Electronic Configuration: The distribution of electrons in an element’s atomic orbitals is described by its electron configuration. Atomic electron configurations follow a standard nomenclature in which all electron-containing atomic subshells are arranged in a sequence (with the number of electrons they possess indicated in superscript).

The three major subatomic particles present in an atom are protons, neutrons, and electrons. What are the electrons’ positions in the atom? What is the method of distribution? Do you know what the Bohr-Bury scheme is? What is an element’s capability for combining? Let’s look at the interesting facts covered in this article to find out the answers to these and other questions. Read further to find more.

What is Electronic Configuration?

Definition: The systematic distribution of electrons in the various atomic orbitals is called its electronic configuration. In the electronic configuration, electrons are distributed in various energy levels (various shells) of an atom, such as K shell, L shell, M shell, N shell, etc.

What is a Shell or Energy Level?

Atoms consist of \(3\) subatomic particles, namely positively charged protons, neutral neutrons, and negatively charged electrons. The protons and neutrons are located at the centre of the atom. The electrons revolve rapidly around the nucleus in fixed circular paths called energy levels or shells. The energy levels or shells are represented in \(2\) ways: either by the numbers \(1, 2, 3, 4, 5,\) and \(6\) or by the letters K, L, M, N, O or P. The energy levels are counted from the centre to outwards. Each energy level or shell is associated with a fixed amount of energy. The shell nearest to the nucleus has minimum energy and the cell farthest from the nucleus has the maximum energy.

I am Sodium with Atomic Number \(11.\) How Many Electrons Do I Have?

In a neutral atom, the number of protons is equal to the number of electrons in it. Therefore, an atomic number of an element is equal to the number of electrons in a neutral atom of that element.

Atomic number of an element \(\left( {\rm{Z}} \right)\) Number of electrons in one neutral atom.

For example, one neutral atom of sodium contains (11) electrons, so the atomic number of sodium is (11.)
The atomic number is not equal to the number of electrons in an ion because only a neutral atom contains an equal number of protons and electrons. Since the ion is formed by the removal of electrons from a normal atom or by the addition of electrons to a normal atom. A positively charged ion formed by the removal of the electrons is called cation whereas a negatively charged ion formed by the gain of electrons is called an anion.
The atomic number and mass number can be indicated on the symbol of an element. The atomic number is written on the lower side of the symbol, whereas the mass number is written on the upper side of the symbol of the element.

Example: Representation of carbon \({}_6^{12}{\rm{C}}\)

The total number of protons and neutrons present in one atom of an element is known as its mass number. That is,

Mass number \(\left( {\rm{A}} \right){\rm{ = }}\) Number of protons + Number of neutrons.

Learn About Alkali Metals

Bohr-Bury Scheme for Electronic Configuration

Electron shell	Value of n	Maximum capacity of electron \(\left( {{\rm{2}}{{\rm{n}}^{\rm{2}}}} \right)\)
K shell	\(1\)	\(1\) electrons
L shell	\(2\)	\(8\) electrons
M shell	\(3\)	\(18\) electrons
N shell	\(4\)	\(32\) electrons

2. The outermost shell of an atom cannot accommo

date more than \(8\) electrons, even if it has the capacity to accommodate more electrons. It is because “having \(8\) electrons in the outermost shell” makes the atoms very stable. But helium is an exception as it has only \(2\) electrons in the outermost shell. For example, if the \({\rm{M}}\) shell is the outermost shell of an atom, it can hold a maximum of \(8\) electrons only; but its maximum capacity is \(18\) electrons. These electrons in an atom do not occupy a new shell unless all the inner shells are completely filled with electrons. This means that the electron shells in an Atom are filled in a stepwise manner.

Atomic Structure of Elements

Atomic structure of an element shows the structure of the atom comprising the nucleus and the arrangement of electrons around the nucleus.

Atomic Structure of Magnesium \(\left( {{\rm{Mg}}} \right)\):

Magnesium has \(12\) protons and \((24 – 12) = 12\) neutrons. The number of protons is equal to the number of electrons, i.e., \(12.\) Thus, the electronic configuration of magnesium is:

K	L	M
\(2\)	\(8\)	\(2\)

The distribution of electrons in different shells on an atom is represented as follows,

The structure of the magnesium atom

Electronic Configuration of First 20 Elements

What do you call Electrons in the Outermost Shell?

The outermost shell of an atom is called its valence shell, and the electrons present in the valence shell are known as valence electrons. Example: The electronic configuration of carbon \((6)\) is \(2, 4.\) In carbon, there are \(4\) electrons in the L shell; therefore, valence electrons in the carbon are \(4.\)

What is Valency?

Valency of an element is the combining capacity of that element with other elements and is equal to the number of electrons taking part in a chemical reaction. The valency of elements having \(1, 2,\) or \(3\) valence electrons is \(1, 2,\) or \(3\) respectively, while the valency of elements with \(4, 5, 6,\) and \(7\) valence electrons is \(4, 3, 2,\) and \(1\) (\(8\) minus valence electrons) respectively. The valency of an element with \(8\) valence electrons is zero, it is stable as its valence shell is completely filled.

