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Notes for Oct 23 and Oct 24

Notes for Oct 23 and Oct 24. See examples on the last pages PLEASE!!! How to do the homework there!! Color coded to make it easier to follow… But is your print out in color?. Metals form Cations. Metals almost always lose their outer electrons, forming positive cations :

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Notes for Oct 23 and Oct 24

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  1. Notes for Oct 23 and Oct 24 See examples on the last pages PLEASE!!! How to do the homework there!! Color coded to make it easier to follow… But is your print out in color?

  2. Metals form Cations Metals almost always lose their outer electrons, forming positive cations: Na  Na+1 + 1 electron Ca  Ca+2 + 2 electrons Al  Al+3 + 3 electrons Each time, the metals lose their outermost valence electrons, and the energy level below is full.

  3. Nonmetals form Anions Nonmetals almost always gain electrons, and become negative anions. Cl + 1e-  Cl-1 Chlorine now has 18 e, just like Argon! O + 2e-  O-2 N + 3e-  N-3 Each time, the nonmetals gains the number of electrons needed to obtain 8 valence electrons.

  4. Oxidation Numbers • An oxidation number is the charge an atom would have if it became an ion. • Take out your Periodic Table and label the A Groups as follows. AND Silver = +1 Zinc = +2 Cadmium = +2

  5. Nomenclature • Nomenclature is a system for naming chemical compounds. • It has very specific rules you must follow. • We will start with the simplest type of ionic compound, a binary ionic compound. • Binary- means just two elements are present. • Ionic Bond--means a metal with a nonmetal

  6. Naming Binary Ionic Compounds 1. Name the metal first 2. Then name the nonmetal, with an “ide” ending. • Examples: NaCl Sodiumchloride LiBr Lithium bromide CaF2 Calcium fluoride

  7. Formula Writing for Binary Ionic Compounds • Sometimes you will be given the name of a compound and be asked to write the chemicalformula. • This requires three careful steps, and a periodic table. • Do not guess. Follow the steps! • “Almost right” is wrong!

  8. Formula Writing Example: Aluminum Oxide STEP 1: write the symbols, metal first, then nonmetal. Al O STEP 2: above each symbol, write the oxidation number Al+3 O-2 STEP 3: Add subscripts so that the overall charge of the compound is zero. (“criss-cross” + 6 and - 6 = 0) Step 4:(Erase the oxidation numbers, they are NOT part of the formula, they just help us get the correct subscripts!) Al2O3 +3 x 2 = +6 -2 x 3 = -6 subscripts

  9. EXTRA Example : Writing Formulas Al +3 Te -2 EX A . Aluminum telluride Step 1: Write the symbols and charges indicated by the compound name: Step 2: Criss Cross to figure out the subscripts --- See the colored arrows for the example shown here? ((Except when the charges match “opposite and equal” then we only need ONE of each ion… subscript “1” on each symbol.)) Step 3: Let’s prove our formula works: Aluminum’s side +3 x2 of them = +6 total charge on this side Telluride’s side -2 x3 of them = -6 total charge on that side The compound’s total charge = +6 + (-6) = ZERO ! Neutral… Because the compound’s total charge is zero, our formula is correct Magnesium sulfide Mg+2 S-2 ( +2 and -2match ! ) So, we only need “1” of each… Mg1S1 Al2 Te3

  10. Naming Easier Ionic Compounds Binary Compounds… 2 elements (the easiest) Step 1. Name the metal (without changing the name at all) Step 2. Name the nonmetal AND change its ending to “–ide”. Example Al2Te3 aluminum (tellurium becomes telluride) aluminum telluride Other Easy Ionic Compounds (sometimes we need to name polyatomic ions) Notice how “they” wrote carbonate… and other ions. They put the “charge” on top of the subscript of one of the elements… NASTY! I don’t like this at all… But I cannot change it. We need to learn to read it as it is… We write the carbonate ion as CO3-2 Do you see how their way actually does match ours… sort of? Do you see how other charges are the top number (Ex. PO4-3) Look at “acetate” I always use the first formula they list… Notice “ammonium” NH4+1is the ONLY polyatomic ion that is positive on the list.

  11. Naming Easier Ionic Compounds Binary Compounds… 2 elements (the easiest) Step 1. Name the metal (without changing the name at all) Step 2. Name the nonmetal AND change its ending to “–ide”. Example Al2Te3 aluminum (tellurium becomes telluride) aluminum telluride Other Easy Ionic Compounds (sometimes we need to name polyatomic ions) When you see THREE or more CAPITAL LETTERS, look for a POLYATOMIC ION. Ex. BeCO3 B, C, and O are capital … look for a polyatomic ion… 1st element…Be….. Not in any of the ions on the list. So that part is just “beryllium” Hunting for “C” in an ion now….…… find C2H3O2- (that’s not it)…. Ah! CO32- matches from the list! It’s called “carbonate”. [ Never change polyatomic ion names !!! ] NEVER! Now put it together… Berylliumcarbonate… done. ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Ex. NH4F (see three capital letters… a polyatomic ion is here) Look for an ion with “N”… NO2-1 …. NO3-1 “no, they don’t match”… NH4+1 that’s it! NH4+1 is ammonium F is a nonmetal that must change it’s ending to “-ide” “fluoride” Ammonium fluoride is the name we needed.

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