The physical and chemical properties of elements show a regular variation in the oeriods and groups of the periodic table.
The properties of an element are a periodic function of their atomic number according to the modern periodic table, are related to the electronic configuration of the elements.
There is a common trend in properties as one moves across a period from left to right or down the group.
This trend in properties is known as periodic properties, the most significant among which are atomic size, metallic character, non-metallic character, ionization potential, electron affinity, and electronegativity.
VALENCY:
On moving from left to right in each short period, the valency of elements increases from 1 to 4 and then decreases to zero.
Elements in the same period have different valencies.
Valency of an element is determined by the number of valence electrons present in the atom of the element.
The number of electrons lost or gained by one atom of an element to achieve the nearest inert gas configuration, gives the valency of the element.
ATOMIC SIZE TRENDS:
Atomic radius is the distance between the center of the nucleus and the outermost shell of an atom.
The atomic size increases in a group due to the addition of shells as one move from one period to another.
The atomic size decreases across a period as the number of shells remain the same but nuclear charge increases.
So, electrons are pulled from the outermost shell towards the nucleus and their size reduces.
METALLIC CHARACTER TRENDS:
Metals are the elements which lose electrons to form cations.
Metallic character increases as we move down the group.
This is because the atomic size increases so that electrons are lost easily.
The atomic size decreases across a period as we move from left to right because there is an increase in nuclear charge.
So it is difficult for an atom to lose electrons.
NON-METALLIC CHARACTER TRENDS:
Non-metals are the elements which have a tendency to gain electrons.
The non-metallic character increases as one move across a period.
This is due to an increase in the nuclear charge and decrease in the atomic size.
But as we move down the group the non-metallic character decreases due to increase in the atomic size.
CHEMICAL REACTIVITY:
On moving from left to right in a period, the chemical reactivity of elements first decreases and then increases.
All the elements of a group show similar chemical properties.
The chemical reactivity of metals increases on going down in a group of the periodic table.
The chemical reactivity of non-metals decreases on going down in a group of the periodic table.
NATURE OF OXIDES:
On moving from left to right in a period, the basic nature of oxides decreases and the acidic nature of oxides increases.
Ongoing down in a group of the periodic table, there is no change in the nature of oxides of element.
