Elements of life
- Created by: Science
- Created on: 20-04-21 18:00
Elements of life
Atomic model
- John Dalton = solid spheres
- JJ Thompson = plum pudding model
- Rutherford = nuclear model
- Henry Mosely = nuclear charge increases by 1
- James Chadwick = neutron
- Bohr = Bohr model
Isotope - atoms of the same element with the same number of proteons but a different number of neutrons
Releative atomic mass - average of relative isotopic masses taking into account abundances, releative to 1/12 of a carbon 12 atom
Nuclear fusion
- two light atomic nuclei fuse to form a new single heavier nucleus of a new element.
- only at a high temperature and pressure
Elements of life
Mass spectroscopy
- measures atomic mass and abundance of isotopes
- separates on mass:charge ratio
Absorption spectrum - visible light spectrum with black lines
Emission spectrum - black spectrum with coloured lines
Wave theory
- light behaves like a wave
- speed of light = wavelength x frequency
Particle theory
- light is a beam of photons
- energy = plank constant x frequency
Elements of life
Bohr's theory
- electrons in indefinite shells
- electrons move up shells by absorbing frequencies, emit frequencies when they move back down
- energy levels closer at higher frequencies
- energy of photon equal to difference between two energy levels
Shell sizes
- n=1 - 2 electrons
- n=2 - 8 electrons
- n=3 - 18 electrons
- n=4 - 32 electrons
Subshells
- s subshell = 2 electrons
- p subshell = 6 electrons
- d subshell = 10 electrons
- f subshell = 14 electrons
Elements of life
Orbitals
- holds two electrons each with opposite spin
- s orbital = spherical
- p orbital = dumbell shaped
- half shell stability - electron promoted so all half shells are full
Periodic table
- Mendeleev - atomic mass order, grouped with same properties
- today - atomic number order
Melting points periodicity
- Groups 1-4 increasing, due to giant metallic structure
- Groups 4-5 sharp increase, due to giant covalent structure
- Groups 5-0 low, due to simple covalent structure
Elements of life
Water of crystallisation
- water inside a crystal lattice
- pentahydrate = 5 moles of water
Ideal gas equation
- molar volume - 1 mole of any gas at RTP has a volume of 24 dm-3
Yields
- percentage yield = actual yield/theoretical yield
- never 100% due to unwanted side reactions, impurities and equilibrium system
Covalent bond - shared pair of electrons attracted to both nuclei
Dative covalent bond - shared pair of electrons provided by 1 atom only, normally occurs with ions
Elements of life
Shapes of molecules
- Valence shell repulsion theory - electron pairs repel each other as far apart as possible
- lone pairs have a stronger repulsion so reduce angle by 2.5 degrees
Molecule shapes
- linear = 2 areas of electron density,180 degrees
- trigonal planar = 3 areas of electron density , 120 degrees
- tetrahedral = 4 areas of electron density, 109.5 degrees
- pyramidal = 4 areas of electron density, 1 lone pair, 107 degrees
- non-linear = 4 areas of electron density, 2 lone pairs, 104.5 degrees
- trigonal bipyramidal = 5 areas of electron density, 120 degrees and 90 degrees
- octahedral = 6 areas of electron density, 90 degrees
Elements of life
Ionic structure
- loss/gain of electrons creating an electrostatic atraction between positive and negative ions
- giant regular lattice
- high melting point/boiling point
- only conducts electricity as molten or aqueous
Metallic structure
- metal cations regularly arranged in a sea of delocalised electrons
- giant metallic lattice
- high melting point/boiling point
- conduct electricity
Simple covalent
- small groups of atoms covalently bonded with weak intermolecular forces
- low melting point/boiling point
- don't conduct electricty
Elements of life
Giant covalent structure
- high melting points/boiling points
- good thermal conductors
- can't conduct electricity
- insoluble in polar substances (no ions)
Polymers
- long chain molecules
- low melting points/boiling points
- don't conduct electricity
Group 8 - monatomic, weak forces of attraction
Elements of life
Ionisation enthalpy- energy required to remove one electron from every atom in one mole of a gaseous element
Factors affecting enthalpy
- nucleus charge - more protons = stronger attraction
- disrance - smaller distance = weaker attraction
- electron shielding - electrons between electron and nucleus so nuclear attraction is weaker
- half shell stability - electrons not repelled by each toher so more energy required
Standard solutions
- C1V1 = C2V2
- stock solution = original standard solution
Acid and bases
- amphoteric - acts as an acid and base
- Bronsted - lowery theory - acid proton donor, base proton acceptor.
Elements of life
Group 2 theory
- alkaline earth metals
- reactivity increases down the grop
- thermal decomposition - MCO3 --> MO + CO2
- hydroxide solubility increases down the group
- carbonate solubility decreases down group
Carbonates of group 2
- thermal stability increases down group
- metal ion polarises negative cloud around carbonate making it less stable so it thermally decomposes
- charge density (meaaure of concentration of a charge on an ion) decreases down group 2
- higher charge density = higher thermal decomposition
Oxonium ion
- hydrogen from dissolved acid attracted to negative region of water molecule forming dative covalent bond
- proton can then be donated
Elements of life
Solubility rules
- group 1 and ammonia soluble
- all nitrates soluble
- Halides soluble except lead and silver
- sulfates soluble except lead, silver, barium and calcium)
- hydroxides and carbonates insoluble except group 1 or ammonia
Precipitation reaction
- two soluble salts mixed and then filtered to makes insoluble salt
Soluble salt production with metal/insoluble base
- add metal/base in excess to acid. Filter and carry out crystallisation
Soluble salt production
- Titration with indicator
- calculate average of concordant results (between 0.1 of each other)
Elements of life
Sodium hydroxide test
- silver = brown precipitate
- calcium = white precipitate
- copper = blue precipitate
- lead = white precipitate
- Iron II = green precipitate
- Iron III = red/brown precipitate
- Zinc/aluminium = white and redissolved in excess NaOH
Carbonate test
- add HCL
- bubblr through limewater, cloudy means carbon dioxide present
Sulphate test
- add dilute HCL to remove carbonate
- Add barium chloride - white precipitate means sulphate present
Elements of life
Test for hydroxide
- Dip red litmus paper into solution. Turns blue.
Test for Halides
- add dilute nitric acid
- add silver nitrate
- chlorine = white precipitate
- bromine = cream precipitate
- iodine = yellow precipitate
Adding dilute ammonia to halide test
- silver chloride redissolves
- silver bromide redissolves in concentrated ammonia
- silver iodide won't redissolve
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