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Radioactivity

Isotopes, atomic number and mass number

  • 3 things to know
  • Paper 5

Overview

What atomic number and mass number count, finding neutrons by subtraction, reading nuclear symbols, what isotopes are, and why carbon-12 and carbon-14 react identically.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Key term

What does the atomic number of a nucleus tell you?

Key term

What does the mass number of a nucleus tell you?

Key term

How is the number of neutrons in a nucleus worked out from its mass number and atomic number?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What does the atomic number of a nucleus tell you?

    Model answer

    The atomic number is the number of protons in the nucleus.

  2. 2

    What does the mass number of a nucleus tell you?

    Model answer

    The mass number is the total number of protons and neutrons in the nucleus.

  3. 3

    How is the number of neutrons in a nucleus worked out from its mass number and atomic number?

    Model answer

    Subtract the atomic number from the mass number.

  4. 4

    In the symbol ¹³₆C, what do the numbers 13 and 6 represent?

    Model answer

    13 is the mass number and 6 is the atomic number.

  5. 5

    How many neutrons are there in a nucleus of ¹³₆C?

    Model answer

    There are 7 neutrons, because 13 − 6 = 7.

  6. 6

    What are isotopes?

    Model answer

    Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.

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