Atomic Mass Calculator

Calculate atomic mass using protons, neutrons, and natural isotope abundance

Calculate Atomic Mass

Number of Protons Element: Carbon

Number of Neutrons Mass Number: 12

Atomic Mass Formula

Atomic Mass ≈ Mass Number = Protons + Neutrons

*This gives the mass of a specific isotope

Isotope Mass (u) Abundance (%)

Weighted Average Formula

Atomic Mass = Σ(Mass_i × Abundance_i) / 100

*This gives the natural atomic mass

Common Elements

Calculation Results

Element: Carbon

Atomic Number: 6

Mass Number: 12

                        Atomic Mass:
                        12.01 u
                    

Calculation Breakdown

For a single isotope: Atomic Mass = Protons + Neutrons

6 protons + 6 neutrons = 12 atomic mass units

Atomic Structure

Nucleus: ~99.9% of mass

Mass Contribution:

Protons: 6.042 u

Neutrons: 6.054 u

Electrons: 0.003 u (negligible)

What is Atomic Mass?

Atomic mass is the weighted average mass of all naturally occurring isotopes of an element, measured in atomic mass units (u).

⚖️ Measured in atomic mass units (u)

📊 Weighted average of isotopes

🔢 1 u = 1/12 mass of Carbon-12

Atomic Mass Unit (u)

One atomic mass unit is defined as exactly 1/12 the mass of a carbon-12 atom.

1 u = 1.660539 × 10^-27 kg

1 u = 931.494 MeV/c²

This standardized unit allows precise measurement of atomic masses.

Why Atoms Need Neutrons

Nuclear Stability

Neutrons provide the strong nuclear force that holds the nucleus together against proton repulsion.

Isotope Formation

Different numbers of neutrons create isotopes with varying stability and properties.

Mass Contribution

Neutrons contribute significantly to atomic mass while remaining electrically neutral.

Common Atomic Mass Examples

Hydrogen (H)

1.008 u

Protium (1H): 1.0078 u (99.98%)

Deuterium (2H): 2.0141 u (0.02%)

Carbon (C)

12.011 u

Carbon-12: 12.000 u (98.93%)

Carbon-13: 13.003 u (1.07%)

Oxygen (O)

15.999 u

Oxygen-16: 15.995 u (99.76%)

Oxygen-17: 16.999 u (0.04%)

Oxygen-18: 17.999 u (0.20%)

Chlorine (Cl)

35.45 u

Chlorine-35: 34.969 u (75.77%)

Chlorine-37: 36.966 u (24.23%)

Atomic Mass Formulas

Single Isotope Mass

Mass ≈ A = Z + N

Where:
A = Mass number
Z = Atomic number (protons)
N = Neutron number

Weighted Average Mass

m = Σ(mᵢ × fᵢ)

Where:
m = Atomic mass
mᵢ = Mass of isotope i
fᵢ = Fractional abundance of isotope i

Mass Defect

Δm = Z·mₚ + N·mₙ – mₐ

Where:
mₚ = Proton mass (1.00728 u)
mₙ = Neutron mass (1.00867 u)
mₐ = Actual atomic mass