Question

Using the periodic table, how can you tell how many valence electrons an element has?

Answer 1

Hint: The number of valence electrons can easily be calculated if one knows the electronic configuration and filling of orbitals in each group of the periodic table.

Complete step by step answer:
We know that the modern periodic table arranges the elements based on their respective atomic numbers and thus the whole periodic table is divided into several groups and periods. Starting from the left is the first group and at the very right is the eighteenth group which is the noble gas group. In each group, there is a specific number of electrons in the valence shell which is uniform throughout the entire group.
The first two groups of the periodic table are the groups concerned with the filling of the s orbital. Thus, the elements in group 1 will have only one electron in its valence shell in s orbital Similarly, the second group of the periodic table will have an outermost s orbital filled with two electrons of different spins. The groups of boron family, carbon family, nitrogen family, oxygen family and halogens are the groups concerned with the filling of the p orbital. So, members of the boron family will have three valence electrons; two in s orbital and one in the p orbital.
Similarly, members of the carbon family will have four valence electrons; two in s orbital and two in the p orbital.
Members of the nitrogen family will have five valence electrons; two in s orbital and three in the p orbital.
Members of the oxygen family will have six valence electrons; two in s orbital and four in the p orbital.
Members of the halogen family will have seven valence electrons; two in s orbital and five in the p orbital.
Members of the noble gas group will have its octet complete with two electrons in the s orbital and six electrons in the p orbital.

Note: Each new element of the periodic table adds a valence electron. A new period of the Periodic table starts with s electron and ends with 6p electrons. The (n - 1) d electrons are added before the n P electrons and the (n - 1) f electrons are added before n d electrons.