Atoms & Ions (Oxford AQA IGCSE Physics)

Neutral Atoms

• Although atoms contain particles of different charge, the total charge within an atom is zero

  • This is because the number of electrons is equal to the number of protons

Atomic structure of a lithium atom

• The following table sets out the calculation of the total charge in the lithium atom:

Total Charge Calculation Table

Ions

• If an atom gains or loses electrons, an ion is formed

• An ion is an electrically charged atom

• Positive ions are therefore formed when atoms lose negative electrons

  • There will be more positive protons than negative electrons

• Negative ions are therefore formed when atoms gain negative electrons

  • There will be more negative electrons than positive protons

Atomic structure of an atom, a negative ion and a positive ion

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

• For example, if an atom loses 2 electrons, then the charge on the resulting ion will be +2

• If an atom gains 1 electron, then the charge on the resulting ion will be -1