Atom Chemistry Example 2

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Example 2

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A carbon atom has 6 protons, 6 neutrons, and 6 electrons. Calculate the approximate mass of this atom in atomic mass units (amu), given that protons and neutrons each have a mass of approximately 11 amu and electrons have negligible mass.

Solution

  1. 1
    Mass contribution from protons: 6×1 amu=6 amu6 \times 1\,\text{amu} = 6\,\text{amu}.
  2. 2
    Mass contribution from neutrons: 6×1 amu=6 amu6 \times 1\,\text{amu} = 6\,\text{amu}.
  3. 3
    Electron mass is negligible (≈0.0005 amu\approx 0.0005\,\text{amu} each), so total ≈6+6=12 amu\approx 6 + 6 = 12\,\text{amu}.

Answer

Mass≈12 amu\text{Mass} \approx 12\,\text{amu}
Nearly all the mass of an atom resides in its nucleus. Electrons contribute less than 0.05% of the total mass, which is why we often ignore their mass in calculations.

About Atom

The smallest unit of an element that retains the chemical properties of that element.

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