Question

define periodicity of properties. Explain taking metallic character of elements as an example

Answer 1

Periodicity of an element is defined as the trend in properties of an element arranged in the periodic table with increasing atomic number or mass.
The periodic properties are
1. Atomic size
2. Ionisation energy
3. Electron affinity
4. Electronegativity
5. Metallic character.

Metallic character increases down the group, as the metals are more electropositive (ready to give its electron) and decreases across the period as the electropositivity decreases.
For ex., When we move along the group, alkalimetal like Li,Na,K,Rb,Cs. The metallic character increases from Li to Cs. Thus Cs is more metallic and Li is less metallic. Similarly when we move across the period Li to Ne, the metallic character decreases.Thus Li is more metallic and Ne is less metallic in character . i.e., Ne is a non metal.