Part 1:Lewis Dot Diagrams and

Structures

Lesson 4 – Lewis Diagrams and Molecular Geometry

Review of Chemical BondsReview of Chemical Bonds There are 3 forms of bonding:There are 3 forms of bonding: __________________—complete —complete transfer transfer of 1 or more of 1 or more

electrons from one atom to another (one electrons from one atom to another (one loses, the other gains) forming oppositely loses, the other gains) forming oppositely charged ions that attract one anothercharged ions that attract one another

__________________—some valence electrons —some valence electrons sharedshared between atoms between atoms

_________ – holds atoms of a metal _________ – holds atoms of a metal togethertogether

The type of bond can The type of bond can usuallyusually be be calculated by finding the difference in calculated by finding the difference in electronegativity of the two atoms that are electronegativity of the two atoms that are going together.going together.

Electronegativity Difference If the difference in electronegativities is

between:

– ≥ 2.0: Ionic

– 0.>0.4 to < 2.0: Polar Covalent

– 0.0 to 0.4: Non-Polar Covalent

Example: NaClNa = 0.8, Cl = 3.0Difference is 2.2, sothis is an ionic bond!

Review of Valence ElectronsReview of Valence ElectronsReview of Valence ElectronsReview of Valence Electrons Remember from the electron Remember from the electron

arrangement that valence electrons arrangement that valence electrons are the electrons in the OUTERMOST are the electrons in the OUTERMOST energy level. energy level.

BB is is 1s1s22 2s 2s22 2p 2p11; so the outer energy ; so the outer energy level is 2, and there are 2+1 = 3 level is 2, and there are 2+1 = 3 electrons in level 2. These are the electrons in level 2. These are the valence electrons!valence electrons!

BrBr is is [Ar] 4s[Ar] 4s22 3d 3d1010 4p 4p55

How many valence electrons are How many valence electrons are present?present?

Lewis Dot Diagrams A way of keeping track of

valence electrons in ionic compounds.

How to write them? Write the symbol. Put one dot for each

valence electron Don’t pair up until they

have to (Hund’s rule)

X

The Lewis Dot diagram for Nitrogen

Nitrogen has 5 valence electrons.

First we write the symbol.

NThen add 1 electron at a time to each side.Until they are forced to pair up.

Lewis Dots For Cations Metals will have few valence

electrons (usually 3 or less)

Ca

Lewis Dots For Cations Metals will have few valence electrons These will come off

Ca

Lewis Dots For Cations Metals will have few valence electrons These will come off Forming positive ions

Ca2+Pseudo-noble gas configuration

Lewis Dots For Anions Nonmetals will have many valence

electrons (usually 5 or more) They will gain electrons to fill outer shell.

P P3-

Ionic Bonding Anions and cations are held

together by opposite charges. The bond is formed through the

transfer of electrons. Electrons are transferred to achieve

noble gas configuration (octet rule).

Lewis Dot Diagrams Ionic Bonding

Na Cl

Lewis Dot Diagrams Ionic Bonding

Na+ Cl-

Lewis Dot Diagrams Ionic Bonding

All the electrons must be accounted for!

Ca P

Lewis Dot Diagrams-Ionic Bonding

Ca P

Lewis Dot Diagrams Ionic Bonding

Ca2+ P

Lewis Dot Diagrams Ionic Bonding

Ca2+ P

Ca

Lewis Dot Diagrams Ionic Bonding

Ca2+ P 3-

Ca

Lewis Dot Diagrams Ionic Bonding

Ca2+ P 3-

Ca P

Lewis Dot Diagrams Ionic Bonding

Ca2+ P 3-

Ca2+ P

Lewis Dot Diagrams Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ca

Lewis Dot Diagram Ionic Bonding

Ca2+ P 3-

Ca2+ P

Ca

Ionic Bonding

Ca2+ P 3-

Ca2+P

3-

Ca2+

Lewis Dot Diagram Ionic Bonding

= Ca3P2Formula Unit

Lewis Structures –Covalent Bonding

Covalent bonds Nonmetals hold on to their valence

electrons. Still want noble gas configuration. By sharing, both atoms get to count the

electrons toward a noble gas configuration.

Covalent bonding Fluorine has seven valence

electrons

F

Covalent bonding Fluorine has seven valence

electrons A second atom also has seven

F F

Covalent bonding Fluorine has seven valence

electrons A second atom also has seven By sharing electrons…

F F

Covalent bonding Fluorine has seven valence

electrons A second atom also has seven By sharing electrons…

F F

Covalent bonding Fluorine has seven valence

electrons A second atom also has seven By sharing electrons…

F F

Covalent bonding Fluorine has seven valence

electrons A second atom also has seven By sharing electrons…

F F

Covalent bonding Fluorine has seven valence

electrons A second atom also has seven By sharing electrons…

F F

Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… …both end with full orbitals

F F

Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… …both end with full orbitals

F F8 Valence electrons

Drawing Lewis Structures Find total # of valence e-.

Arrange atoms - singular atom is usually in the middle.

Form bonds between atoms (2 e-).

Distribute remaining e- to give each atom an octet

If there aren’t enough e- to go around, form double or triple bonds.

Water

H

O

Each hydrogen has 1 valence

Electron (Total of 2e)

Each hydrogen wants 1 more

The oxygen has 6 valence electrons

The oxygen wants 2 more

They share to make each other happy

Water Put the pieces together (8 e to distribute). The first hydrogen is happy The oxygen still wants one more

H O

Water The second hydrogen attaches Every atom has full energy levels Remember to check count.

H OH

Drawing Lewis Structures CF4

1 C × 4e- = 4e-

4 F × 7e- = 28e-

32e- FF C F

F

- 8e-

24e-

Drawing Lewis Structures BeCl2

1 Be × 2e- = 2e-

2 Cl × 7e- = 14e-

16e-

Cl Be Cl - 4e-

12e-

Multiple Bonds Sometimes atoms share more than

one pair of valence electrons. A double bond is when atoms share

two pairs (4 total) of electrons A triple bond is when atoms share

three pairs (6 total) of electrons Know which elements are diatomic

(Oxygen?)

Carbon dioxide CO2 - Carbon is central

atom ( more metallic ) Carbon has 4 valence

electrons Oxygen has 6 valence

electrons (total of 12e) 16e must be distributed.O

C

Carbon dioxide Attaching 1 oxygen leaves the

oxygen 1 short, and the carbon 3 short

OC

Carbon dioxide Attaching the second oxygen leaves both

oxygen 1 short and the carbon 2 short IF the central atom is not surrounded by 4

electron pairs, it does not have an octet. You must convert one or more of the lone pairs on the terminal atoms to a double or triple bonds.

OCO

Carbon dioxide The only solution is to share more

OCO

Carbon dioxide The only solution is to share more

OCO

Carbon dioxide The only solution is to share more

OCO

Carbon dioxide The only solution is to share more

OCO

Carbon dioxide The only solution is to share more

OCO

Carbon dioxide The only solution is to share more

OCO

Carbon dioxide The only solution is to share more Requires two double bonds Each atom can count all the

electrons in the bond

OCO

Carbon dioxide The only solution is to share more Requires two double bonds Each atom can count all the electrons in the

bond Count e’s

OCO8 valence electrons

Carbon dioxide The only solution is to share more Requires two double bonds Each atom can count all the electrons in

the bond

OCO8 valence electrons