1. HOW TO WRITE THEM Formulas 1 st – Definition A symbolic representation of a compound or molecule

2. Why do they Combine? Atoms Strive to meet two conditions 1.To be neutral - By having the same # of electrons and Protons 2. Have the same # of electrons as a Noble gas - Being nonreactive is the most stable Can they have both at the same time? NO

3. Having the same number of electrons as a Noble gas is more desired They must gain or lose electrons - What would happen to their charge if they gained an electron? Negative - What would happen to their charge if they lost an electron? Positive

4. SOME DEFINITIONS - Ion – an atom that has a charge - Oxidation number – The charge an atom has is called it’s oxidation number. - Valence electrons – The number of electrons on the outside edge of an atom’s outer orbit - Maximum of eight How can there be only eight when some of the orbits can hold more than eight? Well...

5. Think of an orbit as having a thickness where: The 1 st orbit is only thin enough to hold 2 electrons The 2 nd orbit can only hold one thickness of 8 electrons But the 3 rd and the 4 th orbits are so thick that the electrons are spread out between the inside edge and the out side edge. 1 st 2 electrons 2nd 8 electrons 3 rd 18 electrons 4th 32 electrons Only eight can be on this outside edge and the rest are inside somewhere

6. Using the periodic table to know what charge an atom takes - Remember that the atoms want the same number of electrons as a Noble gas Examples Cl Protons Electrons Noble Gas Difference 8 7 11 12 9 35 101010101036 Subtract the noble gas electrons from the element electrons and that is the charge -2-3+1+2-1-1 ONNaMgFBr 18 17

7. Bellringer 11/19 1. DEFINE AN OXIDATION NUMBER. 1. DEFINE A SUBSCRIPT. 1. WHAT IS THE OXIDATION NUMBER FOR CHLORINE? *Keep this one in your notes. We will NOT be taking it for a grade!

8. +1 +2+3 -3-2 4

9. 1.SYMBOL: Write the symbol for each element 2.OXIDATION: Add their oxidation numbers 3.PLUS: Put a plus sign between the ions and add an arrow pointing to the right 4. FORMULA: Write the Formula so that the total net charge equals zero 5. BALANCE: Determine how many atoms of each to do this

10. SallySymbol OfferedOxidation PeterPlus FourFormula BananasBalance

11. For Example: -Combining Sodium and Chlorine 1. First write their symbols Na + Cl 2. Then add the oxidation numbers +1 3. Put a plus sign and draw an arrow pointing to the right 4. Write the formula (Positive is always 1 st ) NaCl The charges add up to be zero (balanced) (+1) + (-1)= 0 1. 2. 3. 4.

12. Another Example: Magnesium and Fluorine Mg + FMgF 2 +2 One Mg ion (+2) + Two F Ions (-1) + (-1) = 0 Remember the positive one first! One Mg plus two F charges will add up to be zero. - Subscript – The small number below and to the right of the symbol that denotes the number of atoms in a formula.

13. Practice Problems: 1.Potassium and Sulfur 2.Strontium and Bromine 3.Lithium and Oxygen 4.Calcium and Iodine 5.Aluminum and Chlorine 6.Gallium and Oxygen 7.Aluminum and Oxygen 8.Boron and Sulfur K +1 + S -2  K 2 S Sr +2 + Br -1  SrBr 2 Li +1 + O -2  Li 2 O Ca +2 + I -1  CaI 2 Al +3 + Cl -1  AlCl 3 Ga +3 + O -2  Ga 2 O 3 Al +3 + O -2  Al 2 O 3 B +3 + S -2  B 2 S 3

14. One more rule for the Transition Metals -Transition metals are called that because their ion charge can be one charge in one reaction and a different one in another -Since they are in a state of transition, it is unknown what charge they are for writing formulas - For this reason, a roman Numeral is assigned to represent the charge For example: Iron (III) would be written like this : Fe +3 and Cobalt (IV) would be written like this: Co +4

15. Here are the Roman numerals up to Fifteen : 1- I6- VI11. XI 2- II7- VII12. XII 3- III8- VIII13. XIII 4- IV9- IX14. XIV 5- V10- X15. XV -Roman Numerals tell you two things: -It is a Transition metal - It is a Positive Charge that matches the roman numeral

16. Practice Problems: 1.Iron (I) and Sulfur 2.Lead (IV) and Bromine 3.Cobalt (II) and Oxygen 4.Copper (II) and Iodine 5.Iron (III) and Chlorine 6.Mercury (I) and Oxygen 7.Copper (III) and Oxygen 8.Silver (II) and Sulfur Fe +1 + S -2  Fe 2 S Pb +4 + Br -1  PbBr 4 Co +2 + O -2  CoO Cu +2 + I -1  CuI 2 Fe +3 + Cl -1  FeCl 3 Hg +1 + O -2  Hg 2 O Cu +3 + O -2  Cu 2 O 3 Ag +2 + S -2  AgS

17. More Problems: Write the symbols with the charges, arrow, and final formula. O and H Li and Cl Na and Po K and Br Mg and I Ca and O Al and S Ca and F Fr and Te Ba and N Na and P Be and At