Mass Number

The mass number of an atom is the total number of protons and neutrons in the nucleus of the atom. It is represented by the symbol A. The mass number is an important property of an atom, as it helps determine the atom's stability and its identity.

How to Calculate Mass Number

To calculate the mass number of an atom, you simply add the number of protons and neutrons together. This is because protons and neutrons have approximately the same mass, so the mass number is essentially a count of the total number of nucleons in the nucleus.

Significance of Mass Number

The mass number is used to differentiate between different isotopes of an element. Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. This means they have different mass numbers. For example, carbon-12 and carbon-14 are both isotopes of carbon, with mass numbers 12 and 14 respectively.

Study Guide

When studying mass number, it is important to remember the following key points:

• The mass number (A) is the total number of protons and neutrons in the nucleus of an atom.
• Isotopes of an element have the same number of protons but different mass numbers due to differing numbers of neutrons.
• The mass number is used to determine the atomic mass of an element.
• The mass number is not the same as the atomic number, which is the number of protons in an atom's nucleus.

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