Practice Mass Number in Chemistry

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

Quick Recap

The total count of protons and neutrons (collectively called nucleons) in an atom's nucleus, always a whole number, used to identify specific isotopes of an element.

How heavy the nucleus is — each proton and neutron contributes about 1 atomic mass unit.

Example 1

easy
An atom has 17 protons and 18 neutrons. What is its mass number and what element is it?

Example 2

medium
Why is the atomic mass of chlorine listed as 35.45 amu on the periodic table, rather than a whole number like 35 or 37?

Example 3

medium
An isotope has 26 protons and 30 neutrons. What is its mass number? Identify the element.

Example 4

easy
Find the mass number of an atom with 26 protons and 30 neutrons.

Example 5

easy
An atom has 17 protons and 18 neutrons. What is its mass number?
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