StarterStarter

Which elements naturally exist as Which elements naturally exist as diatomic molecules?diatomic molecules? Remember, the 7 + 1 ruleRemember, the 7 + 1 rule

How many valence electrons do each How many valence electrons do each of the halogens have? of the halogens have?

Octet RuleOctet Rule

representative elements can “fill” their representative elements can “fill” their outer energy level by sharing outer energy level by sharing electrons in covalent bondselectrons in covalent bonds

Octet Rule-Octet Rule- a compound tends to form a compound tends to form so that each atom has an octet (8) of so that each atom has an octet (8) of electrons in its highest energy level by electrons in its highest energy level by gaining, losing or sharing electronsgaining, losing or sharing electrons

Duet Rule-Duet Rule- applies to H and He applies to H and He

Octet RuleOctet Rule Less than 8:Less than 8:

Boron: 6 in outer energy levelBoron: 6 in outer energy level More than 8:More than 8:

anything in 3anything in 3rdrd period or heavier period or heavier because may use the empty d orbital because may use the empty d orbital ex: S, P, Iex: S, P, I

Electron Dot DiagramsElectron Dot Diagrams a way to show electron configurationa way to show electron configuration identifies the number and pairing of identifies the number and pairing of

valence electrons to show how valence electrons to show how bonding will occurbonding will occur

1.1. write the noble gas notationwrite the noble gas notation

2.2. identify the number of valenceidentify the number of valence

3.3. identify how many are paired and identify how many are paired and how many are alonehow many are alone

4.4. do not go by Figure 6-10do not go by Figure 6-10

ExampleExample

NitrogenNitrogen 1s1s2 2 2s2s2 2 2p2p33

5 valence5 valence 2 are paired2 are paired 3 are alone3 are alone

SulfurSulfur 1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p44

6 valence6 valence 4 paired (2 pairs)4 paired (2 pairs) 2 are alone2 are alone

N

Lewis StructuresLewis Structures

like dot diagrams but for entire like dot diagrams but for entire moleculesmolecules

atomic symbols represent nucleus atomic symbols represent nucleus and core electrons and dots or and core electrons and dots or dashes represent valence electronsdashes represent valence electrons unshared electrons: (lone pairs) pair of unshared electrons: (lone pairs) pair of

electrons not involved in bonding electrons not involved in bonding written around only one symbolwritten around only one symbol

bonding electrons: written in between 2 bonding electrons: written in between 2 atoms as a dashatoms as a dash

Types of Bonds Types of Bonds

single-single- sharing of one pair of electrons sharing of one pair of electrons weakest, longestweakest, longest

doubledouble- sharing of 2 pairs of electrons- sharing of 2 pairs of electrons stronger and shorterstronger and shorter

triple-triple- sharing of 3 pairs of electrons sharing of 3 pairs of electrons strongest and shorteststrongest and shortest

multiple bonds include double and multiple bonds include double and triple bondstriple bonds

Drawing Lewis StructuresDrawing Lewis Structures

1.1. find the number of valence electrons find the number of valence electrons in each atom and add them upin each atom and add them up

2.2. draw the atoms next to each other in draw the atoms next to each other in the way they will bondthe way they will bond

3.3. add one bonding pair between each add one bonding pair between each connected atomsconnected atoms

4.4. add the rest of the electrons until all add the rest of the electrons until all have 8 have 8 (consider exceptions to octet rule)(consider exceptions to octet rule)

H

H C Cl

H

Example 1Example 1CHCH33ClCl

methyl chloridemethyl chloride

C: 4 x 1 = 4C: 4 x 1 = 4 H: 1 x 3 = 3H: 1 x 3 = 3 Cl: 7 x 1 = 7Cl: 7 x 1 = 7 total = 14 electronstotal = 14 electrons carbon is centralcarbon is central

H

H C Cl

H

duet

duet

duet

octetoctet

Example 2Example 2NHNH33

ammoniaammonia

N: 5 x 1 = 5N: 5 x 1 = 5 H: 1 x 3 = 3H: 1 x 3 = 3 total = 8total = 8

N is centralN is central

H N H

H

Example 3Example 3

NN22

nitrogen gasnitrogen gas

N: 5 x 2 = 10N: 5 x 2 = 10 10 electrons10 electrons

N N

N N

Example 4Example 4

CHCH22OO formaldehydeformaldehyde C: 4 x 1 = 4C: 4 x 1 = 4 H: 1 x 2 = 2H: 1 x 2 = 2 O: 1 x 6 = 6O: 1 x 6 = 6 total = 12total = 12 C is centralC is central

H C H

O

Example 5Example 5

OO33 ozoneozone O: 6 x 3 = 18O: 6 x 3 = 18 two completelytwo completely

equal equal arrangementsarrangements

the real structure the real structure is an average of these twois an average of these two

where each bond is sharing 3 electrons where each bond is sharing 3 electrons instead of 4 or 2instead of 4 or 2

O O O

O O O

Resonance StructuresResonance Structures

resonanceresonance – bonding between atoms – bonding between atoms that cannot be represented in on that cannot be represented in on Lewis structureLewis structure

show all possible structures with show all possible structures with double-ended arrow in between to double-ended arrow in between to show that electrons are delocalizedshow that electrons are delocalized

O O O O O O

Example 6Example 6NONO33

1-1-

N: 5 x 1 = 5N: 5 x 1 = 5 O: 6 x 3 = 18O: 6 x 3 = 18 total = 23 + 1 = 24total = 23 + 1 = 24

Covalent Network BondingCovalent Network Bonding

a different type of covalent bondinga different type of covalent bonding not specific moleculesnot specific molecules lots of nonmetal atoms covalently lots of nonmetal atoms covalently

bonded together in a network in all bonded together in a network in all directionsdirections

example:example: diamond diamond silicon dioxidesilicon dioxide graphitegraphite