1. Protons: Each proton in the nucleus contributes a mass of approximately 1 atomic mass unit (amu). The number of protons is often referred to as the atomic number and is unique for each element.
2. Neutrons: Each neutron in the nucleus also contributes a mass of approximately 1 amu. Neutrons typically have a similar number to protons in most stable atoms, but this can vary.
3. Mass Number Calculation: The mass number of an atom is the sum of the number of protons (atomic number) and the number of neutrons in the nucleus.
For example, let's determine the mass number of a carbon atom:
- Carbon has an atomic number of 6, which means it has 6 protons.
- The number of neutrons in a stable carbon atom is also 6.
Therefore, the mass number of a carbon atom is:
Mass Number = Number of Protons + Number of Neutrons
Mass Number (Carbon) = 6 (protons) + 6 (neutrons) = 12
So, the mass number of a carbon atom is 12.
This approach applies to calculating the mass number of any element. The mass number provides essential information about the composition of an atom.
