How to Find the Mass Number of Lithium?

The mass number of lithium is found by adding the number of protons and neutrons in the nucleus of a lithium atom.

Understanding Mass Number

The mass number (A) is a fundamental property of an atom that represents the total number of nucleons (protons and neutrons) present in the nucleus. It's crucial for identifying isotopes and understanding nuclear reactions.

Calculating Lithium's Mass Number

Here's how to determine the mass number of lithium:

1. Identify the Number of Protons: Lithium always has 3 protons. This is what defines it as lithium (atomic number = 3).
2. Identify the Number of Neutrons: Lithium can have different numbers of neutrons, leading to different isotopes. The most common isotope of lithium has 4 neutrons.
3. Add Protons and Neutrons: Mass Number (A) = Number of Protons + Number of Neutrons. For the most common isotope: A = 3 + 4 = 7.

Therefore, the most common isotope of lithium has a mass number of 7. Other isotopes of lithium exist with different numbers of neutrons, and therefore, different mass numbers. For example, Lithium-6 has 3 protons and 3 neutrons, giving it a mass number of 6.

Example

Let's consider the most common isotope of Lithium, Lithium-7 (⁷Li):

Particle	Number
Protons	3
Neutrons	4
Electrons	3

Mass Number (A) = 3 + 4 = 7

Therefore, the mass number of Lithium-7 is 7.