Explain the significance of the formula H 2 O.

The significance of formula 'H 2 O' is: (i) Water (ii) The elements present are Hydrogen and oxygen (iii) One molecule of water (iv) That one molecule of water contains 2 atom of hydrogen and 1 atom of oxygen. (v) Its atomicity is 3, that is, it is a triatomic molecule (vi) One mole of water (vii) 18 g of H 2 O (that is, molecular mass expressed in grams) (viii) 6 . 022 X 10 23 molecules of water.

What is the difference between 2H and H 2 ?

2H represents two atoms of hydrogen. These atoms cannot exist in free state whereas H 2 represents a molecule of hydrogen that can exist in free state. Atoms exist in the combined state with other atoms of the same element or atoms of different element. A molecule is the smallest particle of an element or a compound which can exist freely under ordinary conditions and shows all the properties of that substance.