2. How ATOMS become IONS... REVIEW: An ion is an atom that has gained or lost electrons  A metal ion can lose electrons to form positive ions  A non-metal ion (except Noble Gases) can gain electrons and form negative ions Ions have the same arrangement of electrons as the nearest Noble Gas.

4.  The ion’s charge is shown on the element’s symbol Add a superscript number followed by a plus or minus sign

5. IONIC BONDING  Occurs when one or more electrons transfer from one atom to another; contain (+) and (-)ions  Recall: MgO Ionic compounds are made up of a metal and non-metal

6. Mg O 2 + 2 -

7. Writing the Formulas of Ionic Compounds Steps for Writing the Formula EXAMPLES Zinc NitrideAluminum Chloride 1. Identify each ion and its charge Zinc: Zn²+ Nitrogen: N³- Aluminum: Al³+ Chlorine: Cl - 2. Determine the total charges needed to balance positive with negative Zn²+: +2 +2 +2 = +6 N³-: -3 -3 = -6 Al³+: +3 = +3 Cl-: -1 -1 -1 = -3 3. Note the ratio of position ions to negative ions 3 Zn²+ ions for every 2 N³- ion 1 Al³+ ion for every 3 Cl- ion 4. Use subscripts to write the formula * “1” is NOT shown in subscripts! Zn ₃ N ₂ AlCl ₃

8. You try...  Li + with Cl –  Ca²+ with F-  Al³+ with O²-