The elements A and B have electronic configurations 2, 8, 18, 2, and 2, 6 respectively.

1. To which period do A and B belong in the modern periodic table.
2. To which group do A and B belong in the modern periodic table.

Modern periodic table:

• The modern periodic table is an arrangement of all the elements known in accordance with their increasing atomic number and recurring chemical properties.
• It is a tabular display of 118 chemical elements which consists of horizontal rows called periods and vertical columns are called groups.
• All elements in a group have the same number of valance electrons, and in period elements have the same number of electron shells.
• There are seven periods and eighteen groups in the modern periodic table.

Electronic configuration:

• Electronic configuration, also called electronic structure, is the arrangement of electrons in energy levels around an atomic nucleus.
• The electron configuration of an element describes how electrons are distributed in its atomic orbitals.
• It can be written in K, L, M, and N format. Where the K, L, M, and N shells represent the energy shells.
• The total number of an electron in the shell is given by the formula 2N², where N is the shell number.
• For the K shell maximum number of electrons that can be acquired is 2, for the L shell maximum number of electrons that can be acquired is 8.

1) Element A belongs to the fourth period because it has four shells (2,8,18,2).

The element B belongs to the second period because it has two shells (2,6).

2.) Element A belongs to the second group because it has two valance electrons.

The element B belongs to the sixteenth group because it has six valance electrons.