atomic mass of each element x number
of atoms present in formula and add up
e.g. (40x1) + (32x1) + (16x4) = 136
Ionic Bonding
Metal reacting
with non-metal
metal atoms lose
electrons and become
positive ions
non-metal atoms gain
electrons and become
negative ions
Oppositely charged ions are
electrostatically attracted
Ionic Lattices
oppositely charged
ions attract each
other in all
directions
melting and boiling points are high because
it is hard to separate the electrons from one
another
Covalent Bonding
atoms of two non-metals
combining
outer electron
shells overlap,
sharing
nuclei of both atoms in a cov. bond
are positively charged
cannot conduct electricity because they
have no charged particles to move
around
cannot dissolve in water
weak intermolecular forces - easily
broken, providing low bp and mp
Covalent Lattices
giant structures
diamond - each carbon atom joined
to four other carbon atoms, hardest
natural substance, cannot conduct
electricity
tetrahedral structure
graphite - each carbon atom in layer is joined
to three other carbon atoms, layers slide over
one another because there are no covalent
bonds, soft=lubricant and pencils, conducts
electricity
silicon dioxide - similar to
diamond structure
Thermosoftening
soften when
heated and can be shaped when hot.
shape will harden when it is cooled, but can
be reshaped when heated up again.
poly(ethene) is a thermosoftening polymer.
tangled polymer chains can uncoil and
slide past each other, making it a flexible
material.
Thermosetting
Once moulded, they do not soften when
heated and they cannot be reshaped.
Vulcanised rubber is a thermoset used to
make tyres. Its polymer chains are joined
together by cross-links, so they cannot
slide past each other easily.
Alloys
in pure metal, all atoms
are the same size and
therefore are very soft
because atoms can slide
alloys disrupt the regular lattice, preventing
layers from sliding due to the myriad of
different sized atoms
Gas Chromatography
separating technique
send gas solvent with analysed substances down a tube
filled with solid material. components travel at dif speeds
and are detected at the end.
OXIDATION IS LOSS, REDUCTION IS GAIN
Empirical Formula
1. work out the relative formula mass
2. find mass of element in compound
3. divide by rel.form. mass x100 to get percentage
Percentage Yield
percentage obtained/maximum theoretical mass x100
Collision Theory
reactants must collide to form chemical reaction.
increasing the temperature provides particles with
more energy, so they vibrate more and heat up
more, causing more collisions to happen.
to cause reaction, particles must collide with sufficient
energy to break bonds - this minimum energy is called
activation energy
Catalysts
chemicals that speed up relations but
are not used up in the process
lowers the activation energy, so that
more collisions happen at a faster
rate, without having to build up to a
higher minimum energy
Endothermic and Exothermic
Endothermic
heat enters the reaction - cools
electrolysis
thermal
decomposition in a
blast furnace
Exothermic
heat exits - warms surroundings through heat transfer