How Atoms BondChapter 17

1

Let’s Review

Electrons are

arranged in energy

levels

Electrons are

arranged in energy

levels

Electrons are

arranged in energy

levels

7

Take a Look at Helium

The Language of Chemistry

8

CHEMICAL ELEMENTS-pure substances that cannot be decomposed

by ordinary means to other substances

Symbols of Elements• Use 1 or 2 letter abbreviations• Capitalize the first letter only

• Examples–C Carbon Co Cobalt–N Nitrogen Ca Calcium–F Fluorine Br Bromine–O Oxygen Mg Magnesium

9

The Periodic Table

10

Dimitri Mendeleev

1834-1907

11

The Periodic Table

e

P

PN N

e

Helium

Atomic mass4 amu

He2

4.003

Atomic Number

Atomic Mass

12

The Periodic Table

e

P

PN N

e

Helium

Atomic mass4 amu

He2

4.003

Atomic Number

Atomic Mass

The way the table is organized tells a lot about the elements’ properties

Now… let’s combine all this information

…and watch what happens!

…and watch what happens!

You’ve built this in class!

The electrons in the outer rings are called “valence electrons”

Valence electrons play an important role an element’s ability to form

chemical bonds (chemical properties).

How many e- are in the outer rings? Do you see the valence patterns?

1 e- 2 e- 3 e- 4 e- 5 e- 6 e- 7 e- 8 e-ValenceElectrons

Gilbert Newton Lewis 1875-1946• Chemist at UC

Berkeley

• Exceptional teacher

• Productive researcher

• “Theory of Chemical Bonding”

• Lewis Dot Structures

Lewis Dot Structures

• Convenient• Easy way to understand

chemical bonding

Dot structures simplify this information

1 e- 2 e- 3 e- 4 e- 5 e- 6 e- 7 e- 8 e-ValenceElectrons

Dot structures only use the valence electrons

1 e- 2 e- 3 e- 4 e- 5 e- 6 e- 7 e- 8 e-ValenceElectrons

Watch….

H

Li1 e-Valence

Electrons1 e-Valence

Electrons

Try this….

1 e-ValenceElectrons

Na

1 e-ValenceElectrons

Look at Group 2….

2 e-ValenceElectrons

2 e-ValenceElectrons

Be

Mg

Group I3….

3 e-ValenceElectrons

3 e-ValenceElectrons

B

Al?

Group I4….

4 e-ValenceElectrons

4 e-ValenceElectrons

C

Silicon

Si

Group 15….

5 e-ValenceElectrons

5 e-ValenceElectrons

N

Phosphorous

P

Group 16….

6 e-ValenceElectrons

6 e-ValenceElectrons

O

S

Group 17….

7 e-ValenceElectrons

7 e-ValenceElectrons

Cl

F

Group 18….

8 e-ValenceElectrons

8 e-ValenceElectrons

Ne

He

35

Chemical Bonds

• Atoms can gain, lose or share electrons.

• Forces holding these atoms together are known as chemical bonds

36

Chemical Bonds

• Attraction between 2 or more atoms• Interaction between valence electrons

Ionic Bonds

Covalent Bonds

37

Valence Electrons

• Electrons in the highest (outer) level

Have most contact with other atoms

Known as valence electrons

• Outer shells of noble gases contain 8 valence electrons (except, He = 2)

Helium

Neon

Argon

38

Octet Rule

LecturePLUS Timberlake 7

Octet Rule

An octet in the outer shell makes atoms stable

Electrons are lost, gained or sharedto form an octet

Unpaired valence electrons strongly influence

bonding

So…

Chemical bonds are formed when atoms try to fill their outer electron shell and obey the octet rule.

39

Ionic Bonds• Attraction between oppositely charged ions

Using Lewis Dot Structures

Predicting Ionic Bonds

45

Salt

46

47

Covalent bonds form molecules

48

Double Covalent bonds