Metals And Non Metals

Metalloids
Metalloids are the elements which show both metallic and non-metallic properties. 
Ex:Boron, Silicon, Germanium,Arsenic,Antimony, Selenium ,Tellurium
There are 7 metalloids in nature


NOBLE GASES:
These elements are found in air in the form of gas in very small amounts.Hence they are called as Rare gases. They are monoatomic in nature.These elements do not react chemically with other elements, so these are also called as Noble gases.
    Ex: Helium,Neon,Argon ,Krypton, Xenon and Radon.
NOTE: 
    * Helium is second  lightest element after hydrogen. 
    * Radon is radioactive element.

ATOMICITY:
    The number of atoms that constitute a moleculeof an element is called  Atomicity.
    i) Monoatomic elements:The elements in which each molecule contains only one atom.
    Ex:Copper(Cu), Silver (Ag)....
    ii)Diatomic elements:The elements in which each molecule contains two atoms.
    Ex: Hydrogen (H₂),Oxygen (O₂).....
    iii)Polyatomic elements:The elements in which each molecule contains more than  two atoms.
    Ex: Ozone(O₃), Phosphorus(P₄),Sulphur (S₈), Boron (B₁₂).