Position of Element and Electronic Configuration

Valence electrons indicate the group number of elements in the modern periodic table, and shell number indicates the period number.

Example 1: Electronic configuration of magnesium, Mg \((12)=2, 8, 2.\)
There are \(2\) electrons in the valence shell; hence the group number is \(2,\) and the valence electrons in the M-shell \(\left( {{\rm{n = 3}}} \right).\) Therefore, it is placed in the \({\rm{3rd}}\) period.

 

Note: If the valence electron is more than \(2,\) then add \(10\) to the valence electron to find the group number.

 

Example 2: Electronic configuration of phosphorus,\({\rm{N}}\left( {\rm{7}} \right){\rm{ – 2,5}}{\rm{.}}\)
There are \(5\) electrons in the valence shell; hence the group number is \(15,\) and the valence electrons in the L-shell \(\left( {{\rm{n = 2}}} \right).\) Therefore, it is placed in the \({\rm{2nd}}\) period.

Is Electronic Configuration of \({\rm{Na}}\left( {{\rm{11}}} \right){\rm{ – 1}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{p}}^{\rm{6}}}{\rm{,\;3}}{{\rm{s}}^{\rm{1}}}\) correct?

The electronic configuration of different atoms can be represented as \({{\rm{s}}^{\rm{a}}}{\rm{,}}{{\rm{p}}^{\rm{b}}}{\rm{,}}{{\rm{d}}^{\rm{c}}}{\rm{,}}{{\rm{f}}^{\rm{d}}}\)

In the ground state of an atom, the electrons are added progressively to the various orbitals in the increasing order of energies starting from the orbital of lowest energy (This rule is called the Aufbau principle).

The increasing order of energies of various orbitals is:

\({\rm{1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, \ldots }}\)

The maximum number of the electron that can accommodate in s, p, d and f orbital is as follows:

Orbital	Maximum number of electrons
s	\(2\)
p	\(6\)
d	\(10\)
f	\(14\)

Example 1: The electronic configuration of sodium:
Atomic number of sodium is \(11.\) It contains \(11\) electrons.
The electronic configuration of sodium, \({\rm{N}}\left( {11} \right){\rm{ – 1}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{p}}^{\rm{6}}}{\rm{,\;3}}{{\rm{s}}^{\rm{1}}}\)

Example 2: The electronic configuration of calcium.
Atomic number of calcium is \(20.\) It contains \(20\) electrons.
The electronic configuration of calcium,
\({\rm{Ca}}\left( {{\rm{20}}} \right){\rm{ = 1}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{p}}^{\rm{6}}}{\rm{,\;3}}{{\rm{s}}^{\rm{2}}}{\rm{,\;3}}{{\rm{p}}^{\rm{6}}}{\rm{,\;4}}{{\rm{s}}^{\rm{2}}}\)

Example 3: The electronic configuration of chromium.
Atomic number of chromium is \(24.\) It contains \(24\) electrons.
The expected electronic configuration of chromium,
\({\rm{Cr}}\left( {{\rm{24}}} \right){\rm{ – 1}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{p}}^{\rm{6}}}{\rm{,\;3}}{{\rm{s}}^{\rm{2}}}{\rm{,\;3}}{{\rm{p}}^{\rm{6}}}{\rm{,\;4}}{{\rm{s}}^{\rm{2}}}{\rm{,\;3}}{{\rm{d}}^{\rm{4}}}\)
The actual electronic configuration of chromium,
\({\rm{Cr}}\left( {{\rm{24}}} \right){\rm{ – 1}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{p}}^{\rm{6}}}{\rm{,\;3}}{{\rm{s}}^{\rm{2}}}{\rm{,\;3}}{{\rm{p}}^{\rm{6}}}{\rm{,\;4}}{{\rm{s}}^{\rm{1}}}{\rm{,\;3}}{{\rm{d}}^{\rm{5}}}\)
This is because half-filled and completely filled orbitals have more stability. Therefore, in chromium, one electron from 4s-orbital is shifted to the 3d- orbital.

Example 4: The electronic configuration of copper.
Atomic number of copper is \(29.\) It contains \(29\) electrons.
The expected electronic configuration of copper,
\({\rm{Cu}}\left( {{\rm{29}}} \right){\rm{ – 1}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{p}}^{\rm{6}}}{\rm{,\;3}}{{\rm{s}}^{\rm{2}}}{\rm{,\;3}}{{\rm{p}}^{\rm{6}}}{\rm{,\;4}}{{\rm{s}}^{\rm{2}}}{\rm{,\;3}}{{\rm{d}}^{\rm{9}}}\)
The actual electronic configuration of copper,
\({\rm{Cu}}\left( {{\rm{29}}} \right){\rm{ – 1}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{p}}^{\rm{6}}}{\rm{,\;3}}{{\rm{s}}^{\rm{2}}}{\rm{,\;3}}{{\rm{p}}^{\rm{6}}}{\rm{,\;4}}{{\rm{s}}^{\rm{1}}}{\rm{,\;3}}{{\rm{d}}^{{\rm{10}}}}\)
This is due to the extra stability of a completely filled orbital.

