Classification of elements in the periodic table according to the sub-shell filled by the last electron.

Classification of elements in the periodic table according to last sub-shell:

Elements in the periodic table can be classified by the sub-shell that is filled by the last electrons.

There are four blocks of elements in the periodic table:

1)  s – block elements

2)  d – block elements

3)  p – block elements

4) f – block elements

1)  s – block elements :

The elements which have their last electron is being filled on “ s ”  sub – shell.

The Group 1 and Group 2 elements in the periodic table are s – block elements.

For example :

Li ( z = 3) = 1s² 2s¹

Be ( z = 4) = 1s²  2s²

Na ( z =  11) = 1s² 2s² 2p⁶ 3s¹                                     Or            [Ne] 3s¹

Mg ( z =  12) = 1s² 2s² 2p⁶ 3s²                                    Or             [Ne] 3s²

2)  d – block elements :

The elements which have their last electron is being filled on “ d ”  sub – shell.

The elements between Group 2 and Group 3 that is transition metals in the periodic table are d – block elements.

For example :

Sc  ( z =  21) = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d¹            Or         [Ar] 4s² 3d¹

Ti ( z =  22) = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d²               Or        [Ar] 4s² 3d²

V ( z =  23) = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d³                Or        [Ar] 4s² 3d³

Ni ( z =  28) = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d⁸                 Or        [Ar] 4s² 3d⁸  

3)  p – block elements :

The elements which have their last electron is being filled on “ p ”  sub – shell.

The Group 3 to Group 8 elements in the periodic table are s – block elements.

For example :

Al ( z =  13) = 1s² 2s²  2p⁶  3s² 3p¹                           Or             [Ne] 3s² 3p1

Si ( z =  14) = 1s²  2s² 2p⁶ 3s² 3p²                             Or             [Ne] 3s² 3p3

P ( z =  15) = 1s² 2s² 2p⁶ 3s² 3p³                                Or             [Ne] 3s² 3p3

S ( z =  16) = 1s² 2s² 2p⁶ 3s² 3p⁴                                Or             [Ne] 3s² 3p4

4) f – block elements :

The elements which have their last electron is being filled on “ f ”  sub – shell.

We don’t have f – block elements in our AS level Chemistry specification.

Diagram:

Classification of elements in the periodic table according to last sub-shell.

The electron configuration of ions:

Li ( z = 3) = 1s² 2s¹

Li⁺ ( z = 3) = 1s² 2s⁰

Na ( z =  11) = 1s² 2s² 2p⁶ 3s¹                                     Or            [Ne] 3s¹   

Na⁺ ( z =  11) = 1s² 2s² 2p⁶ 3s⁰                                     Or            [Ne] 3s⁰

                                                                                                                                                             

Mg ( z =  12) = 1s² 2s² 2p⁶ 3s²                                    Or             [Ne] 3s²

Mg²⁺ ( z =  12) = 1s² 2s² 2p⁶ 3s⁰                                   Or             [Ne] 3s⁰

Al ( z =  13) = 1s² 2s²  2p⁶  3s² 3p¹                           Or             [Ne] 3s² 3p¹

Al³⁺ ( z =  13) = 1s² 2s²  2p⁶  3s² 3p¹                           Or             [Ne] 3s⁰ 3p⁰

N  ( z = 7) = 1s² 2s² 2p³

N³⁺  ( z = 7) = 1s² 2s² 2p⁰

O ( z =  8) = 1s² 2s² 2p⁴

O^2- ( z =  8) = 1s² 2s² 2p⁶

F ( z =  9) = 1s² 2s² 2p⁵

F^- ( z =  9) = 1s² 2s² 2p⁶