Chemistry topic 2 IGCSE revision

what are ionic compound held together by

strong electrostatic forces

what are ionic compounds found as

regular lattic crystals

why do ionic compounds have high boiling/melting points

• Strong electrostatic forces

• requires lots of energy to break

• high temperature required

when do ionic compounds conduct electricity and why?

• when molten

• because ions are free to move

• can carry a charge

general idea for why some diagrams may not be effective in displaying an ionic compound

it is not to scale

it gives no information about the forces of attraction between the ions

it gives no information about the movement of electrons to form the ions

what defines a simple covalent molecule

2 or more atoms joined together by shared electrons in their valence shield

why do simple covalent structures have low boiling/melting points

• weak intermolecular forces

• easily with little energy broken apart

• so often gas/liquid

why do simple covalent molecules not conduct electrity

They lack any delocalised electrons

They are not ions because they share rather than give electrons away

what are simple covalent molecules held by

weak intermolecular forces

what are giant covalent molecules defined as

covalently bonded non metals which have a large network of many covalent bonds

when do giant covalent molecules conduct electricty

• when covalent bonds do not use an electron

• electron becomes delocalised

• able to carry a current

why do giant covalent molecules have high boiling/melting points

• Many and strong covalent bonds keep them together

• require a lot of energy to break apart

• thus high temperature required

what are metallic bonds defined as

a metal atom that is held together with other metal atoms that are positvely charged with negatively charged electrons with strong electromagnetic forces.

what makes metallic bonds able to conduct electricity

the sea of delocalised electrons are able to carry a current

what makes metallic bonds have very high boiling/melting points

very strong metallic bonds (electromagnetic forces) hold the metal together and take a lot of energy to seperate thus requiring high temperatures to break these bonds.

what are metallic bonds held by

strong metalic bonds (electromagnetic forces)

what is an alloy defined as

alloys are a mixture of a metal and either a metal or non metal

what makes alloys strong

• Alloys have lattice structures

• the differnet sizes elements distort the structure

• this makes it harder for the atoms to slide over eachother

how many covalent bonds are in graphite

3

how many covalent bonds are in diamond

4

why does graphite conduct electricty

single delocalised electron per 3 covalent bonds which carries a current

why is diamond so strong

• many and strong covalent bonds

• require lots of energy/force to break apart

why is graphite soft

made of layers of graphene which are held together by weak intermolecular forces which make them easy to slide over one another and thus make graphite soft

buckminsterfullerene uses

• Drug delivery systems

• Catalysts

• Lubricants

• Reinforcing materials

what is a nano particles defined as

• very smal structures

• between 1 - 100 nanometers

why can carbon nanotubes conduct electricity

• contain delocalised electrons

• electrons can carry charge throughout the structure

why buckmisterfullerene is used as a lubricant

molecules are spherical

so molecules will roll

why buckmisterfullerene is used as a drug delivery system

it is hollow

allow 'acts as a cage'

it is unreactive

it is not toxic

it has a large surface area to volume ratio

suggest why doctors opt for nanoparticles over coarse particles

• nanoparticles have a larger surface area to volume ratio

• So less can be used for the same effect

possible risks of using nanoparticles

• damages cells

• heart problems

• get into the bloodstream

• pass into cells

• catalysing harmful reactions

• harmful to aquatic life

why do nanoparticles work as catalyst

increase collisions due to increased surface area : volume