chemistry bonding

ions

-ions are charged particles, they can be single atoms or groups of atoms

-atoms lose or gain electrons to form a full outer shell and become an ion

-metals always lose electrons to form positive ions

-non metals always gain electrons to form negative ions

-oppositely charged ions are strongly attracted by electrostatic forces

-elements in the same group have the same amount of outer electrons so they form ions with the same charge

-mg= 2,8,2     cl= 2,8,7    mg->2 cl= mgcl2   

ionic compounds

- an ionic compound is a compound that only contains ionic bonds

- ionic compounds have a structure called a giant ionic lattice

-the ions form a closely packed regular lattice arrangement and there are very strong electrostatic forces of attraction between oppositely charged ions in all directions in the lattice

-a single crystal of sodium chloride is one giant ionic lattice and is regulary shaped

-ionic compounds all have high melting points and boiling points due to the many strong bonds

-they cant conduct electricity when solid, but can when melted or dissolved in water

covalent bonding

-when non metal atoms bond together they share pairs of electrons to make covalent bonds

-the positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons via electrostatic forces, making covalent bonds very strong

-covalent bonding can happen in compounds of non mentals and in non metal elements

-substances cointaining covalent bonds usually have simple molecular structures

- the atoms within the molecules are held together by very strong covalent bonds, by contrast the atoms between these molecules are very weak, so they are easy to melt and boil

-most molecular substances are gas or liquids @rt

-molecular compounds dont conduct electricity because there arent any free electrons or ions.

giant covalent structures

-all atoms are bonded to each other by strong covalent bonds

-very high melting and boiling points and lots of energy is needed to break them

-dont contain charged particles so dont conduct electricity (only graphite)

diamond- each carbon atom forms four covalent bonds in a very rigid structure

graphite-each carbon atom forms three covalent bonds to create layers of hexagons, each atom has 1 free electron

silicon dioxide- sometimes called silica, this is what sand is made of, each grain of sand is one giant structure of silicon and oxygen

allotropes of carbon

-allotropes are different structural forms of the same element in the same physical state

diamond- each atom forms four covalent bonds making it very hard, high melting point, no free electrons so doesnt conduct electricity.

graphite- each atom forms three covalent bonds between the layers which are held together very weakly so graphite is soft and slippery. has a high melting point- covalent bonds need alot of energy to break. only three of carbons four outer electrons are used in bonds, so each carbon atom has one delocalised electron that can conduct electricity.

graphene- graphene is a sheet of carbon atoms held together in hexagons.the sheet is just one atom thick and is very strong and light so can be added to ther materials to improve their strength without adding too much weight. like graphite, contains delocalised electrons so can conduct electricity through the whole structure and has the potential to be used in electronics.

fullerenes

-fullerenes are molecules of carbon shaped like closed tubes or hollow balls

-made up of carbon atoms arranged in hexagons, pentagons and heptagons

-buckminsterfullerene was the first fullerene to be discovered, has the formula c60 and forms a hollow sphere of 20 hexagons and 12 pentagons

-fullerenes can be used to cage other molecules. the fullerene structure forms around another atom or molecule and traps it inside. this can be used to deliver a drug into the body

-fullerenes have a huge surface area so could help make great industrial catalysts

nanotubes- fullerenes can form nanotubes-tiny carbon cyclinders- the length-diameter ratio is very high. conducts electricity and heat. they have tensile strength so they dont break when stretched. technology that uses very small particles such as nanotubes is called nanotechnology.

metallic bonding

-metals consist of a giant structure

-the outer shell electrons of metal atoms are free and there are strong electrostatic attractions between the positive metal ions and the shared negative electrons. these forces of attraction hold the atoms together in a regular structure and are known as metallic bonding which is very stong

-very high melting and boiling point so are generally solid @rt

- the free electrons carry electrical current and thermal energy throughout the structure

-the layers of atoms in metals can slide over each other making metals malleable so they can be shaped.

-alloys are a mixture of a metal and another element and have distorted layers due to atoms being differnt sizes, making them harder to slide over each other which makes them harder

nanoparticles

-nanoparticles have a diameter between 1nm (1 x 10-9m) and 100nm (1 x 10-7m) and contain only a few hundred atoms

-they have huge s.a-volume ratio

-absorbed easier by the body than most particles so could be used to deliver drugs into the correct cells

- some conduct electricity so can be used in tiny electric circuits for computer chips

-silver nanoparticles have antibacterial properties

-used in cosmetics-eg used to improve moisturisers  without making them oily

-there isnt much research on them at the moment so alot of people dont trust them.