Ionic Compounds Review
• Ionic compounds are the combination of ions. E.g. Na+ + Cl- NaCl.
• This formula represents the Ratio of sodium ions and chloride ions not the exact number of them.
• They are composed of a Metal and a Non-Metal 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 Non-Metals
Some examples
• N2O Nitrous Oxide= Gas used at the dentist to relax patients
• NO2 Nitrogen Dioxide= poisonous toxin emitted from car exhaust
More Examples
• H2O Water
• CO2 Carbon Dioxide= Gas
exhaled and created during
combustion reactions
• CO Carbon Monoxide= 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 Covalent Compounds
Molecular Compounds
• Share electrons (e-) to form a stable arrangement.
• 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 one more electron to become stable
It wants to share one electron with another atom.
If it bonds with another fluorine atom
We draw the shared pair of electrons between the two atoms.
F F
F F
Shared electron pair both now have 8 electrons in outer orbit.
Molecular CompoundsMany molecular compounds are
predictable. How will Oxygen bond with
Hydrogen to form a molecule.Draw the Lewis Structure of both
Atoms.Oxygen wants to share two
electrons and hydrogen wants to share one.
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. Carbon wants to share 4.Oxygen wants to share 2
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
Carbon Dioxide
Carbon Monoxide
Types of Bonds
OCO
Carbon Monoxide – Triple Bond because three pairs of electrons are shared
H O
H
Water – Single bond because One pair of electrons are shared
Carbon Dioxide – Double bond because two pairs of electrons are shared
C O
Molecular Compounds – NamingSo 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 Mono
2 Di
3 Tri
4 Tetra
5 Penta
6 Hexa
7 Hepta
Note, the mono is omitted on the first atom.
CO Carbon Monoxide
CO2 Carbon Dioxide
Memorize me!
Number Prefix Number Prefix
1 mono 6 Hexa
2 Di 7 hepta
3 tri 8 octa
4 Tetra 9 nona
5 penta 10 deca
Naming Example
• P4O10
Phosphorus - use prefix tetra (4)
Oxygen – change ending – Oxide
Oxide – use prefix deca (10)
= Tetraphosphorus Decaoxide
Molecular Compounds - Naming
Name the following compounds
CF4
Carbon tetrafluoride
H2O
Dihydrogen Monoxide
PF5
Phosphorus Pentafluoride
Write the chemical formula for,
Sulphur Dioxide
SO2
DiCarbon Tetrahydride
C2H4
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 – When two atoms of the same type form a covalent molecule, the result is often a colorless, odorless gas.
The Halogens, Oxygen, Nitrogen and Hydrogen form diatomic gases.
H2 is called Hydrogen Gas not Dihydrogen.
Writing Formulas
left-most element goes 1st
Carbon monoxide
- Carbon (C) no prefix therefore = C- Monoxide – Mono = 1 therefore, 1 oxygen
atom = O= CO
Writing Formulas
• Nitrogen dioxide
- Nitrogen (N) no prefix therefore = N
- Dioxide – Di = 2 therefore, 2 oxygen atoms = O2
= NO2
Writing Formulas
DiCarbon Tetrahydride
- Dicarbon (C) Di = 2 therefore = C2
- Tetrahydride (H) Tetra = 4 therefore, 4 Hydrogen atoms = H4
= C2H4