The Octet Rule

All atoms “want” a full valence shell of e-

This makes them more stable, like the Noble Gases, which have 8e-, a full valence shell.

For H and He a full valence shell is 2 e-

For all bigger atoms, a full valence shell is

8 e- (hence “octet”)

The Octet Rule

All atoms “want” their valence shell to mimic a Noble Gas e- configuration:

Most chemical reactions are the result of atoms gaining or losing or sharing e- with other atoms in order to have 8 valence e-

Covalent Bonding

Definition: two or more atoms sharing valence e- so that each atom has a full valence shell (2 e- for H and He, 8 e- for all bigger atoms)

H Cl

Covalent Bonding

Definition: two or more atoms sharing valence e- so that each atom has a full valence shell (2 e- for H and He, 8 e- for all bigger atoms)

ClH

When does covalent bonding occur?

1) Between elements that are non metals

2) Between two elements with an electronegativity difference of less than

1.7

How do I find the electronegativity difference between 2 atoms?

Using Table S, look up the electronegativity values for each atom. Then find the difference by subtracting the smaller value from the bigger value:

H = 2.1 Cl = 3.2 Electronagativity difference = 3.2 -2.1 = 1.1Since 1.1 is less than 1.7, this bond is covalent

Forming a Covalent Bond

Non- polar covalent bonds

NON POLAR covalent bonds occur when the electronegativity difference of the two bonded atoms is zero.

When does this happen?

When the two bonded atoms are identical

Non- polar covalent bonds

All Diatomic atoms have non-polar covalent bonds:

H2 N2 O2 F2 Cl2 Br2 I2

Non- polar covalent bonds

In a non polar covalent bond, the shared electrons are shared equally between both atoms

This means they spend equal amounts of time orbiting both nuclei

Double covalent bonds

Some atoms can share TWO electrons with another atom. This results in a double bond.

OO

Each oxygen atom has 6 valence e-

By sharing 2 e- pairs, they will each fill their

Valence shell with 8 e-

Double covalent bonds

OO

Each oxygen atom has 6 valence e-

By sharing 2 e- pairs, they will each fill their

Valence shell with 8 e-

Double bond

Lewis dots can get tedious to draw for double bonds, so often the “stick” model is used instead:

One represents a shared pair of e-

O O

Triple covalent bonds

Some atoms, like nitrogen, can form a triple covalent bond with other atoms

Each atom shares 3 of its valence e-

N N

POLAR covalent bonds

Except for diatomic molecules, most covalent bonds are POLAR

This means one atom is more electronegative than the other, and the e- are NOT SHARED EQUALLY

The e- spend more time near the nucleus of the more electronegative atom

H Cl

Since Cl is more electronegative than H,

The H-CL bond is polar

Since the shared e- spend more time near the

Cl nucleus, the Cl side of the molecule has a

partially negative charge

-+

The H side has a partially positive charge

The whole molecule is neutral

Water Molecule

The water molecule H20 has polar covalent bonds between the O and H.

The shape of the molecule is also important:

It looks like Mickey Mouse

Water Molecule

The Mickey Mouse shape also makes the molecule polar: The O end is partially negative, and the H end partially positive

+

_

The non-bonding

e- are called

“lone pairs”

XX X

The bonding e-

are called the

“shared pairs”

Polar Molecules

Just because a molecule contains polar bonds does not mean the molecule itself is POLAR, like water.

C=O=C carbon dioxide has polar bonds between C

and O but the symmetrical shape eliminates the polarity of the whole molecule

Molecules

Atoms bonded together by covalent bonds form MOLECULES

Molecules are the smallest discrete particle of an element or compound formed by covalently bonded atoms

Molecules

Each atom in a molecule usually has 8 valence e- (a noble gas e- configuration)

Covalent molecules make up Molecular Substances

Water is a molecular substance

Molecular Substances

Properties of molecular substances:

1) Soft (like butter)

2) Poor conductors of electricity and heat

3) Low melting points (melt easily)

4) Low boiling points (boil easily)

Metallic Bonding

Metallic Bonds

Are a special type of bond between metal atoms of the same element

These bonds are characterized as:

Positive ions (the kernel) immersed in sea of mobile (valence) electrons

The kernel is the nucleus and the non-valence e-

Metallic Bond: Positive ions immersed in a sea of mobile

electrons

+ + +

+ + +

- --

-

-

-

--

-

- --

-

-

- -

Metallic Bonds

The valence e- in a metal bond are free to move between the different atoms.

These MOBILE ELECTRONS give metals the ability to conduct electricity and heat

Also the metallic properties of malleabilty and ductility