Characteristics of groups and periods in a periodic table

The elements of a group show similar chemical properties but there is a gradual variation in the physical properties of the elements in a group.

Atomic Size: From top to bottom in a group, the size of atom increases as a new shell to the atom.
Valence Electrons(V.E) : Number of valence electrons in a group are same
Valency: All elements in a group generally have the same valency

a. Valency of metal (IA to IIIA)= No. of V.E

b. Valency of non-metal (IVA to VIIIA)= 8 – No. of V.E

4.Metallic Character: increases from top to bottom in a group.

5. Electropositivity & reactivity of Metals:

Electropositivity is the tendency of an atom to lose its valence electrons and gain positive charge.
On moving down the group, atomic size increases.
So, the V.Es are far from the nucleus and the force of attraction between protons in the nucleus and valence electrons decreases.
Hence, the elements down the group can easily lose their V.E to form positive ions i.e. electropositivity and reactivity increases down the group. E.g. K>Na>Li

6. Electronegativity & reactivity of non-metals:

Electronegativity is the tendency of an atom to gain electrons and gain negative charge.
On moving down the group, atomic size increases.
So, the force of attraction between protons in the nucleus and electron being gained decreases.
Hence, the elements down the group have difficulty to gain electron to form negative ions i.e. electronegativity and reactivity decreases down the group. E.g. F<Cl<Br<I

Characteristics of Periods:

1. Atomic size:

The atomic size decreases from left to right in a period.
Along a period, with increase in atomic number, the number of protons and electrons increases.
So, there is increased force of attraction towards the nucleus. Hence, the atomic size shrinks and decreases.

2.Valence Electrons:

3. Valency:

Along a period from left to right, valency first increases from 1 upto 4 and then decreases upto zero.

2^nd Period	Li	Be	B	C	N	O	F	Ne
Valency	1	2	3	4	3	2	1	0

4. Electropositivity & reactivity of Metals:

From left to right in a period, the atomic size decreases due to the increase in nuclear force of attraction.
So, it is difficult to lose V.Es .Hence, electropositivity & reactivity of Metals decreases along the period.

5. Electronegativity & reactivity of non-metals:

From left to right in a period, the atomic size decreases due to the increase in nuclear force of attraction.
So, it is easy to gain electrons for a non-metal atom .Hence, electronegativity & reactivity of non-metals increases along the period.

Electronic Configuration: the distribution of electrons in different shells and subshells

Classification of Elements based on Electronic Configuration:

1. s-block elements:

The block of alkali metals (group IA or 1) i.e. Li to Fr and alkaline earth metals (group IIA or 2) i.e. Be to Ra which are present at the left hand side of the periodic table
These elements have the last electron in s-subshell

2. p- block elements:

the bock of metals, non-metals, metalloids and inert gases which are present in group IIIA to VIIIA(0) constitute p-block elements e.g. B, C, O, N, F, Ne etc.
present at the right hand side of the modern periodic table
these elements have the last electron in p-subshell

*Elements belonging to s-block and p-block are “normal” or “representative” elements.

3. d-block elements:

the block of transitional metals which is present in middle part of the modern periodic table
includes elements of group IB to VIIIB i.e. 3 to 12
these elements have last electron in d-subshell
their properties are midway between those of s-block & p-block, so they are called “Transitional elements”

4. f-block elements:

Memory Tips:

Group	IA (1)	IIA(2)	IIIA(13)	IVA(14)	VA(15)	VIA(16)	VIIA(17)	VIIIA(0)
Valency	1	2	3	4	3	2	1	0

Inert/Noble gases=Group VIIIA(0 or 18)

Author: Sulaksha Purna Shrestha

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