1. CHAPTER 20
CHEMICAL BONDING

2. Stability in Bonding
Most matter is found in compounds {ie air, water, salt}
Compounds have properties unlike those of their individual elements
Salt: NaCl= Na + Cl
Na is a grey, soft metal that reacts violently w/ water
Cl is a greenish-yellow gas that is toxic if inhaled
1 atom Na + 1 atom Cl = NaCl
NaCl is a chemical formula
Chemically combine to form something we put on our french fries!

3. H2O ≠ H2O ≠ H2O
Numbers in some chemical formulas are called subscripts
Means “written below”
This # tells how many atoms of that element combine with the other element(s)
Ammonia: NH3 = 1 N atom for every 3 H atoms 1N:3H ratio

4. Try these! SiO2 silicon dioxide C2H5OH ethanol H2SO4 sulfuric acid
C6H12O6 sugar
KMnO4 potassium permanganate

5. Chemical bonds are forces that hold atoms together in a compound
Chemical Formula: tells what elements it contains w/ symbols
Tells ratio of the atoms of those atoms w/ subscripts
Elements bond to become chemically stable (happy )
They become resistant to change
Outer E level completely filled with e- (usually 8 e-)
Gaining, losing, or sharing e- cause chemical change
Chemical bonds are forces that hold atoms together in a compound

6. 20-2 Types of Bonds Ions are atoms that have lost or gained an e-
This gives them a positive (+, lose e-) or negative (-, gain e-) charge
Draw Lewis structures for each element
Put brackets around the symbol [ ]
Then write a superscript + or – sign (see bottom of pg 609 or top of pg 603) outside of the brackets

7. Ionic Bonds
Force of attraction between the opposite charges of the ions in an ionic compound
Atoms gain or lose e- to become stable
Metals usually lose e- (# in outer E level)
Non-metals usually gain e-
Now both atoms are stable (happy )

8. Ionic bonding
NaCl
Whiteboard practice:
MgF2
CaCl2
LiBr KI
Mg3P2

9. Covalent bonding Molecules are formed when e- are SHARED
Sharing e- to become stable (8 e-/outer level) is more common than losing/gaining e-
Diatomic molecules: 2 atoms of the same element
Cl2 , O2 , H2 , N2 , F2
These would be nonpolar molecules: they share e- equally

10. Covalent bonding, cont.
e- not always shared equally: polar molecules are between 2 different non-metal elements
Unequal sharing causes the molecule to have a (+) and a (–) end
e- spend
more time
near the O
than the 2 H
atoms

11. CHEMICAL BONDING REVIEW
Ionic bonding forms ions which can be positive or negative
Covalent bonding forms molecules which can be polar or non-polar
Elements that are close together on the periodic table (non-metals) usually form covalent bonds
Elements far apart on the periodic table (metals & non-metals) form ionic bonds
Extra Credit!!! Draw dot diagram for sugar:
C6 H12 O6

12. 20.3 Writing Formulas and Naming Compounds
Oxidation # is a + or - # assigned to an element to show its combining ability in a compound
It indicates how many e- an atom has lost, gained or shared when bonding
NaCl: Na loses 1 e- : 1+ oxidation #
Cl gains 1 e- : 1- oxidation #
Write the oxidation #’s on your periodic table from pg 616

13. Some elements have more than 1 oxidation #
Usually the Transition elements
Use Roman numerals to show the different oxidation #’s
Copy Table 2 from pg 616 onto the back of your periodic table
Do the same for Table 3, pg 618 and Table 4, pg 619 and Table 5, pg 621

14. How to write binary ionic formulas
Binary compound: composed of 2 different elements (ie NaCl)
1) write the symbol for the elements w/ the (+) oxidation # (H & metals are +)
2) then write the symbol of the element w/ the (-) oxidation # (non-metals)
3) add subscripts so the sum of the oxidation #’s of the atoms are zero

15. Let’s Practice! Bromine and Potassium 1) Potassium is + : K1+
2) Bromine is - : Br1-
3) (1+) + (1-) = 0, so no subscripts are needed
4) KBr
Nitrogen and Magnesium
1) Magnesium is + : Mg2+
2) Nitrogen is - : N3-
3) (2+) + (3-) ≠ 0, so you need to add subscripts
4) Use crossover method: the ox# of Mg becomes the subscript for N; ox# of N becomes the subscript for Mg: Mg3N2
DO NOT USE + OR – SIGN IN SUBSCRIPT!!!

16. PRACTICE WITH WHITEBOARDS
Flourine and Lithium
Chlorine and Aluminum
Calcium and Oxygen
Oxygen and Sodium
Potassium and Chlorine
Strontium and Sulfur
Beryllium and Nitrogen
Iodine and Rubidium

17. Naming chemical compounds
1) Write the name of the (+) element
2) If this element has more than 1 ox # (check the back of your periodic table), use the ox # of the (-) element to figure out the ox # of the (+) element; use a Roman numeral after the element’s name
3) use Table 3 (back of your PT) to name the second element

18. Let’s Practice!
CuI
1) Cu is (+) : Copper (is it a ‘special ion’? Look on the back of your PT)
2) I is (-) : it’s ox # is (1-), so we should use Copper (I)
3) I is iodine, which changes to iodide in binary compounds
4) Copper (I) iodide

19. WHITEBOARD PRACTICE
MgF2
PbO2
Na2O
LiBr
BaS
CuO
FeF3
Cr2O3

20. Compounds with Polyatomic Ions
Poly: many, so polyatomic: having many atoms
Polyatomic ion: positively or negatively charge group of atoms that act as one when bonding
Table 4 is just a short list

21. Naming with polyatomic ions
1) Write positive part first
2) Use Table 4 from the back of your PT
Example: NaOH
1) Na is positive: sodium
2) OH : hydroxide
3) sodium hydroxide

22. Whiteboard practice Cu(OH)2 CaCO3 Al(C2H3O2)3 (NH4)3PO4 CuSO4
Ba(ClO3)2
NH4Cl
PbCO3

23. Writing formulas w/ polyatomics
Same rules as for binary compounds
Plus step 4: write parentheses around polyatomic ion when more than one of that ion is needed
Example: iron III nitrate
1) iron (III) = Fe3+
2) nitrate = NO3 1-
3) You will need 3 (NO3) to make ox #’s = zero
4) Subscript is written outside the ( ) otherwise it would look like FeNO33
Fe(NO3)3

24. WHITEBOARD PRACTICE!! Potassium chlorate Ammonium chloride
Sodium sulfate
Magnesium chlorate
Lead (II) carbonate
Chromium (III) phosphate
Lithium nitrate
Calcium acetate

25. Compounds with added water
Hydrate is a compound that has water chemically attached to its ions
CoCl2·6H2O: Cobalt chloride hexahydrate
Hexa= 6; hydrate= H2O
Ca(NO3)2·3H2O : ?
Mg3(PO4)2·4H20 : ?