1.1 Mass number == number of protons + number of neutrons
1.2 atomic number == number of protons/electrons
1.3.1 Elements with the same atomic number
but different mass number.
1.3.2 There are more or less neutrons
1.3.3 Some are radioactive.
22.214.171.124 This is due to an unstable nuclei
126.96.36.199 All types of emission are dangerous and
can cause cancer
188.8.131.52 HALF LIFE == the time taken for half the
radioactive nuclei to decay.
184.108.40.206.1 Can be used to determine the age of
220.127.116.11 TRACERS == Radioactive isotopes whose decay is monitored; used
in medicine to aid diagnosis.
18.104.22.168.1 Path is followed by a Geiger counter
22.214.171.124.2 The half life of it cant be
too long or too short.
1.3.4 There is one isotope which is more abundant than
the rest but you can find the average isotopic mass.
1.4 Nuclear fusion is the joining together of 2 or
more nuclei to form a heavier nucleus
1.4.1 Need high temperatures and pressures to
overcome the repulsion between positive
2 LIGHT AND ELECTRONS
2.1 ENERGY LEVELS == Electrons in a hydrogen atom must be in
one of the allowed energy levels. If an electron is in the first
energy level, it must have exactly -13.6 eV of energy. If it is in
the second energy level, it must have -3.4 eV of energy.
2.2 ABSORPTION SPECTRA
2.2.1 Electrons absorb a photon.
126.96.36.199 Excited electrons move up to a higher energy
level ( producing lines on an absorption spectra.
2.2.2 The electromagnetic radiation absorbed by each of
the hydrogen atoms has a definite frequency,
which gives the specific colour.
2.2.3 Coloured background with black lines
2.3 EMISSION SPECTRA
2.3.1 black background with coloured lines.
2.3.2 Electrons first absorb a photon
188.8.131.52 Excited electrons move up to a higher energy level
184.108.40.206.1 Electrons then drop back to lower energy levels
emitting a photon with a certain frequency.
2.3.3 The colour of the lines depends on the
frequency of the photon emitted.
2.4 ELECTRON SHELLS
2.4.1 They fill up lowest first.
2.4.2 period 3 can have more than
3 SHAPES OF MOLECULES
3.1 2 ELECTRON PAIRS
220.127.116.11 180 degress
3.2 3 ELECTRON PAIRS
3.2.1 Trigonal planar
18.104.22.168 120 degrees
22.214.171.124 no lone pairs
126.96.36.199 120 degrees
188.8.131.52 1 lone pair
3.3 4 ELECTRON PAIRS
184.108.40.206 109.5 degrees
220.127.116.11 no lone pairs
3.3.2 trigonal pyramid
18.104.22.168 107 degrees
22.214.171.124 1 lone pair
126.96.36.199 2 lone pairs
188.8.131.52 104.5 degrees
3.4 5 ELECTRON PAIRS
3.4.1 trigonal bypyramid
184.108.40.206 120 degrees
220.127.116.11 109 degrees
18.104.22.168 no lone pairs
3.5 6 ELECTRON PAIRS
22.214.171.124 no lone pairs
126.96.36.199 all bond angles
are 90 degrees
3.6 double bonds repel further
than single bonds
3.7 lone pairs repel more than bonds
3.8 All around a central atom
4 CHEMICAL BONDING AND PROPERTIES
4.1 Metal and Metal == Metallic
4.1.1 Metal ions are arranged regularly
in a lattice
4.1.2 Outer shell of electrons are all shared;
they are delocalised.
4.1.3 Electrons free to move about
therefore can carry a current.
4.2 Metal and Non Metal == Ionic
4.2.1 The Transfer of electrons
188.8.131.52 Usually from the metal to
the non metal.
4.2.2 Form 2 charged ions
in the process
184.108.40.206 Cations == positive
220.127.116.11 Anions == negative
18.104.22.168 Form a giant ionic lattice,
held together by the
between anions and cations.
