Isotope Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Isotope.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

Atoms of the same element that have the same number of protons but different numbers of neutrons, giving them different mass numbers.

Same element, slightly different weight. Chemically identical, but different mass.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Isotopes have the same atomic number but different mass numbers.

Common stuck point: Isotopes of an element behave identically in chemical reactions.

Worked Examples

Example 1

easy
Carbon has three naturally occurring isotopes: {}^{12}\text{C}, {}^{13}\text{C}, and {}^{14}\text{C}. How many protons and neutrons does each have?

Solution

  1. 1
    Isotopes of the same element have the same atomic number but different mass numbers. All carbon isotopes have Z = 6, so each has 6 protons.
  2. 2
    Use the formula N = A - Z to find neutrons for each isotope: {}^{12}\text{C}: 12 - 6 = 6 neutrons; {}^{13}\text{C}: 13 - 6 = 7 neutrons; {}^{14}\text{C}: 14 - 6 = 8 neutrons.
  3. 3
    Summary: {}^{12}\text{C} (6n), {}^{13}\text{C} (7n), {}^{14}\text{C} (8n) — same element, different neutron counts.

Answer

{}^{12}\text{C: 6p, 6n}\quad {}^{13}\text{C: 6p, 7n}\quad {}^{14}\text{C: 6p, 8n}
Isotopes are atoms of the same element (same number of protons) that differ in the number of neutrons. They have identical chemical properties but different masses.

Example 2

medium
Boron has two stable isotopes: {}^{10}\text{B} (19.9%) and {}^{11}\text{B} (80.1%). Calculate the average atomic mass of boron.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

hard
Copper has two stable isotopes: {}^{63}\text{Cu} and {}^{65}\text{Cu}. The average atomic mass of copper is 63.55 amu. Calculate the percent abundance of each isotope.

Example 2

medium
Chlorine-35 and chlorine-37 are both chlorine. What is different about them, and what stays the same?
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Background Knowledge

These ideas may be useful before you work through the harder examples.

neutronmass number