Name the elements in correct order of their increasing atomic numbers present in the first, second and third short periods of the periodic table. State each elements electronic configuration.

Elements of the first, second and third periods in increasing order of their atomic number are mentioned below (the atomic number of each element is mentioned in brackets):

• First period – H (1), He (2)
• Second period – Li (3), Be (4), B (5), C (6), N (7), O (8), F (9), Ne (10)
• Third period – Na (11), Mg (12), Al (13), Si (14), P (15), S (16), Cl (17), Ar (18)

The electronic configuration of the above-mentioned elements is as follows —

H — 1

He — 2

Li — 2, 1

Be — 2, 2

B — 2, 3

C — 2, 4

N — 2, 5

O — 2, 6

F — 2, 7

Ne — 2, 8

Na — 2, 8, 1

Mg — 2, 8, 2

Al — 2, 8, 3

Si — 2, 8, 4

P — 2. 8, 5

S — 2, 8, 6

Cl — 2, 8, 7

Ar — 2, 8, 8