 Electrically charged atoms or groups of atoms  Atoms gain or lose electrons, the protons remain constant  Example:  Sodium ion:11 protons (11+) 10 electrons (10-) The overall charge is 1+ or Na +

 Many atom ion  A group of atoms with an overall charge  Examples:  Nitrate NO 3 -1  Ammonium NH 4 +1

 Are composed of  + ions = cations  - ions = anions  Examples:NaCltable salt CaBr 2 calcium bromide

 The cation is always written first. This will always be the metal.  The ratio of charges should make the total electrical charge zero  Example:  Na + is combined with Cl -  The formula is NaCl, the ratio is 1:1

 Ca +2 is combined with Cl -  In this case, the charges are not the same  The formula becomes CaCl 2.  The ratio is 1:2

 Ba +2 is combined with nitrate NO 3 -1  Again, the charges are not equal  You will use parenthesis to change the number of nitrate ions present when bonded  The formula becomes Ba(NO 3 ) 2  The ratio here is 1:2

 Write the name of the first element  Write the name of the second element and change the ending to “–ide”  Example:  MgO = Magnesium oxide  K 2 S = Potassium sulfide

 Ionic bonding: Ionic bonding  Electron transfer  Results in an ionic compound  Between a metal and nonmetal or a polyatomic ion

Ionic compounds in equations are called formula units

 The ions are held together in crystals and the total positive charge equals the total negative charge.

 When ionic compounds dissolve in water, individual ions separate from each other and become “dispersed.” This is called an aqueous solution (aq)