Unified atomic mass unit (u)

Definition

The unified atomic mass unit (u) is a standard unit of mass that quantifies the mass of atoms and molecules. It is defined as one twelfth the mass of a carbon-12 atom.

5 Must Know Facts For Your Next Test

1. The unified atomic mass unit is also known as the dalton (Da).
2. 1 u is approximately equal to $1.66053906660 \times 10^{-27}$ kilograms.
3. The unified atomic mass unit provides a convenient way to express atomic and molecular masses without using extremely small numbers.
4. It simplifies calculations in chemistry, especially when dealing with molar masses and stoichiometry.
5. The definition of u is based on the carbon-12 isotope, which has exactly 12 u.

Review Questions

• What is the definition of a unified atomic mass unit?
• How does the unified atomic mass unit simplify chemical calculations?
• Why is carbon-12 used as the reference for defining the unified atomic mass unit?

Related terms

Molar Mass: The mass of one mole of a substance, usually expressed in grams per mole (g/mol), which can be calculated using the unified atomic mass units of its constituent atoms.

Isotope: Variants of a particular chemical element that differ in neutron number, and consequently in nucleon number but not in chemical properties.

Avogadro's Number: $6.02214076 \times 10^{23}$, which is the number of atoms or molecules in one mole of a substance.