Mass number examples include the total number of protons and neutrons found within the nucleus of an atom, essentially providing an indication of an atom's mass. Here are some examples:
Understanding Mass Number
The mass number is not found on the periodic table, as that contains the atomic number. The mass number is calculated by adding the number of protons and neutrons in the nucleus of an atom.
- Protons: Positively charged particles found in the nucleus.
- Neutrons: Neutral particles found in the nucleus.
Mass Number Examples
Here are examples of different elements and their mass numbers:
| Element | Number of Protons | Number of Neutrons | Mass Number |
|---|---|---|---|
| Carbon (C) | 6 | 6 | 12 |
| Carbon (C) | 6 | 8 | 14 |
| Oxygen (O) | 8 | 8 | 16 |
| Sodium (Na) | 11 | 12 | 23 |
| Uranium (U) | 92 | 146 | 238 |
Isotopes and Mass Number Variation
An important note: Elements can have different isotopes. Isotopes are atoms of the same element that have different numbers of neutrons. This means that they can have different mass numbers.
For example, Atoms of a carbon consist of 6 protons and 6 neutrons. Therefore, the mass number of Carbon is 12. However, carbon can also exist with 6 protons and 8 neutrons, resulting in a mass number of 14. The number of neutrons may vary in an element. However, the total number of protons is the same in all atoms of an element.
Key Takeaways
- The mass number is the sum of protons and neutrons.
- It is crucial for identifying different isotopes of an element.
- The mass number varies based on the neutron count of the atom.
