Isotopes (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award)): Revision Note

Defining isotopes

• Isotopes are different atoms of the same element that contain the same number of protons but a different number of neutrons

• The symbol for an isotope is the chemical symbol (or word) followed by a dash and then the mass number

• So C-14 ( or carbon-14) is the isotope of carbon which contains 6 protons, 6 electrons and 14 - 6 = 8 neutrons

  • It can also be written as ¹⁴C or

Table to show the structures of isotopes of hydrogen

Isotope	Atomic Structure	Symbol
Hydrogen - 1
Hydrogen - 2
Hydrogen - 3

Why isotopes share properties

Extended tier only 

• Isotopes display the same chemical characteristics

• This is because they have the same number of electrons in their outer shells, and this is what determines their chemistry

• The difference between isotopes is the neutrons which are neutral particles within the nucleus and add mass only

• The difference in mass affects the physical properties, such as density, boiling point and melting point

• Isotopes are identical in appearance, so a sample of C-14 would look no different from C-12