An example of a mass number is 12, which is the mass number of a carbon atom.
Understanding Mass Number
The mass number of an atom is the total count of protons and neutrons in its nucleus. It's a whole number that helps to identify a specific isotope of an element. Here's a breakdown:
- Protons: These are positively charged particles found in the nucleus of an atom. The number of protons determines the element.
- Neutrons: These are neutral particles, also found in the nucleus. They contribute to the mass of the atom but do not affect its elemental identity.
- Mass Number Calculation: The mass number is calculated by simply adding the number of protons and neutrons in an atom's nucleus.
Example: Carbon
According to the provided reference, an atom of carbon has 6 protons and 6 neutrons.
- Protons = 6
- Neutrons = 6
Therefore:
- Mass number = 6 + 6 = 12.
Isotopes and Mass Numbers
It's important to note that while the number of protons in an atom remains constant for a given element, the number of neutrons can vary. This variation leads to isotopes, which are atoms of the same element with different mass numbers. For example, a carbon atom can have 6 protons and 7 neutrons, giving it a mass number of 13 and making it a carbon-13 isotope.
- Carbon-12 (12C): 6 protons and 6 neutrons; Mass Number is 12.
- Carbon-13 (13C): 6 protons and 7 neutrons; Mass Number is 13.
- Carbon-14 (14C): 6 protons and 8 neutrons; Mass Number is 14.
Summary Table
| Isotope | Protons | Neutrons | Mass Number |
|---|---|---|---|
| Carbon-12 | 6 | 6 | 12 |
| Carbon-13 | 6 | 7 | 13 |
| Carbon-14 | 6 | 8 | 14 |
Thus, the mass number is a key indicator of the specific isotope of an element.
