Calculation of Valence Electrons

To calculate the number of valence electrons in an atom, you can use the following methods:

Periodic Table Method

For s-block elements, the number of valence electrons is equal to the group number on the periodic table. For p block elements, the number of valence electrons is equal to the group number minus ten. For example, the valence electron of aluminium is 13 – 10 = 3. This method makes the valence electrons of the main group elements directly determinable.

Valence electrons of s and p block elements

The valence electrons of the elements belonging to s and p block are mentioned below:

For example, when you want to know how many valence shell electrons the sodium (Na) has, you can see in the periodic table that it belongs to Group 1. Thus, sodium gets a valence electron that is one. Besides, similarly to find out the valence electrons of the element nitrogen N, you only need to observe that it is at Group 15 on the periodic table or Group V. Nitrogen therefore has five electrons in its valency.

Valence Electron for Transition Elements

In case of transition elements, it is slightly difficult to determine the number of valence electrons using periodic table. However, we can get range of valence electrons from the table below

Electronic Configuration Method

This technique takes into account the electron distribution of the atom and counts the number of electrons at the highest energy level, which can be termed the valence shell. When counted, one can determine the valence electron in any atom by obtaining a clear view of its electron configuration.

For example, if we need to find the electronic configuration of Oxygen then we need to write its electronic configuration. The atomic number of oxygen is 8, hence using Aufbau Principle, Pauli Exclusion Principle and Hund’s rule, we can write electronic configuration of oxygen as follows:

• Electronic Configuration of Oxygen is 1s² 2s² 2p⁴
• Here, the last shell is second shell which has 2 + 4 = 6 electrons
• Hence, the number of valence electrons in Oxygen is 6

Valence electrons are situated at the outermost highest energy level of an atom, making them the most available for creating molecular bonds. The number of valence electrons in one atom of any element is determined by its position in the periodic table. The valence electrons are the primary factors in chemical reactions that bond and react with other atoms or molecules. Hence, determining the elements’ reactivity, electronegativity, and the number of bonds they can form. In this article, we will look into what valence electrons are and how to find valence electron for atoms.