# Chem 2 - Bonding and Calculations - Ions and Formulas

Revision cards for Ions and Formulas, hope this helps! :]

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## Ions and Formulas

Atoms that have lost or gained electrons are ions. Ions have the electronic structure of a Noble Gas (Group 0 - Helium, Neon, Argon, Krypton, Xenon, Radon)

The elements that most readily form ions are those in Groups 1, 2, 6, and 7. Group 1 and 2 elements are metals, and they lose electrons to form positive ions. Groups 6 and 7 elements are Non-metals, and they gain electrons to form negative ions

For example:

- Group 1 elements (Alkali metals) form ionic compounds with non-metals where the metal ion has a charge of +1 (Group 7 elements or 'Halogens') E.g K+Cl- (Potassium Chloride)

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## Ions and Formulas 2

Ionic compounds are made up of a positive and negative part

The overall charge of one therefore, is 0

So all the negative charges in the compound must balance all the positive charges

You can use the charges on individual ions to work out the formula for the ionic compound:

- Sodium Chloride contains Na+ (+1) and Cl- (-1) ions. (+1) + (-1) = 0. The charges are balanced with one of each ion, so the forumula is NaCl.

- Magesium chloride contains Mg2+ (+2) and Cl- (-1) ions. Because a chloride ion only has 1- charge we need two of them to balance the 2+ charge of a Magnesium ion. This gives us the formula MgCl2

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