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 Chemists believe that many chemical compounds contain ions  Common Properties of these compounds: ◦ High melting point (ex: salt melt at 800*C) ◦ Tightly packed structure (Crystal Lattice) ◦ As a solid does not conduct but when melted is a good conductor ◦ Pure water does not conduct electricity but when the cmpd is dissolved in water, the solution conducts electricity. 2

3 The arrangement of sodium ions (Na + ) and chloride ions (Cl - ) in the ionic compound sodium chloride.

4 Solid sodium chloride highly magnified.

5 (a)Pure water does not conduct a current; (b) Water containing a dissolved salt conducts electricity

 A substance containing ions that can move can conduct electric current  Dissolving salt (NaCl) causes ions to be dispersed in the water  move freely  Some substances dissolve in water to form a solution that conducts well - these are called electrolytes  When dissolved in water, electrolyte compounds break up into component ions 6

 Ionic compounds – a compounds formed between a metal and a nonmetal  An ionic compounds must contain a net charge of ZERO  Must be composed of anions AND cations Total charge of cations + total charge of anions = Zero net charge 7

 Na + and Cl -  NaCl  Charge (+1) and (-1)  net 0  Mg 2+ and Cl -   Cation (+2) and Anion (-1)  Need 2 anions (-2) for Net 0 charge  Lithium and Nitrogen 8

 Chlorine and calcium  Sodium and sulfur  Calcium and phosphorus  Oxygen and barium 9

 ions that have a positive charge are called cations ◦ form when an atom loses electrons  ions that have a negative charge are called anions ◦ form when an atom gains electrons  ions with opposite charges attract ◦ therefore cations and anions attract each other  moving ions conduct electricity  compound must have no total charge, therefore we must balance the numbers of cations and anions in a compound to get 0 total charge 10