Topic 2 - bonding, structure and properties of matter Flashcards
Ions
Charged particles
When atoms lose or gain electrons to form ions they are just trying to get a full outer shell to be stable
When electrons are lost the become positive ions
When electrons are gained they become negative ions
The number of electrons gained or lost is the same as the charge on the ion
Diagrams which show how ionic bonds are formed
Dot and cross diagram
Ionic compounds structure
- giant ionic lattice
- very strong electrostatic forces of attraction between oppositely charged ions as they are closely packed
Ionic compounds properties
- all have high mp and bp due to the many strong bonds between the ions. Takes lots of energy to overcome this attraction
- when they’re solid the ions are held in place, so the compounds cant conduct electricity
- when ionic compounds melt, the ions are free to move and they’ll carry electric current
- dissolve easily in water. The ions separate and are all free to move in the solution so they’ll carry an electric current
Ionic bonding is between
A non metal and a metal
Covalent bonding is between
Two non metals
Why covalent bonds are very strong
The positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces
Different ways of drawing covalent bonds
Dot and cross diagrams
Displayed formula
Polymers
Lots of small units are linked together to form a long molecule that has repeating sections.
All atoms ina polymer are joined by strong covalent bonds
Intermolecular forces of polymers
Larger than between simple covalent molecules, so more energy is needed to break them.
Still weaker than ionic or covalent, so generally have lower boiling points than ionic of giant molecular compounds
Giant covalent structures
All atoms are bonded to each other by strong covalent bonds
Have very high melting and boiling points as lots of energy is needed to break the covalent bonds between the atoms
Don’t contain charged particles, so don’t conduct electricity
Diamond
Giant covalent structure
Made up of carbon atoms that each form four covalent bonds-making diamond very hard
Strong covalent bonds take a lot of energy to break giving it a very high mp
Doesn’t conduct electricity as it has no free electrons or ions
Graphite
Each carbon atom only forms three covalent bonds creating sheets of carbon atoms arranged in hexagons
Aren’t any covalent bonds between the layers - they’re only held together weakly so they’re free to move over each other - making it soft and slippery (ideal for a lubricant)
Has a high mp- covalent bonds in they layers need lots of energy to break
Only 3/4 of carbons outer electrons are used in bonds, so each carbon atom has one delocalised electron- so graphite conducts electricity and heat
Graphene
A sheet of carbon atoms joined together in hexagons
Sheet is one atom thick making it a 2D compound
Network of covalent bonds makes it very strong
It is very light and can be added to composite materials to improve their strength without adding much weight
Contains delocalised electrons so can conduct electricity through the whole structure- potential to be used in electronics
Fullerenes
Molecules of carbon shaped like closed tubes or hollow balls
Mainly made up of carbon atoms in hexagons
Can be used to ‘cage’ other molecules. The structure forms around another atom or molecule which is then trapped inside which could help to deliver a drug into the body
Huge surface area - could help make great industrial catalysts
Make good lubricants
Metallic bonding is between
Two metals
Why metallic bonding is very strong
Strong forces of electrostatic attraction between the positive metal ions and the shared negative electrons hold the atoms together in a regular structure
Why most metals are solid at room temperature
The electrostatic forces between the metal atoms and the delocalised sea of electrons are very strong, so need lots of energy to be broken - giving most compounds with metallic bonding high mp and bp
Why metals are good conductors
The delocalised electrons carry electrical current and thermal energy through the whole structure so metals are good conductors of heat and electricity
Why metals are malleable
The layers of atoms in a metal can slide over each other easily
Why alloys are harder than pure metals
Different elements have different sized atoms which means the layers cant slide over each other as easily unlike pure metals
Solids
1) strong forces of attraction between particles, which holds them close together in fixed positions to form a very regular lattice arrangement
2) particles don’t move from their positions,so all solids keep a definite shape and volume and don’t flow like liquids
3) particles vibrate about their positions - the hotter the solid is the more it vibrates (causing it to expand slightly)
Liquids
1) weak force of attraction between the particles
2) they’re randomly arranged and free to move past each other but they tend to stick closely together
3) have a definite volume but don’t keep a definite shape and will flow to fill the bottom of a container
4) particles constantly move with random motion
5) hotter the liquid gets, the faster they move, causing liquids to expand slightly when heated
Gases
1) Very weak forces of attraction between particles
2) free to move and are far apart and travel in straight lines
3) don’t keep a definite volume or shape and will always fill any container
4) particles move constantly with random motion - the hotter the gas gets the faster they move
5) gases either expand when heated or their pressure increases
