Covalent Bonding

Molecular Bonds

Chemistry Joke

Q: What happened to the man who was stopped for having sodium chloride and a nine-volt in his car?

A: He was arrested for a salt and battery!

A little review… Ionic Bonds

Between a metal and a nonmetal The metal completely loses electrons that the

nonmetal gains. The elements are held together (bonded) by an

electrostatic charge, positive attracted to negative.

Lewis Dot Diagrams We use dots to represent the number of valence

electrons an atom has. Can have up to 8 electrons (dots).

A new kind of bond…

Fluorine has seven valence electrons.

F

A new kind of bond…

F F

A second F atom also has seven.

FF

Covalent bonding

FF

Covalent bonding

FF

Covalent bonding

F

Covalent bonding

F

Covalent bonding

F F

Covalent Bond

Covalent Bonding

By sharing electrons, both fluorine atoms end up with a full octet of electrons and stable orbitals.

F F

Covalent bonding

F F8 Valence electrons

By sharing electrons, both fluorine atoms end up with a full octet of electrons and stable orbitals.

Covalent bonding

F F8 Valence electrons

By sharing electrons, both fluorine atoms end up with a full octet of electrons and stable orbitals.

Covalent Bond A bond in which two atoms share

pairs of electrons so that each can achieve stability.

Covalent Compounds

• Made from 2 or more non-metals

• Are usually liquids and gases (or solids with low melting points)

Propane - C3H8

Covalent vs Ionic Compounds

• Chemical formulas called molecules.

• Nonmetal bonds with nonmetal.

• Chemical formula begins with a nonmetal.

• Bonds formed by sharing electron pairs.

• Chemical formula represents actual number of atoms in the compound.

• Chemical formulas called formula units.

• Metal bonds with nonmetal.

• Chemical formula begins with a metal.

• Bonds formed by attraction of positive cation to negative anion.

• Chemical formula represents the lowest whole # ratio of elements in the compound.

Covalent Ionic

Lewis Dot Diagrams

Remember: Atoms form compounds to create a full shell of valence electrons.

So, think Lewis Dot…

H H

O O

Hydrogen needs how many more electrons to have a filled energy level?

How many more electrons does oxygen need? 2

1

Water

H

O

Each H atom has 1 valence electron.

The O atom has 6 valence electrons.

Water

The first hydrogen wants one more electron.

The oxygen wants two more electrons.

H O

Water

H O

Water

H OCovalent bond

Water The first hydrogen is happy. A second hydrogen enters…

H OCovalent bond

H

Water

H OCovalent bond H

Water The second hydrogen attaches Every atom has stable energy

levels

H OH

We can use Lewis Dot Structures to represent covalent compounds!

1. Add up the valence electrons of all the atoms in the compound.

2. Write the symbols for the elements and connect them with a line(s).

a. Least electronegative element goes in the center (for example: carbon). H is always on the outside.

b. The other elements usually surround the center one.

3. Subtract 2 from the total for each line drawn and arrange the remaining electrons (dots) in pairs around the outer elements first so that each atom has an octet. (H likes 2. Boron is happy with 6.)

4. Check for happiness (stability)!

Example…NH3 Ammonia

H H H N

H H H N

N is surrounded by 8 electrons, and each H has 2 electrons. Each “line” in the dot structure represents 2 electrons.

Subtracting 2 from the total for each line drawn: 8 – 6 = 2 remaining.

N is in group 5A, so it has 5 valence electrons.

H is in group 1A so it has 1 valence electron

The compound NH3 has1 N and 3 Hs, so 5 + (3 x 1) gives a total of 8 valence electrons for the whole compound.

Check for happiness!

You try…

HF

H2O

F2

Double and Triple Bonds

DOUBLE and TRIPLE bonds are formed when atoms share 2 or 3 pairs of electrons to attain a stable, noble gas configuration.

These bonds are represented with multiple lines in a dot diagram.

EXAMPLE: Nitrogen molecule, N2

1. Count the total number of valence electrons, 5 for each nitrogen atom giving a total of 10.

2. Draw the atoms connected with a line. N N

3. Then, subtract 2 for each bond (line). 10 – 2 = 8 remaining. Place the 8 remaining electrons in pairs around the 2 nitrogens.

4. But, the Ns aren’t happy. They only have 6 electrons each. What can we do??

N N

N

Multiple Bonds Needed!

We can share more than one pair.

N N

Now each N has 8 electrons and is happy.

N

Let’s try a couple together…

CO2

C2H2

Coordinate Covalent Bonds

Formed when one atom contributes both bonding electrons so that each atom can achieve a noble gas configuration.

To represent this type of bond, we use an arrow going FROM the donor TO the atom who is receiving the electrons.

O donates a full pair of electrons for sharing, forming a COORDINATE COVALENT BOND and allowing each atom to achieve noble gas configuration.

Notice the arrow going from the O to the C.

C O

Coordinate Covalent Bonds

Let’s look at the compound carbon monoxide.

Resonance Structures

Structures that occur when it is possible to write 2 or more valid electron dot structures that have the same # of electron pairs for a molecule or an ion.

Example: O3, Ozone

OO O

O OO

Let’s try one together…

NO2-

The structures of ions are enclosed in brackets with the charge written on the outside.

Negative ions add electrons to the total count; positive ions take away electrons.

Stop for today.

Chemistry Joke

Q: What happened to the chemist who was reading a book about helium?

A: He just couldn’t put it down!