Chemistry

Atoms and Molecules

Gram Atomic Mass

The amount of a substance whose mass in grams is numerically equal to its atomic mass,is called gram atomic mass of that substance. In other words, the atomic mass of a substance expressed in gramsms called its gram atomic mass. To write the gram atomic mass of a substance, we write its atomic then replace the atomic mass unit 'u' by the word 'gram' or its symbol 'g'. For example .
Atomic mass of oxygen, O = 16 u
So, Gram atomic mass of oxygen, O = 16 grams (or 16 g)
The gram atomic mass of a substance represents the mass of 1 mole of atoms ( $6.022X10$ ²³ atoms) of that substance. So,the number of atoms present in 1 gram atom.e mass of any substance is

6.022X10

²³ atoms. The atomic mass of hydrogen (H) is 1 u, so the gram atomic mass of hydrogen (H) is 1 gram; the atomic mass of nitrogen (N) is 14 u, so the gram atomic mass o rutrogen (N) is 14 grams ; the atomic mass of oxygen (O) is 16 u, so the gram atomic mass of oxygen (O) is 16 grams, and the atomic mass of Sodium (Na) is 23 U,So the gram atomic mass of sodium element is 23 grams.
Before we go further, we will discuss a new term called 'molar mass .The molar mass of a substance is the mass of 1 mole of that substance.The unit of molar mass is grams per mole (which is written in short as g/mol).The molar mass can be of an element or of a molecular compound. The molar mass of an element is numerically equal to the atomic mass expressed in the units g/mol. And the molar mass of a molecular substance (or compound) is numerically equal to its molecular mass expressed in the units g/mol.
From the above discussion we conclude that another term which can be used in place of 'gram atomic mass' of an element is the 'molar mass' of element. The molar mass of an element is the mass of 1 mole of its atoms. The molar mass of an element has $6.022X10$ ²³ atoms of the element in it. As we have said above, the molar mass of an element is equal to the atomic mass of the element expressed in the units of g/mol. The atomic mass of hydrogen (H) is 1 u, so the molar mass of hydrogen element (H) is 1 g/mol; the atomic mass of nitrogen (N) is 14 u; so the molar mass of nitrogen element (N) is 14 g/mol; the atomic mass of oxygen (O) is 16 u, so the molar mass of oxygen element (O) is 16 g/mol; and the atomic mass of sodium (Na) is 23 u, so the molar mass of sodium element (Na) is 23 g/mol.
Please note that when we are dealing with the atoms of an element; we have to use its 'gram atomic mass' or 'molar mass of element'. But when we are dealing with the molecules of a substance, then we have to use its 'gram molecular mass' or 'molar mass of substance' (The substance containing molecules can be an element or a compound).

Notes

Atoms and Molecules - Notes

1. Drawbacks of Dalton’s Atomic Theory