4.3 Non Metal and Non Metal == Covalent
4.3.1 Sharing of electrons
between two atoms
4.3.2 Double bonds are where two
parsr of electrons are shared
4.3.3 Want to gain a full outer shell.
4.3.4 Dative Covalent Bonding
22.214.171.124 A dative covalent bond is a covalent bond (a
shared pair of electrons) in which both
electrons come from the same atom
5 GROUP 2 REACTIONS
5.1 React with Water
5.1.1 metal + water --> metal hydroxide + hydrogen
5.1.2 more reactive as you go down the group
5.2.1 metal oxide + water --> metal hyrdroxide
126.96.36.199 Alkaline solution is formed
5.2.2 metal oxide + acid --> salt + water
5.3.1 metal hydroxide + acid --> salt + water
188.8.131.52 solutions produced are alkaline
5.3.2 More soluble as you go down the group
5.4.1 Less soluble as you go down the group
5.4.2 metal carbonate --> metal oxide + carbon dioxide
184.108.40.206 thermal decomposition occurs
220.127.116.11.1 Thermal stability increases down the group
6 MASS SPECTROMETER
6.1 Mass spectrometry is an analytical chemistry technique that helps
identify the amount and type of chemicals present in a sample by
measuring the mass-to-charge ratio and abundance of gas-phase ions
6.2 Sample inlet ~ gases or liquids are simply injected but solids
are heated to vaporise them.
6.2.1 Ionisation area ~ a heated filament produces high-energy
electrons. These electrons bombard any atoms or molecules
in the sample and knock electrons out. Cations are formed.
18.104.22.168 Acceleration area ~ an electric field is used to accelerate
any ions so that they all have the same kinetic energy.
22.214.171.124.1 Drift region ~ there is a vacuum here so that ions do not collide with
air molecules which would change the direction of their flight path.
Since kinetic energy = mass*velocity^2 and all ions have the same
kinetic energy , heavier ions more through this region more slowly.
126.96.36.199.1.1 Ion detector ~ light ions reach the detector before the heavier ones. A
computer system converts the informations into a mass spectrum. Only
positive ions are detected after fragmentation
6.3 The mass spectrum for a compound can be much more complex than the mass spectrum on an element.
6.3.1 The ion with the greatest mass corresponds to the molecular mass;
this is called the MOLECULAR ION and corresponds to the parent
molecule minus an electron.
188.8.131.52 The BASE PEAK is the most intense
peak; there are many peaks
because fragments are formed in
the ionisation chamber.
184.108.40.206 The MOLECULAR ION breaks down into
fragments; if the fragment has a positive
charge then it will be accelerated by the
electrical field and detected later.
7 Number of moles = number of particles you have/number of particles in a mole
7.1 Avogadro's constant == 6.02 x10^23
8 THE PERIODIC TABLE
8.1 Periodic Trends
8.1.1 For the metals; melting and boiling points increase across the period because the
metal-metal bonds get stronger as there are more delocalised electrons and decreasing
radius; higher charge density.
8.1.2 The elements with giant covalent structures have strong
covalent bonds linking all their atoms together. A lot of energy is
needed to break these bonds .
8.1.3 Simple molecular substances; their melting and boiling points depend on
the strength of the intermolecular forces. The stronger the intermolecular
forces, the higher the melting and boiling point.
8.1.4 More atoms in a molecule mean stronger intermolecular forces. e.g. in
period 3 sulfur is the biggest molecule so its got higher melting/boiling
points than chlorine.
8.1.5 The noble gases have the lowest melting/boiling points because they exist as
individual atoms resulting in very weak intermolecular forces.
8.2 The modern periodic table is arranged according
to atomic number(proton number)
8.3 In the 1800s, they ordered the periodic table by relative atomic mass.
8.3.1 John Newlands discovered the law of octaves as there were
similar elements appearing at regular intervals.
220.127.116.11 However the pattern broke down in the third row
8.3.2 Mendeleev produced a better table, ordered by by atomic mass
but he left gaps so the elements with similar chemical properties
18.104.22.168 He made predictions about the undiscovered elements, which
later on turned out to be correct