Covalent Bonding

Vocabulary• covalent

bond• single bond• double bond• triple bond• molecule• structural

formula“Dancer”, Fernando Botero

Columbian, 1982

Review

What is an ionic bond?

What if?

If an ionic bond requires one atom to lose electrons and one atom to gain electrons, how could two atoms bond if both atoms do not want to lose electrons but still must follow the octet rule?

What if?

Let’s look at an example: chlorine gas, Cl2

How many electrons does each chlorine atom need to gain to havea full octet?

Cl Cl

What if?

Because neither chlorine atom is willing to to give up an electron, they can not form an ionic bond. Instead each atom can SHARE one electron with the other atom to fulfill the octet rule for each.

Cl Cl

What if?

Because neither chlorine atom is willing to to give up an electron, they can not form an ionic bond. Instead each atom can SHARE one electron with the other atom to fulfill the octet rule for each.

Cl Cl

What if?

Because neither chlorine atom is willing to to give up an electron, they can not form an ionic bond. Instead each atom can SHARE one electron with the other atom to fulfill the octet rule for each.

Cl Cl

What if?

Notice that by sharing, each atom now has 8 valence electrons around it and follows the octet rule: the 7 it originally had and 1 from the other atom.

Cl Cl

Covalent Bonding

This sharing of electrons is called a covalent bond. Because only one electron is being shared from each atom in this example, it is called a single covalent bond.

Cl Cl This is the Lewis structure for the Cl2 molecule.

When atoms bond covalently, they form molecules.

Covalent Bonding

Let’s look at another molecule, O2. Draw the

Lewis structures for the two oxygen atoms separately.

O OHow do you think these two atoms can bond?How many electrons does each atom need to gain or share to achieve an octet?

Covalent Bonding

Let’s look at another molecule, O2. Draw the

Lewis structures for the two oxygen atoms separately.

O OHow do you think these two atoms can bond?How many electrons does each atom need to achieve an octet?

Covalent Bonding

Let’s look at another molecule, O2. Draw the

Lewis structures for the two oxygen atoms separately.

O OHow do you think these two atoms can bond?How many electrons does each atom need to achieve an octet?

Covalent Bonding

Let’s look at another molecule, O2. Draw the

Lewis structures for the two oxygen atoms separately.

O OHow do you think these two atoms can bond?How many electrons does each atom need to achieve an octet?

Covalent Bonding

Look at each atom now. Each atom is sharing two electrons with the other atom and now each has 8 valence electrons.

O OThis is the Lewis structure for

the O2 molecule.Because each atom is sharing 2 valence electrons, this is called

a double covalent bond.

Covalent Bonding

Look at each atom now. Each atom is sharing two electrons with the other atom and now each has 8 valence electrons.

O OWe can also draw it this way. This is called the structural

formula for O2. Each line represents two electrons.

Covalent Bonding

Important covalent bonding notes:• sharing of electrons to achieve an octet

(hydrogen is a notable exception because it only needs two valance electrons)• occur between non-metal atoms• can be single, double, or triple bond

Practice

a) NaClb) H2O

c) Li3P

d) CO2

e) C6H12O6

f) SrBr2

g) Al2O3

h) PCl5

Which of the following compounds will have covalent bonds?

Practice

Draw the Lewis structure for water. Are the bonds single, double, or triple covalent bonds.

HH

OSteps1) Draw each atom’s

Lewis structure.2) Pair up unpaired

electrons.

Practice

Draw the Lewis structure for water. Are the bonds single, double, or triple covalent bonds.

HH

OSteps1) Draw each atom’s

Lewis structure.2) Pair up unpaired

electrons.3) Rearrange atoms

so that electron pairs are connected.

Practice

Draw the Lewis structure for water. Are the bonds single, double, or triple covalent bonds.

Steps1) Draw each atom’s

Lewis structure.2) Pair up unpaired

electrons.3) Rearrange atoms

so that electron pairs are connected.

HH

O

Practice

Draw the Lewis structure for water. Are the bonds single, double, or triple covalent bonds.

There are two single covalent bonds in a water molecule.

HH

O

Practice

Draw the Lewis structure for PCl3.

Steps1) Draw each atom’s

Lewis structure.2) Pair up unpaired

electrons.3) Rearrange atoms so

that electron pairs are connected.

PCl ClCl

Practice

Draw the Lewis structure for HCN.

Steps1) Draw each atom’s

Lewis structure.2) Pair up unpaired

electrons.3) Rearrange atoms so

that electron pairs are connected.

CH NSingle bond

Triple bond