Chemistry Revision

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Chemistry Revision
F331
Isotopes - atoms with the same atomic number, but different mass numbers
131I - radioactive tracer for thyroid. 99Tc for tumours.
Radioisotopes - gamma emitters & short half life - long enough to detect, but not long enough for damage.
Beta particles emitters are more useful than alpha particle emitters because they penetrate more and so are more easily detected. Also, less damaging.
The half life is the time taken for half the isotope to decay
Mass left = initial mass in grams divided by 2 to the power n, where n is number of isotopes.
Factors which can affect accurate determination of an age of rock:
The accurate half-life of a rock must be known
The half life has remained unchanged
No gain or loss of either parent or daughter isotopes
Metamorphism must not have taken place causing resetting of the radiometric clock
The ratio of the two isotopes is constant in a living organism. When the organism dies the Carbon 14 is not replenished so the ratio of carbon 12 to carbon-14 gradually increases
However the half life of carbon-14 is 5730 years and so is useful for up to about 50,000 years old. Beyond this levels of it are so small that errors and so large as to make the measurements too uncertain. Interstellar gas clouds are held together by gravitational forces. These clouds are clumps of denser gas with the most dense gases at the centre. Temperatures are 10,000,000°C and trigger nuclear reactions.
Fusion takes place - large amounts of energy needed to overcome repulsing forces between positive nuclear - high temperatures and high-pressure needed. Periodicity - repeating patterns within the periodic table & regular pattern in a property as you go from left to right across a period.
Electrical conductivity - metallic elements good conductors
Density - increases to a maximum in group 3, then falls.
Ionisation enthalpy - Group 1-troughs - Group 0-peaks.
Melting and boiling points - peaks group 4 - increases up to Group

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