Ion

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.

page revision: 4, last edited: 13 Mar 2013 13:09