculated by adding its Primary quantum Number(n) and Azimuthal Quantum Number(l) or using the (n+l) rule.

According to this principle, electrons are filled in the following order: 

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

There are a few exceptions to the Aufbau Principle, such as Chromium and Copper. These exceptions can occasionally be explained by the stability offered by half-filled or fully-filled subshells.

Aufbau Principle

Pauli Exclusion Principle

According to the Pauli Exclusion Principle, an orbital can only hold a maximum of two electrons with opposite spins, i.e. no two electrons in the same atom have the same values for all four quantum numbers in an orbital.

As a result, if two electrons have the same Principle, Azimuthal, and Magnetic numbers, they must have opposite spins.

Hund’s Rule

Hund’s Rule specifies the order in which electrons are filled in all subshell orbitals. Hund’s Rule rule states that every orbital in a particular subshell is occupied by an electron before a second electron enters the subshell.

The electrons in orbitals with only one electron all have the same spin to maximize the total spin (or the same values of the spin quantum number).

Representation of Electronic Configuration

Electronic configuration of an atom is represented using a standardized notation system that indicates the distribution of electrons among the various atomic orbitals. Electronic Configurations are represented as follows:

• Shell Designation: Each electron shell is represented by a number ‘n’, where n= 1, 2, 3,….. This number corresponds to the principal quantum number.
• Subshell Designation: Each shell is further divided into different subshell that are represented using the notation of subshells (s, p, d, f).
• Orbital Filling Order: Electrons are then filled in orbitals from lowest energy orbital to highest according to Aufbau Principal. According to this principle, electrons are filled in the following order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.
• Electron Count: Number of electrons occupying each orbital is indicated by a superscript following the orbital designation. For example, 1s² represents that 1s orbital contains 2 electrons.

Writing Electron Configuration

For Writing Electron Configuration of an element, we must know the basic information about the element like atomic number, no. of electrons, shells, etc. The electronic configuration is typically represented using the notation of subshells (s, p, d, f) and the number of electrons in each subshell. For example, the potassium element has atomic number 19. And has 19 electrons which will be placed in s and p sub-shell. 

The electronic configuration can be written as 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹. Its 19 electrons can be divided into different shells in a manner,

• K shell (n = 1) = 2,
• L shell (n = 2) = 8,
• M shell (n = 3) = 8, and
• N shell (n = 4) = 1.

Electronic Configurations of First 20 Elements

The electronic configuration of the first twenty elements of the periodic table is shown in the table added below,

Read More,

• Periodic Classification of Elements
• Alkali Metals
• Electronic Configuration of the d-block Elements

Electronic Configuration: Frequently Asked Questions

What is Electronic Configuration of an Element?

Electronic Configuration of an element is the symbolic representation of how the electrons of that atoms are arranged across different atomic orbitals.

What are Three Rules used while Writing Electronic Configuration of Elements?

The three rules used in filling the atomic orbital or writing the Electronic configuration of an elements are,

1. Aufbau Principle
2. Pauli’s Exclusion Principle
3. Hund’s Rule of Maximum Multiplicity

How are Groups and Periods related to Electron Configuration?

Groups are determined by the number of valence electrons and periods are determined by the number of electron shells.

Why are Electronic Configurations of an Element Important?

Electron configurations of an element is important because it provide insight into the chemical behavior of elements by assisting in the determination of an atom’s valence electrons. It also helps in separating elements into four different blocks,

• s-block
• p-block
• d-block
• f-block

This makes studying various elements easy.

What is Pauli Exclusion Principle?

Pauli’s Exclusion Principle states that, an orbital can only hold a maximum of only two electrons with opposite spins, i.e. one with clockwise spin, and other with anti-clock wise spin.

Define Electronic Configuration.

Electronic configuration of an atom refers to the distribution of its electrons among the various atomic orbitals.

What is Hund’s Rule of Maximum Multiplicity?

Hund’s Rule of Maximum Multiplicity or simply Hund’s Rule specifies the order in which electrons are filled in all of a subshell’s orbitals.

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