Characteristics of periods and groups

CHARACTERISTICS OF PERIODS

Valence Electrons (or Outermost Electrons)

• On moving from left to right in a period, the number of valence electrons in elements increases from 1 to 8.

Valency

• On moving from left to right in each short period, the valency of elements increases from 1 to 4. Then decreases to 0 (zero).

Size of Atoms (or Atomic size)

• On moving from left to right in a period, the size of atoms(atomic size) decreases.

Metallic Character

• On moving from left to right in a period, the metallic character of elements decreases, whereas the non-metallic character increases.

Chemical Reactivity

• On moving from left to right in a period, the chemical reactivity of elements first decreases and then increases.

CHARACTERISTICS OF GROUPS:

Valence Electrons (or Outermost Electrons)

• All the elements of a group of the periodic table have the same number of valence electrons.
• For example, group I elements: Li, Na, K etc., all have a valency of . Elements of group 17: Cl, Br, I etc., all have valency of .

Valency

• All the elements in a group have the same valency.

Size of Atoms (or Atomic size)

• While going down in a group of the periodic table, the size of atoms increases (or atomic size increases). This is due to the addition of new electronic shells.

Metallic Character

• While going down in a group of the periodic table, the metallic character of elements increases.
• For example, groups 14 and 15 begin with carbon and nitrogen which are non-metals. These groups and end with lead and bismuth respectively which are metals.

Chemical Reactivity

• All the elements of a group show similar chemical properties.