Covalent Bonding

Forming Molecular Bonds

What is a covalent bond?

The chemical bond that results from the sharing of electrons Non-metals combine to acquire a full valence

shell of 8 valence electrons Example:

7 valence e- 8 valence e-

Degree of sharing

Non-polar Covalent

Polar Covalent

Ionic

e- are shared equally

e- shared unequally

one atom takes e-

from another

Na

Cle-

Types of covalent bonds

Single Covalent bonds- (also called sigma bonds) When a single pair of electrons is shared Ex: H H

Group 7A: will form single covalent bonds Group 6A: will form two single covalent bonds Ex: H2O

Group 5A: will form three single covalent bonds Ex: NH3-

Ammonia Group 4A: will form four single covalent bonds Ex: CH4

- methane

Types of covalent bonds continued…

Multiple covalent bonds: Double or Triple bonds

Double covalent bond- when two pairs of electrons are shared. Ex: O2 (draw lewis structure)

Triple covalent bond- formed when three pairs of electrons are shared between two atoms. Ex: N2 shares three pairs of electrons.

Pi bonds π- multiple bond consists of one sigma and one pi bond.

triple bond- one sigma and two pi bonds.

The shorter the bond the stronger the bond. Triple bonds are shorter.

Lewis dot structuresRules for drawing dot structures:

1. Calculate the number of valence e- each atom contributes. Divide this number in half to get the number of pairs.

:::: :

:

ex: CBr4 C = 4

Br = 7 x 4 = 28

32 e-

16 prs

3. Use pairs of e- (as single covalent bonds) to attach all the other atoms to the center atom.

ex: CBr4

C Br

Br

Br

Br

4. Put lone pairs of e- on the outside atoms until each atom has 8 electrons (4 pairs) or 1 pair on hydrogen.

5. Put any leftover pairs on the center atom so that it also has 4 prs around it.

:

:

:

:

:

:

:

:

: :

:

:

Lewis dot structures continued…

2. Decide which element will be the center at usually the one that has fewer atoms or the lower electronegativity

CH4 SO2 PCl5

Lewis dot structures continued…

CH4

What is the central atom?

C

How many valence electrons does it have? 4How many hydrogens are there? 4 How many valence electrons do each have? 1

H

H

H

H

Now, join the electrons with a bond

How many sigma bonds are there?

4

diatomic elements

H2 O2 Br2 F2 I2 N2 Cl2

Octet Rule:

atoms share electrons in order to have 8 valence e- (2 for hydrogen)

Naming Covalent Compounds

Covalent compounds are named by adding prefixes to the element names.

‘Covalent’ means both elements are nonmetals.

A prefix is added to the name of the first element in the formula ONLY if more than one atom of it is present.

A prefix is ALWAYS added to the name of the second element in the formula

The second element will use the form of its name ending in ‘ide’.

Naming Covalent CompoundsPrefixes

Subscript Prefix

1 mono-

2 di-

3 tri-

4 tetra-

5 penta-

Subscript Prefix

6 hexa-

7 hepta-

8 octa-

9 nona-

10 deca-

Note: When a prefix ending in ‘o’ or ‘a’ is added to ‘oxide’, the final vowel in the prefix is dropped.

Naming Binary Covalent Compounds: Examples

N2S4dinitrogen tetrasulfide

NI3 nitrogen triiodide

XeF6 xenon hexafluoride

CCl4 carbon tetrachloride

P2O5 diphosphorus pentoxide

SO3 sulfur trioxide

1 mono

2 di

3 tri

4 tetra

5 penta

6 hexa

7 hepta

8 octa

9 nona

10 deca

* Second element ends ‘ide’

* Drop –a & -o before ‘oxide’

Writing Chemical Formulas: A Review

I. Ionic Compounds

II. Covalent Compounds

Writing Formulas for Covalent Compounds

The names of covalent compounds contain prefixes that indicate the number

of atoms of each element present.

Remember: Binary compounds contain only two elements, both of which are nonmetals When in covalent compounds

atoms DO NOT have chargesSubscripts are determined directly from the prefixes in the

name.

• First element:• if there is only one atom of that element in the formula (its subscript will be

1) and there should NOT be a prefix

• Second element: • will ALWAYS have a prefix• will ALWAYS end in -ide

Writing Formulas for Binary Covalent

Compounds: Examplesnitrogen dioxide NO2

diphosphorus pentoxide P2O5

xenon tetrafluoride XeF4

sulfur hexafluoride SF6

1 mono

2 di

3 tri

4 tetra

5 penta

6 hexa

7 hepta

8 octa

9 nona

10 deca

* Second element ends in ‘ide

* Drop –a & -o before ‘oxide’

Writing Formulas: Practice

carbon tetrafluoride CF4

Na3PO4sodium phosphate

Cu2SO4copper (I) sulfate

Analysis If “Yes”

The compound is covalent: the

prefixes give the subscripts.

* Are there prefixes present

The compound is ionic:

subscripts must be

determined by balancing

charges

prefixes covalent prefixes indicate subscripts

metal ionic balance charges 3 Na1+ needed for 1 PO43-

metal present ionic balance charges 2 Cu1+ needed for 1 SO42-

Al2S3aluminum sulfidemetal present ionic balance charges 2 Al3+ needed for 3 S2-

N2O5dinitrogen pentoxideprefixes covalent prefixes indicate subscripts

NH4NO3ammonium nitratepolyatomic ion present ionic balance charges

1 NH41+ needed for 1 NO3

1-

PbO2lead (IV) oxidemetal present ionic balance charges 1 Pb4+ needed for 2 O2-

Fe2(CO3)3 iron (III) carbonatemetal present ionic balance charges 2 Fe3+ needed for 3 CO3

2-