Gilbert Newton Lewis

(surrounded by pairs of

electrons)

Hybrid orbitals, Lewis diagrams, the octet rule

ReviewReview• We can visualize a covalent bond as a

balance between attraction and repulsion• A second way to view the formation of a

bond is to consider orbital diagrams• Video (15 min - stop at HCl)• Now we can visualize atoms bonding

because of the lower energy achieved via the stability of filled valence shells

• The bottom line: atoms gain, lose, or share electrons to obtain noble gas electron configurations

Video: filling subshellsVideo: filling subshells

Video: filling subshellsVideo: filling subshells

•Draw orbital diagrams for F + F, H + O, Li + F

Overlapping orbitalsOverlapping orbitals• Draw orbital diagrams for F + F, H + O, Li + F

1s 2s 2p

1s2s2p

1s 2s 2p

1s

1s

F2

H2O

1s 2s 1s2s2p

LiF is ionic (metal + non-metal)

Hybrid orbitalsHybrid orbitals• Two overlapping orbitals form what is known

as a hybrid or molecular orbital• Just as in a s,p,d, or f orbital the electrons can

be anywhere in the orbital (even though the electron has started out in one atom, at times, it may be closer to the other nucleus)

• Each hybrid orbital has a specific shape (described in chapter 8)

• You do not need to know shapes• You need to know that hybrid orbitals exist

and that they are formed from overlapping orbitals

Lewis diagramsLewis diagrams• Read Pg. 229. Draw Lewis dot diagrams for

Ne, Sb, Rb, F. How many variations of the Lewis diagram for P can be drawn?

Ne Sb Rb F

P P P P

• Lewis diagrams follow the octet rule: atoms when forming ions, or bonding to other atoms in compounds have 8 outer electrons

• Q - How can the octet rule be explained?• A - s (2 e–) and p (6 e–) orbitals are filled

Cl– Na+ Cl–

Ionic bondingIonic bonding• Recall: Ionic bonding involves 3 steps:

1) loss of e-, 2) gain of e-, 3) +ve, -ve attract

Na Cl

e–1) 2)

3)

Na+

This can be represented via Lewis diagrams…• Read remainder of 7.2 (pg. 230)• Diagram the reaction between Li + Cl and Mg + O (PE 3)

The octet rule (ionic compounds)The octet rule (ionic compounds)• Draw Li + Cl and Mg + O (PE 3, pg. 230)

Li Cl [ Cl ]–[Li]+

[ O ]2–[Mg]2+OMg

• Note also that the charge on an ion can be determined by the number of places removed from a noble gas (Ca, N, Al?)

• Ca2+, N3-, Al3+

• See pg. 230 for example of Ca + Cl

Covalent bondingCovalent bonding• Covalent bonds can also be shown via Lewis

diagrams - E.g draw Lewis diagrams showing the combination of 1) H+Cl, 2) C+Cl, 3) H+O, 4) Mg+F, 5) N+H, 6) Do PE 4 (pg. 234)

HCl

H Cl

CCl4

C

Cl

Cl

Cl

Cl H2OH O H

MgF2 - Ionic

[ F ]2– [Mg]2+

NH3

H N H

H

• Note bonds can also be drawn with a dash to represent two electrons (read 234-5 upto 7.5)

The octet rule (covalent compounds)The octet rule (covalent compounds)• (Read 7.4 up to PE4 (pg. 232 - 4). Do PE4.)• Read remainder of 7.4• Although the octet rule works for most

compounds, PCl5 and SF6 are examples of exceptions (see pg. 235 for structures)

• Also, it can be difficult to draw the correct bonds for atoms with multiple bonds

• Some clear rules have been established for drawing Lewis structures

• We will see that the rules dictate molecular structure, which dictates shape, which can influence chemical properties of a compoundFor more lessons, visit

www.chalkbored.com