What is the mass number of lithium?

Lithium, which has atomic number 3, has 3 protons in its nucleus. If its atomic number is 3 (which is the number of protons in its nucleus) and its mass number is 7, we can find the number of neutrons by subtracting the atomic number from the mass number. read more

The two stable isotopes of Lithium are Lithium-6 with three protons and three neutrons having mass number 6, and Lithium-7 with three protons and 4 neutrons having mass number 7. Since it is the number of protons that identifies an element, all isotopes of Lithium have 3 protons. read more