Ionic bonding is a strong electrostatic attraction between oppositely charged ions. This is always between a metal and a non-metal. Metals from positive ions by donating elections from their outer-shell to a non-metal until it has a full outer shell.
For example, a potassium atom has one electron on its outer shell. A chlorine atom has seven electrons in its outer shell. These two elections react to form the compound potassium chloride which is held together by ionic bonding. The two ions both have full outer shells.
Ions always have a positive or negative charge. For example, those from group one will always loose an election, so will have a +1 charge. If you gain 3 elections, you will have a -3 charge.
If a group 1 and a group 7 atom reacted together, then there would be an overall charge of 0 because it would be a +1 and a -1 which equals 0.