2. Chemical Symbols and formulas Suggested reading: Sections 5.1 - 5.4 of your text. What do we need to know in order to write formulas? What do we need to know in order to correctly name compounds?

3. Chemical Symbols and formulas Elements are represented by SYMBOLS: Na F Cu Compounds are represented by FORMULAS: NaCl CuSO 4 Al(NO 3 ) 3

4. Chemical Symbols and formulas Chemists combine element symbols into chemical formulas to represent compounds (two or more elements combined) NaCl AlPO 4 Polyatomic ion!!

5. Chemical Symbols and formulas A formula shows two things: The kinds of elements in the compound AND The number of elements in the compound! Na 1 sodium atom Cl 1 chlorine atom AlPO 4 1 aluminum atom 1 phosphoru s atom 4 oxygen atoms!

6. More information about those little numbers in the formulas…. Chemical Symbols and formulas Al PO 4 When only one atom of an element is present, no number is used. SUBSCRIPT If more than one atom of an element is present, we state how many.

7. Chemical Symbols and formulas How many atoms are present in these compounds? CuSO 4 1 Copper, 1 sulfur, 4 oxygen HFHF1 hydrogen, 1 fluorine NH 4 Cl1 nitrogen, 4 hydrogen, 1 chlorine

8. Chemical Symbols and formulas Is that all there is to it? NOPE. Mg(NO 3 ) 2 1 magnesium…… 2 nitrogen…… 6 oxygen!! There are TWO nitrate ions here. (NO 3 ) is the polyatomic ion ‘nitrate’ remember! Everything INSIDE the parenthesis must be multiplied by the number OUTSIDE the parenthesis.

9. Chemical Symbols and formulas In order to write formulas and correctly name compounds we need to know something about Periodic table Electrons And the

10. Chemical Symbols and formulas Atoms and their electrons I NEED 8 electrons in my outer shell! All atoms wish to have 8 electrons in their outer shells. They are willing to lose or gain electrons to achieve this number! 1 2 3 4

11. Chemical Symbols and formulas Atoms that are willing to LOSE their negatively charged electrons are called CATIONS. Na e- Good-bye little electron! I’m positive I’ll miss you! + Atoms that are willing to GAIN negatively charged electrons are called ANIONS. Cl 1 e- gained - This extra electron gives me 8 in my outer shell!

12. Chemical Symbols and formulas +1 +2 +3 +4 -4 -3-2 0 Cations (metals) Anions (non-metals)

13. Chemical Symbols and formulas This losing and gaining of electrons is why certain elements combine the way they do. Cations and anions must combine in a way that cancels out their + and - charges. Na + Cl - e- Here, have my electron! Why thanks, don’t mind if I do! e-

14. Chemical Symbols and formulas Na + Cl - And so they combined to live happily ever after…. Na LOST, Cl GAINED, and the compound is neutral (which means that all plusses and minuses cancelled!) I don’t need this old plus anymore! I don’t need this old minus anymore!