Edexcel IGCSE Chemistry

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1.6.1 Formation of Ions

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Formation of Ions

  • An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons
  • This loss or gain of electrons takes place to obtain a full outer shell of electrons
  • The electronic structure of ions of elements in groups 1, 2, 3, 5, 6 and 7 will be the same as that of a noble gas - such as helium, neon, and argon
  • Negative ions are called anions and form when atoms gain electrons, meaning they have more electrons than protons
  • Positive ions are called cations and form when atoms lose electrons, meaning they have more protons than electrons
  • All metals lose electrons to other atoms to become positively charged ions
  • All non-metals gain electrons from other atoms to become negatively charged ions

1-6-1-formation-of-ions-1

Diagram showing the formation of the sodium ion

1-6-1-formation-of-ions-2

Diagram showing the formation of the chloride ion

Exam Tip

The number of electrons that an atom gains or loses is the same as the charge.

For example, if a magnesium atom loses 2 electrons, then the charge will be 2+, if a bromine atom gains 1 electron then the charge will be 1-.

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