1. 5.2 sheet a Bonding, structure and properties
Covalent Bonds
Form when non-metals share electrons between them.
Attraction between each atom and the shared electron pair.
Atoms share electrons to complete their outer shells
One bond is formed for each electron that was needed.
Bonding represented with dot-and-cross diagrams showing only the outer-shell electrons.
Forming Ions
Cations are positive (cat…pussitive!) ions
They are formed when atoms lose electrons.
Metals form cations by losing the electrons in their outer shells
In the example, aluminium loses its three outer-shell electrons to become Al3+…each lost electrons cause 1 ‘+’ charge.
Anions are negative ions
They are formed when atoms gain electrons.
Non-metals form anions by filling their outer shells.
Name ends with ‘-ide’ to show it is a negative ion,
In the example, oxygen gains two outer-shell electrons to become O2-, giving it 8 electrons in its outer shell. 3+
Making Ionic Compounds
An ionic bond is the attraction between a positive and a negative ion.
The overall number of positive and negative charges must cancel out.
Ionic bonds form between a metal and a non-metal
Ionic compounds do not form molecules
Example 1: Magnesium reacting with chlorine.
Anion: Cl forms Cl- ions
Cation: Mg forms Mg2+ ions
Formula = MgCl2
Why: two Cl- gives a 2- charge to balance 2+ from Mg2+.
Name: magnesium chloride
Example 2: aluminium reacting with oxygen.
Anion: O forms O2- ions
Cation: Al forms Al3+ ions
Formula = Al2O3
Why: Two Al3+ gives a 6+ charge, three O2- gives a 6- charge.
Name: aluminium oxide
Example 1: Water
Each hydrogen needs one more electron to complete it’s outer shell and the oxygen needs two more. Oxygen forms two single bonds: one to each hydrogen.
Example 2: Carbon dioxide
Carbon needs two more electrons to complete it’s outer shell and each oxygen needs two more. Carbon forms two double bonds: one to each oxygen. H O O C
Covalent structures
Simple Covalent Molecules
Molecule = A particle made of a small group of atoms, covalently bonded together.
Low melting and boiling point, due to weak attractive forces between molecules..
Electrical insulator as no electrons free to move.
Examples: water, ammonia, oxygen
5.2 sheet a Bonding, structure and properties
Ionic Structures
A repeating 3D lattice of positive and negative ions.
Strong electrostatic bonds between ions.
Diamond vs Graphite
These are two examples of giant covalent compounds.
They are carbon allotropes.
Displayed formulas
This format shows the covalent bonds as lines.
Double bonds are shown as two parallel lines.
Properties of Ionic Compounds
Melting point: High due to strong bonds between ions.
Boiling point: Higher, due to strong bond between ions.
Solid: do not conduct electricity
Molten (liquid): do conduct electricity
Dissolved (aqueous): do conduct electricity
Why?
Electrical Conductivity
Electricity is conducted when there are charged particles that are free to move.
Solid: there are charged particles (the ions), but they are not free to move, so they do not conduct.
Liquid/Aqueous: the ions are now free to move, so they do conduct
High Melting/Boiling Points
Ionic bonds (attraction between positive and negative ions) are very strong.
Melting and boiling require these bonds to be broken.
This takes lots of (heat) energy.
Diamond:
Very hard, as all carbon atoms joined with 4 strong covalent bonds.
Used to make cutting tools
Insulator as all electrons locked-tight in bonds, so can’t move.
Graphite:
3 covalent bonds per carbon atom
Layers of hexagonal carbon mesh that rub away from each other, as there are only weak forces between the layers.
Used as a lubricant.
Conductor as the electrons between the layers are free to move. This is very rare for a giant covalent structure.
Metallic Bonding
For alloys, see sheet 5.10a
Electrons are delocalised, moving freely between all the atoms creating a ‘sea of electrons’
All atoms have a positive charge as their outer-shell electrons have left them.
The bond is the attraction between the positive ions and the sea of electrons.
Conduct electricity as electrons are free to move.
Malleable (change shape but don’t shatter when hit) because rows of atoms slide past each other when hit

2. 5.2 sheet b Types of matter States of matter State symbols Solids Gas
Material comes in three different forms – solid, liquid and gas. These are the three states of matter.
Which state a material is in depends on how strong the force of attraction is between the particles (atoms, ions or molecules).
The strength of the force is determined by:
The material
The temperature
The pressure
We show these states of matter in particle diagrams (see the diagram below).
State symbols
Solid - s
Liquid – l
Gas – g
Aqueous - aq
Solids
Strong forces of attraction
Regular lattice arrangement
Keep a definite shape and volume
Do not flow like liquids
Particles vibrate around their fixed positions.
Vibrate more when the temperature increases. This causes the solid to expand slightly.
5.2 sheet b Types of matter
Gas
Force of attraction between the particles is very weak
Particles are free to move constantly with a random motion
Particles travel in straight lines until they collide with other particles or walls
Particles far apart
Most gas is empty space
Don’t keep a definite shape or volume
Will fill any container
The hotter a gas gets, the faster the particles will move. The more the particles move, the more they collide with each other and the container. This causes the pressure to increase or, if the container isn’t sealed, the volume to increase.
Liquids
Weak forces of attraction between the particles
The particles are randomly arranged and are free to move past each other
Particle tend to stick closely together but move around
Have a definite volume
Do not keep a definite shape
Will flow to fill the bottom of a container
Nanoparticles
These are tiny particles often measured in nanometres (nm) or micrometres (μm).
Particles are put into three categories depending on their diameter:
Coarse particles – diameters between 250nm and 10,000nm. Also referred to as dust or PM10 (Particulate matter up to 10 micrometres in diameter).
Fine particles – diameters between 100nm and 2500nm. Also known as PM2.5.
Nanoparticles – diameters between 1nm and 100nm. Nanoparticles contain only a few hundred atoms.
Nanoparticles have a huge surface area to volume ratio.
Surface area to volume ration can be calculated using the following:
Surface areas to volume ratio = surface area  ÷ volume
Nanoscience (the study of nanoparticles) may lead to the development of:
new catalysts
new coatings
new computers
stronger and lighter building materials
sensors that detect individual substances in tiny amounts.
Changes of state