1. Writing Formulas 8 th gr. Chemistry

2. Warm-up What is a molecule? a. A particle that breaks apart when heated or expands when frozen. b. A substance made of two or more atoms bonded together. c. A substance that changes its structure when it becomes a solid, liquid, or gas.

3. Discuss Water is a molecule; what is its formula? H 2 0 2 H 2 0 HO 2

4. Oxidation number aka ionic charge - a number that represents the number of electrons lost or gained by an atom when it chemically bonds to another. Ion- is a charged particle that has more or less electrons than protons.

5. Label your table with the oxidation numbers Alkali metals +1 Alkaline Earth metals +2 Boron family +3 Carbon family +/- 4 Nitrogen family -3 Oxygen family -2 Halogen family -1

6. Discuss Why doesn’t the Noble gas family have an oxidation number?

7. A: The Noble gas family is inert and they do not chemically combine with or bond with others to make compounds.

8. If the Oxidation # is (+) then the element loses electrons when it bonds. Aka Cation If the Oxidation # is (-) then the element gains electrons when it bonds. Aka Anion

9. Metals lose electrons when they bond Nonmetals gain electrons when they bond

10. Rules for writing formulas for binary compounds (compounds made of two elements) Write the symbol of the element with the positive oxidation number first. calcium Write the negative next. oxygen Add subscripts so that the SUM of the oxidation number equals ZERO Ca 2+ O 2- = CaO Ca 2+ Cl 1- = CaCl 2

11. Rules for writing names for binary compounds Write the name of the positive ion first Check to see if the positive ion has more than one oxidation number. If it does write the number using roman numerals in parentheses after the ion’s name. Write the root name of the negative ion (for chlorine the root is chlor ) Add the ending –ide