Ions

Normally, atoms are neutral. They have the same number of protons in the nucleus as they have electrons orbiting in the energy levels around the nucleus.

Atoms can, however, lose or gain electrons due to collisions or other interactions. When they do, they form charged particles called ions:

  • if the atom loses one or more electrons, it becomes a positively-charged ion
  • if the atom gains one or more electrons, it becomes a negatively-charged ion
Helium ion, two neutrons, two protons and two electrons.

A helium atom has two electrons in an energy level outside the nucleus. The atom is neutral as it has two positive protons and two negative electrons.

A helium atom that has lost or gained an electron is an ion.

The ion has two positive protons but one electron so it is a positive ion:

Helium ion, two neutrons, two protons and one electron.

The ion has two positive protons but three electrons so it is a negative ion:

Helium ion, two neutrons, two protons and three electrons.
curriculum-key-fact
Remember: Change the number of neutrons in an atom and it becomes an isotope, change the number of electrons, it becomes an ion.
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