Drawing Lewis Dot Structures!! 1) MEMORIZE the # valence electrons for C, H, O, N, Cl and related elements! 2) KNOW the octet (or duet) rule!!
How many nonbonding electrons are in methane, ammonia, water, and HCl?
C.... How many bonds will form? REVIEW
C H H H H Methane, CH 4 4 bonds around C (8 electrons) REVIEW
N N How many bonds are likely to form?
Ammonia, NH 3 H H H N 3 bonds around N Note the nonbonding pair.
O How many bonds?
Water O — H H 2 bonds around O How many nonbondin g pairs?
Cl Cl How many bonds is Cl likely to form?
Hydrogen chloride H — Cl H — Cl 1 bond from Cl 1 bond from Cl How many nonbondin g pairs?
What happens to CFCs when they get into the atmosphere?
FREON-12 (dichlorodifluoromethane) C Cl F F UV-C What does UV light usually do to bonds? C Cl F F. +. Don’t forget about the nonbonding electrons!
CCl 2 F 2 λ < 220 nm UV-C light. CClF 2 +Cl.
Where in the atmosphere does this take place?
What is the difference between Cl. And Cl - ? Cl. Cl - Chlorine radicalChloride ion Draw the Lewis structure for each! What do we do with the charge? :Cl... :Cl:.. - Which one is more reactive? Why????
Be able to write the same thing for OH. and OH -1 Which is more reactive? Why? ON YOUR OWN
Write the complete reaction for the ionization of H 2 O in Lewis structure form!! H 2 O vs H 2 O.+ Don’t forget the nonbonding electrons! ON YOUR OWN Which is more reactive? Why?
Why do CO and N 2 look the same? 1. Count the valence electrons 2. Follow the octet rule! ON YOUR OWN
Be able to complete this worksheet from all directions!
Handout C! (resonance forms!)
Handout C Be careful of resonance forms!
Resonance Sometimes just one Lewis structure cannot completely describe the actual chemical structure…
Sometimes one Lewis structure cannot completely describe the structure… Resonance structures will always involve a double bond!
Look at Handout C!
Resonance - EXAMPLE AHEAD
OO O.. Ozone, O 3 How many valence electrons? Is this the only way we could write this structure?
OO O OO O.. OR They are both equal! Neither ONE is correct!
Resonance structures for O 3 OO O [ [ OO O.. No one resonance form actually represents the true structure of ozone.
Actual structure for ozone… O O O An average of the two resonance structures
Compare with O 2 O=O O=O oxygenozone oxygenozone O O O Which bond is stronger?
O 2 O + O O 2 O + O λ< 242 nm λ< 242 nm O 3 O 2 + O O 3 O 2 + O λ< 320 nm λ< 320 nm UV- C UV- B
Try the rest of the worksheet on your own! HINT: SO 2 will look a lot like ozone… WHY? HINT: Don’t forget the charge on nitrate!
Benzene C 6 H 6 A hydrocarbon How many valence electrons?
Fig.10.04a Figure 10.4 p. 438
Fig.10.04b Figure 10.4 p. 438
Fig.10.04b Figure 10.4 p. 438 Is there any other way to draw this structure?
So, how do we usually draw benzene? How many bonds are between each carbon?
Fig.10.04d Figure 10.4 p. 438
Fig.10.04c Figure 10.4 p. 438
What is ANOTHER way that atoms can differ?? Their “greediness” for electrons.
Electronegativity – the measure of an atom’s attraction for electrons in a chemical bond (CiC)! Every element has its own electronegativity ! (RANGES FROM 0 to 4)
Electronegativity: Increases to the right and up the periodic table! WHY? (RANGES FROM 0 to 4)
Why do we worry about electronegativity ?
Covalent Bonds O=C=O C H H H H C H H H H ::. O::OC:: A bond where two atoms share electrons.. methane, CH 4 carbon dioxide, CO 2 Not all covalent bonds are created equal!!!
COVALENT BONDS NONPOLARPOLAR
TYPES OF BONDS Electronegativity Difference LowHigh IONICPOLARNONPOLAR COVALENT
Polar Bonds: Unequal sharing of electrons in a chemical bond. Still a covalent bond!
HCl EN H Cl High difference in EN! Cl pulls the electrons towards it! δ-δ- δ+δ+ Read as “delta minus” Means “slightly negative”
H — Cl or H :Cl H — Cl or H :Cl Unequal sharing of 2 electrons by 2 atoms. The bond in HCl is a polar bond.
HCl C H H H H EN H Cl C High difference in EN! HCl is a polar bond! δ-δ- δ+δ+ What about methane ? The C-H bond is nonpolar!
C H H H H ::. The electrons are shared (relatively) equally by the two atoms