 The goal of every atom is to become stable – most elements have partially filled outer shells and they must bond with another atom to become stable.  A compound is made up of at least 2 different elements that bond together.  Water (H 2 O), carbon dioxide (CO 2 ) and methane (CH 4 ) are compounds because each is made from more than one element.

 When a metal and a non-metal element bond together you get an Ionic Compound.  To know this – you simply look at your periodic table to determine if the elements are metals or non-metals.  IF BOTH elements are non-metal you are not dealing with an ionic compound.  If one is a metal (like sodium) and the other a non-metal (like fluorine), they will form an ionic compound (such as sodium fluoride, NaF).

 These types of compounds are made of ions (charged atoms).  They are held together by electrical attraction – positive and negative charges!

 We know that every atom in the first group on the periodic table has 1 valence electron.  These atoms become charged by giving away that electron and become positively charged +1. They become a Cation.  We know that every atom in group 17 is short 1 valence electron.  When these atom’s gain a valence electron they will carry a negative charge of -1. They become an Anion.

 Ions that are held together by a positive and negative charge are called Ionic Bonds.  Ionic Bonds are very strong – think of when you put two strong magnets together, it can be pretty difficult to pull them apart!

 Ionic compounds containing two different elements form when atoms from one element lose one or more valence electrons to atoms of the second element.  Table salt is an example of an ionic compound. Sodium and Chlorine ions come together to form Sodium Chloride, or NaCl. The sodium atom in this compound loses an electron to become Na+, while the chlorine atom gains an electron to become Cl-.

 Due to the strong electrostatic attraction, ionic compounds form regular and repeating patterns called lattices.

 Ions try to surround themselves with as many ions of opposite charge as closely as possible. Usually in the cube packing arrangement, the cation is just large enough to allow the anions to surround it without touching one another.

 High melting and boiling points - Ionic bonds are very strong - a lot of energy is needed to break them. So ionic compounds have high melting and boiling points. The melting point of Sodium Chloride is 801 °C.  Conductive when liquid - Ions are charged particles, but ionic compounds can only conduct electricity if their ions are free to move. Ionic compounds do not conduct electricity when they are solid - only when dissolved in water or melted. This is why they can make great insulators!