Molecular Compounds (a.k.a. Covalent Compounds)

Ionic Compounds Review

• Ionic compounds are the combination of ions. E.g. Na+ + Cl- NaCl.

• This formula represents the __________ of sodium ions and chloride ions not the exact number of them.

• They are composed of a ___________________ and form a crystal structure (e.g. NaCl and CaCl2 which are both salts)

Molecular Compounds

• Consist of atoms covalently bonded together

• The elements involved are all __________

Some examples

• N2O _____________ = Gas used at the dentist to relax patients

• NO2 _____________ = poisonous toxin emitted from car exhaust

More Examples

• H2O ______

• CO2 ____________ = Gas

exhaled and created during combustion reactions• CO ____________________= Lethal

gas created during incomplete combustion

Recall

• In ionic compounds, the non-metal rips away the electron(s) from the metal because the metals loosely hold their electrons

• This creates a positive and negative ion which attract each other making them stick together (opposites attract)

Molecular Compounds• made up of a non-metal and a non-metal.

• also called _____________

Molecular Compounds• ________ electrons (e-) to

form a ________________.

• Neg. e- are attracted to the Pos. nuclei of both atoms

Molecular CompoundsMolecular compounds are formed

when non metals share electrons to fill their outer electron orbit (shell).

If we draw the Lewis Structure for Fluorine,

We can see that it needs ________

It wants to share one electron with another atom.

If it bonds with another fluorine atomWe draw the shared pair of

electrons between the two atoms.

F F

F F

Shared electron pair ______

Molecular CompoundsMany molecular compounds are

predictable. How will Oxygen bond with

Hydrogen to form a molecule.Draw the Lewis Structure of both

Atoms.________________________

Clearly we need another Hydrogen atom

Putting the shared electrons between the atoms.

The molecule is H2O

H OH

H O

H

**The Oxygen atom has 8 valence electrons (full) and the Hydrogen has 2 valence electrons (full)

Molecular CompoundsNot all molecular compounds are as

predictable.How will Oxygen bond with Carbon?Draw the Lewis Structures of each

atom. ___________________________

If we add one more Oxygen, each oxygen can share two.

However, if Oxygen will share two and donate one of its other electrons pairs, Oxygen can bond with just on Carbon atom.

OC

OCO

C O

_____________

_____________

Types of Bonds

OCO

Carbon Monoxide – Triple Bond because _______pairs of electrons are shared

H O

H

Water – Single bond because ______ pair of electrons are shared

Carbon Dioxide – Double bond because _______pairs of electrons are shared

C O

Molecular Compounds – Naming

So Oxygen can form CO or CO2

We need a more flexible naming system for covalent compounds to reflect the many different bonding possibilities.

To name a covalent compound,1. Starting with the atom that is

to the left in the periodic table, (or lower)

2. Write the name of the atoms with the prefix indicating the number of that atom in the compound.

3. Change the ending of the last atom to – ide.

The prefixes are,1 _______2 _______ 3 _______4 _______5 _______6 _______7 _______

Note, the mono is omitted on the first atom.

CO _____________

CO2 _____________

Memorize me!

Number Prefix Number Prefix

1 mono 6 _________

2 _________ 7 hepta

3 tri 8 _________

4 _________ 9 nona

5 penta 10 _________

Naming Example

• P4O10

Phosphorus - use prefix tetra (4)Oxygen – change ending – OxideOxide – use prefix deca (10)

= _________

Molecular Compounds - NamingName the following compounds

CF4

_________

H2O

_________

PF5

_________

Write the chemical formula for,

Sulphur Dioxide

_________

DiCarbon Tetrahydride

_________

Molecular Compounds – Diatomic Gases

Molecular compounds show an incredible variety in structure, physical and chemical properties.

There are categories that further divide covalent compounds into categories with common properties.

Diatomic Gases – _________

The Halogens, Oxygen, Nitrogen and Hydrogen form diatomic gases.

H2 is called Hydrogen Gas not Dihydrogen.

Eg. N2 - _________

O2 - _________

Air

Writing Formulas

left-most element goes 1st

Carbon monoxide

- Carbon (C) no prefix therefore = C- Monoxide – Mono = 1 therefore, 1 oxygen

atom = O= _________

Writing Formulas

• Nitrogen dioxide

- Nitrogen (N) no prefix therefore = N- Dioxide – Di = 2 therefore, 2 oxygen

atoms = O2

= _________

Writing Formulas

DiCarbon Tetrahydride

- Dicarbon (C) Di = 2 therefore = C2

- Tetrahydride (H) Tetra = 4 therefore, 4 Hydrogen atoms = H4

= _________

Exceptions that need to be Memorized!

CH4 – _________

H2O2 – _________

H2O – Water

These Too!

NH3 – _________

O3 – _________