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SIMPLE COVALENT COMPOUND PROPERTIES
Noadswood Science, 2012
Wednesday, April 19, 2023
To understand the properties of simple covalent compounds
Covalent Bonding – Recap
A covalent bond forms when two non-metal atoms share a pair of electrons: the electrons involved are in the highest occupied energy levels (outer shells) of the atoms
An atom that shares one or more of its electrons will complete its highest occupied energy level
Covalent bonds are strong – a lot of energy is needed to break them
Substances with covalent bonds often form molecules with low melting and boiling points, such as hydrogen and water
Covalent Bonding – Recap
HH
HH
Incomplete outer shells
Both atoms have a full outer shell
When non-metal atoms react together, they need to gain electrons to fill their outer shell and become stable
They can only do this if they share electrons with each other – they are covalently bonded
Example Compounds
Hydrogen atoms can each form one covalent
bond, while oxygen atoms can each form two
covalent bonds
Two pairs of electrons are shared in a water molecule (H2O)
Hydrogen atoms and chlorine atoms can each form one
covalent bond
One pair of electrons is shared in a hydrogen chloride molecule
(HCl)
Hydrogen atoms can each form one covalent bond, while and nitrogen
atoms can each form three covalent bonds
Three pairs of electrons are shared in an
ammonia molecule (NH3)
Covalent Compounds
Covalent bonds form between non-metal atoms
Each bond consists of a shared pair of electrons and is very strong – covalently bonded substances fall into two main types: -
Simple molecules
Giant covalent structures
Simple Molecules
These contain only a few atoms held together by strong covalent bonds
An example is carbon dioxide (CO2), the molecules of which contain one atom of carbon bonded with two atoms of oxygen
How would you draw out carbon dioxide?
Simple Molecules
Atoms that join together by covalent bonding can form different types of covalent structure
Oxygen, water and carbon dioxide are molecules – they have a simple structure because they only contain a few atoms
Draw out the above simple molecules…
OO COOH
O
H
Oxygen Water Carbon dioxide
Simple Molecules – Iodine
Most molecular substances are gas or liquid at room temperature
A few are solid and these are called molecular solids, e.g. iodine…
Iodine is a molecular solid at room temperature – two iodine atoms form a single covalent bond to become an iodine molecule
Millions of iodine molecules are held together by weak forces of attraction to create a 3D molecular lattice
Weak forces of attraction
Simple Properties
Simple molecular substances have the following properties: -
Low melting and boiling points – this is because the weak intermolecular forces break down easily
Non-conductive – substances with a simple molecular structure do not conduct electricity because they do not have any free electrons or an overall electric charge
Solids are usually soft and brittle, shattering when hit, and insoluble in water (but soluble in other solvents, e.g. petrol)
Simple molecular substances are gases, liquids or solids with low melting and boiling points
Intermolecular Forces
Hydrogen, ammonia, methane and water are also simple molecules with covalent bonds
All have very strong bonds between the atoms, but much weaker forces holding the molecules together – when one of these substances melts or boils, it is these weak 'intermolecular forces' that break, not the strong covalent bonds