AQA AS Chemistry Unit 1

Revision notes on Chem 1 for AQA AS Level

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  • Created on: 23-05-11 17:51
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Chemistry 1 Revision
Atomic Structure
Atomic number of an atom is the number of protons within its nucleus - symbol X
Mass number of an atom is the number of sub-atomic particles in its nucleus, it is the
addition of neutrons and protons - symbol A
Isotopes are atoms that have the same number of protons but different numbers of
neutrons in their nuclei.
o Different isotopes of an element are chemically identical to each other because
they contain the same number of protons and electrons
Mass Spectrometer is a machine that can analyse samples of elements
o Ionisation - Ionised the particles so that they can be accelerated, deflected and
detected
High energy electrons from an electron gun, these electrons hit the
atoms and knock an electron off.
X(g) + e- => X+(g) + 2e-
o Acceleration - Have to be accelerated so that they can move through the mass
spectrometer - Attracted to negatively charged plates and pass through narrow
slits in them
Focuses the ions into a narrow beam
Makes the ions in the sample move quickly
Vacuum pump - removes air which stops molecules from getting in the
way of the speeding ions
o Deflection - Magnetic field produces a force to deflect the ions, depends on the
size of the charge on the ion, if they all have the same charge it depends on the
ions mass
Lighter ions will be deflected the most
Heavier ions will be deflected the least
Only ions with the right mass and charge will be deflected round the
bend
o Detection - Ionised so can produce an electric current in the detector
Detector contains a negatively charged plate
An electric current is produced each time an ion hits it
o The more ions the bigger the current
Current is recorded as a peak in a mass spectrum
Different ions in sample are brought to
the detector by altering the strength of
the deflecting magnetic field
The amount that an ion is deflected in the mass spectrometer depends on its mass to
charge ratio
o Relative mass of the ion M divided by its charge Z
Ions with the same m/z ratio will be deflected by the same amount so it
is unable to tell them apart
Relative Isotopic Mass = Mass of One atom of the isotope ÷ Mass of one atom of 12C ×
12

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Graph of shows Relative Abundance of each ion on the Y axis and m/z ratio on the X axis
o This shows which isotopes are most common
o Using the information we can work out relative atomic mass
o The tallest peak is called the base peak
Relative Atomic Mass = Mean mass of an atom of an element ÷ Mass of one atom of 12C
× 12
AR = Sum of (m/z × Relative Abundance) ÷ Sum of Relative Abundances
Electron sub shells
o…read more

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Has an outer electron in the p sub-shell
Higher in energy than outer electron in
magnesium
o As a result less energy is needed to remove it
Sulphur
o Has an outer electron in the 3p sub shell
In phosphorous the 3p electrons are unpaired
In sulphur two of the 3p electrons are
paired
o There is repulsion between
paired electrons in the same sub
shell
Less energy is needed
to remove one of the
paired electrons from
the sulphur
o Increasing ionisation energies
General…read more

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Elimination reactions involve removing a group of atoms from a molecule
Condensation reactions involve two molecules joining together to make a larger
molecule and a smaller one
C= n ÷ V
o C = concentration in mol dm-3
o N = amount of substance in mol
o V = volume in dm3
A standard solution is a solution with an accurately known concentration
Bonding and Periodicity
Ions
o Ionic compounds have a strong electrostatic force of attraction between
oppositely charged ions in an ionic compound…read more

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One of the atoms contributes both of the shared electrons
Shown by an arrow from the donating atom to the receiving atom
Shapes of molecules
o Linear
Bond angle = 180 degrees
o Trigonal planar
Bond angle = 120 degrees
o Tetrahedral
Bond angle = 109.5 degrees
o Trigonal bipyramidal
Bond angle = 120 degrees (Equatorial) and 90 degrees (Axial)
o Octahedral
Bond angle = 90 degrees
o V - Shaped
Bond angle = 104.…read more

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Lone pair of electrons on the nitrogen, oxygen or fluorine atom
The single electron on the hydrogen is drawn away by the
electronegativity of the N, O and F atom
o The H atom is then strongly attracted to the lone pair of
electrons on the N, O or F on another molecule
`A hydrogen bond is formed!
Evidence for this can be seen in the boiling points of substances in group
hydrides
Group 5 NH3 has a boiling point higher than expected and Group…read more

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Structural formula shows the number and type of each atom in a molecule and how they
are joined together
Displayed formula is the actual drawing of the alkane
Shortened structural formula is the CH3CH2CH2CH3 for example
Meth - 1 Eth -2 Prop - 3 But -4 Pent -5 Hex - 6 Hept - 7 Oct - 8 Non - 9 Dec - 10
Structural isomerism occurs when two or more organic compounds have the same
molecular formulae but different structures - gives different chemical and…read more

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Unburned hydrocarbons are oxidised to carbon dioxide and
water vapour
Acid rain is rain that is more acidic than normal
o Sulphur dioxide dissolves in water vapour to form sulphurous acid which is then
oxidised to form sulphuric acid
o Flue gases are waste gases from boilers and furnaces
Flue gas desulphurisation is a process that removes sulphur dioxide
Removed using a base such as calcium oxide
Calcium hydroxide is produced by reacting calcium oxide with water
Reacts with sulphur dioxide
o To form calcium…read more

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