Atomic mass and formula mass are fundamental concepts used to measure the mass of atoms and compounds.
1. Atomic Mass:
- It is the average mass of an atom of an element
- Measured in atomic mass units (u)
- Takes into account the relative abundance of isotopes
Example:
Atomic mass of carbon = 12 u
2. Formula Mass:
- It is the sum of atomic masses of all atoms in a chemical formula
- Used for ionic compounds or substances without discrete molecules
Example:
For NaCl:
Na = 23 u, Cl = 35.5 u
Formula mass = 23 + 35.5 = 58.5 u
Key Difference:
- Atomic mass → mass of a single atom
- Formula mass → mass of a compound (sum of atoms in formula)
Key Takeaway:
Atomic mass refers to individual atoms, while formula mass refers to the total mass of all atoms in a compound’s formula.