CBSE Class 9 Answered

Atomic mass: The mass of an atom or a molecule is referred to as the atomic mass.

Example:  Atomic mass of oxygen atom is 16 u

Atomic weight: The average mass of atoms of an element, calculated using the relative abundance of isotopes in a naturally-occurring element. It is the weighted average of the masses of naturally-occurring isotopes.

Example: Atomic mass of oxygen atom is 16 g

Mass number: Mass number is a count of the total number of protons and neutrons in an atom's nucleus.

Example: Mass number of oxygen atom is 16.

Molar mass: The molar mass, also known as molecular weight, is the sum of the total mass in grams of all the atoms that make up a molecule per mole. Its unit is in grams per mole.

Example: Molar mass of oxygen molecule is 32 u as oxygen is a diatomic molecule.

Atomic mass unit: Atomic mass unit or amu, in chemistry and physics, unit defined as exactly 1/12 the mass of an atom of carbon-12, the isotope of carbon with six protons and six neutrons in its nucleus. One amu is equal to approximately 1.66 × 10¯²⁴grams.