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Topic 2 and 12 - Atomic Structure (Theory (Models (Bohr Model - 2n^2 -…

- - - - Similarities between isotopes
        
        similar chemical properties
        
        same proton and electron number
        
        Differences between isotopes
        
        different mass/neutron numbers
        
        different rates of diffusion
        
        different densities
        
        nuclear reactions, heavier isotopes are radioactive decays
        
        melting/boiling points differ
      - Radioactive isotopes:
        14C in radiocarbon dating
        Living things constantly accumulate carbon-14 but the isotope decays with a half-life of 5730 y.
        After death, accumulation stops but the decay continues, so the ratio of carbon-14 to carbon-12 can be used to calculate how long ago death occurred.
        This can be used to date organic material from archaeological sites.
        60Co in radiotherapy
        Cobalt-60 emits gamma radiation which can be directed onto tumours in an attempt to kill their cancerous cells. Whole-body irradiation can be used to destroy bone marrow before a transplant is attempted.
        131I and 125I as medical tracers
        The thyroid is the only organ of the body which accumulates iodine, so isotopes of iodine can be used to study thyroid disorders. Iodine-131 or iodine-125 are given to patients in very low doses, and the pattern of radiation can reveal tumours or other abnormal growths. Larger doses of iodine radioisotopes can be used as therapy for thyroid cancer.
  - - - Electrons are excited (usually by running an electric current through them). This causes electrons to 'jump' into higher electron shells ( X -> X* ) this state is only temporary, however, and the electron falls back to its ground state. This change (When the electron falls back from the higher shell to a lower one) decreases the energy of the electron, and this energy is emitted in the form of a photon. If this photon falls into the visible spectrum of light, then it produces a visible spectrum. As electrons move further away from the nucleus, the electron shells become closer together in terms of space and energy, and so lines converge towards the end of the spectrum.
        
        When hydrogen gas is stimulated, it emits a characteristic set of spectral lines. The gas is usually stimulated by passing a current through a sample of the gas at low pressure, but the same effect occurs if hydrogen gas is heated strongly.
        The spectral lines have the following characteristics:
        There are several series of lines, which become more closely packed at higher frequencies (lower wavelengths) until finally the series ends.
        The highest frequency series, discovered by Lyman, is in the ultraviolet. Lower frequency series are in the visible and infrared
- - - - Reasons for drops/ inconsistencies in graphs
        Unstable, incomplete orbital (ionises quicker)
        When electrons are paired, the extra mutual repulsion results in less energy being required to remove an electron, hence a reduction in the ionisation energy.
        (Compare the electron configuration shells of Phosphorus and sulphur)
  - - - Each shell is divided into further sub-levels which are s, p, d, f. Each letter describes a different orientation in space, each with it's own energy. s has the lowest energy, followed by p, d and f
        
        S oribital: spherical in shape. Only one s orbital per shell which can hold a maximum of 2 electrons as long as they have different spin quantum numbers
        
        P oribtal: starts from the second shell. Has 3 angular nodes px, py and pz (therefore requires three bpxes to be drawn). Can hold a maximum of 6 electrons. They are degenerate, meaning they have the same energy and are often involved in bonding.
        
        D orbital: Starts from the third shell. 5 boxes, maximum of 10 electrons. They are degenerate and can sometimes split and have different energies. They are sometimes involved in bonding - especially in inorganic chemistry.