Question

(a) What are the periods and groups in a periodic table? Give two characteristics of each.
(b) In terms of electronic configurations, explain the variation in the size of the atoms of the elements belonging to the same period and same group.
(c) Given alongside is a part of the periodic table. As we move vertically downward from Li to Fr:

Li	Be
Na
K
Rb
Cs
Fr	Ra

(i) What happens to the size of atoms?
(ii) What happens to their metallic character?
(d) Name two properties of elements whose magnitudes change when going from top to bottom in a group of the periodic table. In what manner do they change?
(e) Rewrite the following statement after correction, if necessary:
Groups have elements with consecutive atomic numbers.

Answer 1

(a) Periods are the horizontal rows of elements and Groups, the vertical columns of elements in the periodic table.

Characteristics of groups:
1. Elements of the same group have the same number of valence electrons.
2. Elements of the same group exhibit similar chemical properties as they have the same valency.

Characteristics of periods:
1. Elements of the same period have the same number of shells.
2. The valency of elements in the same period changes, and therefore, the elements in a period exhibit different chemical properties.

(b) The size of the atom increases on moving from top to bottom in the same group because at every step, new shells of electrons are added.
In a period, the size of the atom decreases on moving from left to right. This is because the atomic number of the elements increases on moving from left to right. Thereby, the number of electrons and protons also increases. Due to the increment in the number of protons, the nuclear charge also increases and the electrons get held more tightly to the nucleus.

(c) When we move vertically down from Li to Fr:
(i) The size of the atom increases.
(ii) The metallic character of the elements increases.

(d) On moving from top to bottom in a group , the size of the atoms and the metallic character of the elements increases.

(e) Periods have elements with consecutive atomic numbers.