Atoms are so incredibly tiny that expressing their mass in kilograms would give unimaginably small numbers. So scientists created a special unit called the AMU (Atomic Mass Unit) to conveniently express atomic masses.
1 AMU = 1.66054 × 10⁻²⁷ kg.
Defined as: 1/12 mass of Carbon-12 atom.
Proton mass ≈ 1 AMU.
Neutron mass ≈ 1 AMU.
Electron mass ≈ 0.00055 AMU (negligible).
1 AMU = 1.66054 × 10⁻²⁷ kg
Or equivalently: 1 AMU = 1.66054 × 10⁻²⁴ grams
In simpler terms, 1 AMU is approximately 1.66 × 10⁻²⁷ kg — an incredibly small number.
1 AMU is defined as 1/12th the mass of one atom of Carbon-12 (C-12).
Carbon-12 was chosen as the reference because it is the most abundant and stable carbon isotope, and its mass can be measured very precisely.
The mass of a proton is 1.673 × 10⁻²⁷ kg — an inconvenient number. In AMU, a proton's mass is simply 1.007 AMU ≈ 1 AMU, making calculations much cleaner. Similarly, Carbon-12 has an atomic mass of exactly 12 AMU.
1 AMU (Atomic Mass Unit) = 1.66054 × 10⁻²⁷ kg.
1 AMU is defined as exactly 1/12th the mass of one atom of Carbon-12.
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