The Periodic Table Basic Features

The modern periodic table is divided into eight vertical columns known as groups and seven horizontal rows known as periods.

Groups:

Groups 1 to 8(0) which constitute the chemical families are named as follows

Elements in the same group have the same number of valence electrons in their respective atoms.  Example, Group 1 Elements ₃L_i → 2, 1, ₁₁Na → 2, 8, 1, ₁₉K → 2, 8, 8, 1.  They all have one electron in their outermost shell.  The group an element belongs to corresponds to the number of electrons in the outermost shell (except for group 0 elements)

The elements which occur between Alkaline earth metals and the Boron family are regarded as transition elements. The elements in Groups 3 – 7 are known as representative elements.

Periods:

Elements are arranged in horizontal rows according to periods. The periods are numbered from 1 to 7. Elements in the same period have the same number of electron shells.

e.g. ₃Li → 2, 1, ₄Be → 2, 2, ₅B → 2, 3, ₆C → 2, 4, ₇N → 2, 5. ₈O → 2, 6, ₉F → 2, 7, ₁₀Ne → 2, 8.

The number of valence electrons of the elements in the same period increases progressively by one across the period from left to right.

Period 1 contains only two elements; Hydrogen and Helium. They have only one electron shell; ₁H → 1, ₂He → 2;

Period I – their elements occupy the K shell.

Period II – their elements occupy K, L shell

Period III – their elements occupy K, L, M shell

Period IV – their elements occupy K, L, M, N shell.

The elements in periods 6 and 7 are known as lanthanide and actinide series. They are also known as inner transition elements.