THE PERIODIC TABLE
Groups and Periods
Groups: There are eight main groups in the periodic
table; I, II, III, IV, V, VII, VII and O (or VIII)
Elements in the same group have the same number of
valence electrons in their respective atoms. For
instance Li (2s1), Na (3s1) and K (4s1) have one valence
electrons in the highest occupied orbital.
Certain groups of elements have family names
Group I elements are called alkali metals
Group II elements are alkaline-earth metals
Group VII elements are known as halogens
Group O are called noble, inert or rare gases.
Periods: Atoms of elements in the same period have
the same number of shells of electrons.
Periodic Atomic Property
Periodicity: This is the recurrence of similar
phenomena at regular intervals.
The following properties of atoms exhibit periodicity
I. Atomic radius
II. Electronegativity
III. Ionization energy
IV. Electron affinity
I. Atomic radius: The radius of an atom is the
distance between the centre of the nucleus and the
outermost electronic shell. Atomic radius increases
steadily down the group due to the increase in the
number of electronic shells, while across the period
atomic radius decreases due to the steady increase in
the number of protons in the nucleus