Question

How do you calculate the number of valence electrons in an atom?

Answer 1

Valence electron:

1. An electron that is part of an atom's outer shell and can take part in the formation of a chemical bond if the outer shell is not closed is known as a valence electron.
2. There are two ways to find valence electrons i.e. from the periodic table or from the electronic configuration.

Periodic table method:

1. Periodic table is a table listing the chemical elements in order of their atomic numbers
2. Groups and periods are two ways of categorizing elements in the periodic table. Periods are horizontal rows of the periodic table, while groups are vertical columns (down) the table.
3. For calculating the valence electron we need to look at the groups in the periodic table. For s-block and p-block elements, the valence electron is equal to the group number of the element.
4. Example: Sodium is the first group element so its, valence electron is equal to $1$, Oxygen belongs to the group $6\mathrm{A}$ or group $16$ it has six valence electrons.

Electronic configuration method:

1. Electronic configuration is also helpful in calculating the valence electron.
2. The number of valence electrons for any atom is equal to the number of electrons in its outermost shell.
3. Example: Electronic configuration of fluorine is$1{\mathrm{s}}^2,2{\mathrm{s}}^2,2{\mathrm{p}}^5$. It has five electrons in its $2\mathrm{p}$ orbital and two electrons in its $2\mathrm{s}$ orbital. Therefore, the valence electron of fluorine is equal to seven.

Therefore, we can determine valence electron by electronic configuration or from the periodic table.