CHEMISTRY REVISION
what must happen for a chsnge in state
energy must be transferred via hesting
during changes in state particles gain energy which is used for
-break some of the bonds between particles durinh melting
-overcome the remaining forces of attrsction between particles during evaporating or boiling
plum pudding
a positively charged ball with negative electrons embedded in it
nuclear model
positively charged alpha particles were fired at thin gold foil. some went through the foil but others scattered in different directions.
in the nuclear model
-the mass of an atom is concentrated at its centre, the nucleus
-the nucleus is positively charged
relative masses of the particles
proton 1
electron very small
neutron 1
relative charge of the particles
proton +1
neutron 0
electron -1
atomic number
the number of protons in sn element
mass number
total smount of protons and neutrons
isotopes
atoms of the same element with different numbers of neutrond
ram
weighted average of the masses of the atoms of the isotopes.
ion
an ion is an atom or group of atoms with a positive or negative charge. ions form when atoms lose or gain electrons to obtsin a full outer shell
metal vs non metsl
metal atoms - lose electrons
non metal atoms- gain electrons
ionic compound
giant structure of ions in a regular repeating lattice structure of oppositely charged ions next to eachother
ionic bondibh
the ionic lattice is held together by strong electrostatic forces of attraction between the oppositely charged ions. the forced act in all directions in the lattice
properties if ionic compounds
-hmp
-hbp
-conduct when melted or in a solution
-solid at room temp
conservation of mass
no atoms are lost or made in a chemicsl reactio. instead the atoms join together in different ways to form products
relative formula mass
the relative mass of its atom compared to the mass of a carbon -12 atom
group 7
halogens :3
hslogens elements
H- very reactive yellow gas
Cl- less reactive green gass
Br- reddy brown , poisonous volatile liquid
I- dark grey solid
halogen reactivity
mp and bp increase as you go down the group
reactivity decreases as you go down the group
group 0
noble gasses
noble gases properties
-inert- full shells of electrons
-colourless gases
-bp increases as you go down the grouo
mixture
2 or more different substances, not chemically joined together
filtration
used to seperate an insoluble solid from a liquid
crystallisation
used to produce solif crystals from a solution. when the solution is warmed , some of the solvent evaporates leaving crystals behind
simple distillation
seperates a solvent from a solution. it works because the dissolved solute has a much higher bp than the solvent.
distillation method
salt water is heated
the water vapour cools in the condensor and drips into a beaker
the water has condensed and is now in the beaker snd the solute salt stays behind
fractitional distillation
seperates different liquids from a mixture of liquids. it works because the different liquids have different boiling points.
copper sulfate crystals
preperation of pure, dry sample of a soluble salt from an insoluble oxide or carbonate using a bunsen burner to heat dilute acid and a water bath to evaporate the solvent
copper sulfate method
1. add powdered insoluble reactsnt to acid in a beaker. stir until in excesd
2. filter excess with filter paper. collect the filtrate
3. pour the filtrate into an evaporstibg basin. place on water bath and heat until half of the water of the solution had been removed by evaporation.
4. pour the remaining solution into a watch glsss snd leave in a warm dry plsce for crystallisation
covalent bonds
a covalent bond is formed when 2 atoms share pairs of electrons . occurs most in non metals
small molecules
a substance with small molecules has strong covalent bonds
diamond -giant covalent
-each carbon is joined to 4 other carbons
-form a regular tetrahedral
-no free electrons
graphite
-esch carbon forms 3 covalent bonds with other carbon atoms
-carbon atoms form layers of hexagonal rings
-no covalent bonds between layers
-one delocalised electrin for each atom
graphene
-a single layer if graphite
-hmp
-strong
-has delocalised electrons
fullerene
-carbon atoms with hollow shapes- hexagonal rings of carbon joined by covalent bonds
-weak intermolecular firces
nanotube
a layer of graphene rolled into a cylinder
-high length to diameter ratio
-strong
-have delocalised electrons
metallic bonding
the electrostatic attraction between positive metal ions snd delocalised electrons
alloy
a mixture of chemicsl elemenys where at least one element is a metal
alloy vs metals
many pure metals are too soft so they are made harder by adding another element to the pure metal , forming an alloy
why are alloys so hard
the atoms are different sizes which distort the layors of atoms in a pure metal- which means that a greater force is needed flr the layers to slide over
electrolytes
ionic compounds that molten or dissolved in water
electolysis
a process where electrical energy breaks down electrolytes. the free moving ions in electrolytes are attracted to the oppositely charged electrodes which connect to the dc supply
half equations
show the reaction that happens at an electrifr during electrolysis