An ion is a charged particle - an atom or molecule where the number of protons and the number of electrons are not equal.

Cations and Anions

  • Cations are positively charged ions, where protons > electrons
  • Anions are negatively charged ions, where electrons > protons

Metals (especially to the left) form Cations. Group 1 lose 1 electron to become +1, Group 2 lose 2 electrons to become 2+, etc.

Group 17 gains an electron to form an anion -1, and so on.

Nonmentals in groups 13-15, and the transition metals, have several oxidation states.

Nuclear Arithmetic Examples

  • Mg2+ - how many electrons?
    • Magnesium is 12 on the periodic table, and must have 12 protons to be so. Hence there must be 2 less electrons, and hence has 10 electrons.
  • Write out an ion with number 17 and 18 neutrons and electrons
    • 17 is Chlorine - CL. If it has one extra neutron and electron we must adjust the atomic weight (from 34 to 35) and add a minus = 35Cl-

Polyatomic Ions

Polyatomic Ions are charged compounds.

Ions in Solution

In an ionic solid the ions are bonded together strongly, due to their opposite charge.

However these bonds dissolve in water because the H2O acts as a solvent, forming stronger bonds with each ion than they had with each other.

Hence ions in solution dissolve and separate into their component elements.