Summary

By assisting in the determination of an atom’s valence electrons, electron configurations give insight into the chemical behaviour of elements. It also helps in the classification of components into separate blocks (such as the s-block elements, the p-block elements, the d-block elements, and the f-block elements). This makes it easy to investigate the characteristics of the components as a group.

The systematic distribution of electrons in the various atomic orbitals is called its electronic configuration. In this article, we learned in detail about Electronic Configuration, shells or energy levels, and atomic structure. The outermost shell of an atom is called its valence shell, and the electrons present in the valence shell are known as valence electrons. We also learned what is valency with examples and the position of the element and electronic configuration. Here, we have also provided you with an electronic configuration of the first 20 elements for your reference.

PRACTICE QUESTIONS RELATED TO ELECTRONIC CONFIGURATION

Electronic Configuration – Frequently Asked Questions

Q.1. Explain why sodium ion \(\left( {{\rm{N}}{{\rm{a}}^{\rm{ + }}}} \right)\) has completely filled K and L shells?
Ans: A sodium ion has \(10\) electrons in it because \({{\rm{N}}{{\rm{a}}^{\rm{ + }}}}\) ion is formed by donating one electron. Now the maximum capacity of the K shell is \(2\) electrons, and that of the L shell is \(8\) electrons. Taken together, the maximum capacity of K and L shells is \(2+8=10\) electrons. A sodium ion has completely filled K and L shells because its \(10\) electrons can completely fill up the K and L shell.

Q.2. How do you find the electronic configuration?
Ans: The electronic configuration is written by using the Bohr-Bury scheme. According to this, the maximum number of electrons that can be accommodated in any energy level of an atom is given by \({\rm{2}}{{\rm{n}}^{\rm{2}}}{\rm{,}}\) where \(n\) is the number of that energy level.
Example: Electronic configuration of aluminium. \({\rm{Al }}\left( {{\rm{13}}} \right){\rm{ – 2, 8, 3}}{\rm{.}}\)

Q.3. What is the electronic configuration of element \(17\)?,
Ans: The configuration of element \(17\) is \({\rm{K}}\left( {\rm{2}} \right){\rm{,L}}\left( {\rm{8}} \right){\rm{,M}}\left( {\rm{7}} \right){\rm{.}}\) The element is chlorine.

Q.4. What is the so-called electronic configuration?
Ans: The systematic distribution of electrons in various energy levels of an atom of an element is called its electronic configuration.

Q.5. What is the electronic configuration of element \(14\)?
Ans: The configuration of element \(14\) is \({\rm{K(2), L(8), M(4)}}{\rm{.}}\)
The element is silicon. The electronic configuration is also written as \({\rm{1}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{p}}^{\rm{6}}}{\rm{,\;3}}{{\rm{s}}^{\rm{2}}}{\rm{,\;3}}{{\rm{p}}^{\rm{2}}}{\rm{.}}\)

Q.6. What is the electronic configuration of element \(27\)?
Ans: The configuration of element \(27\) is
\({\rm{1}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{p}}^{\rm{6}}}{\rm{,\;3}}{{\rm{s}}^{\rm{2}}}{\rm{,\;3}}{{\rm{p}}^{\rm{6}}}{\rm{,\;4}}{{\rm{s}}^{\rm{2}}}{\rm{,\;3}}{{\rm{d}}^{\rm{7}}}.\) The element is cobalt.

Q.7. Why are electronic configurations important?
Ans: The electronic configuration gives details about the chemical properties of elements. Elements with the same number of valence electrons have the same chemical properties. Based on this these elements are placed in the same group in the modern periodic table.

Q.8. Write the electronic configuration of copper?
Ans: Electronic configuration of chromium,
\({\rm{Cu}}\left( {{\rm{29}}} \right){\rm{ – 1}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{p}}^{\rm{6}}}{\rm{,\;3}}{{\rm{s}}^{\rm{2}}}{\rm{,\;3}}{{\rm{p}}^{\rm{6}}}{\rm{,\;4}}{{\rm{s}}^{\rm{1}}}{\rm{,\;3}}{{\rm{d}}^{{\rm{10}}}}.\)
This is due to the extra stability of a completely filled orbital. Therefore, one electron from 4s-orbital is shifted to the 3d-orbital.

Q.9. How do you set up electronic configuration?
Ans: In the ground state of an atom, the electrons are added progressively to the various orbitals in the increasing order of energies starting from the orbital of lowest energy (This rule is called the Aufbau principle). The increasing order of energies of various orbitals is:
\({\rm{1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, \ldots }}\)
Example: Electronic configuration of sulphur, \({\rm{S}}\left( {{\rm{16}}} \right){\rm{:1}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{s}}^{\rm{2}}}{\rm{,\;2}}{{\rm{p}}^{\rm{6}}}{\rm{,\;3}}{{\rm{s}}^{\rm{2}}}{\rm{,\;3}}{{\rm{p}}^{\rm{4}}}\)

 

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