Open Book Paper 2008

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Chemistry  (Salters)

Skills for Chemistry: Open-Book Paper

In radioactive decay, atomic nuclei play an important part in α- and β-decay. α-decay involves the disintegration of an atomic nucleus to emit the α-particle, whereas in β-decay, a neutron inside the atomic nucleus is converted into a proton and an electron, which is released as the β-particle. The particles released are different as well, since the α-particle is made from two protons and two neutrons, similar to a helium-4 particle and the β-particle is an electron. This means that if different elements are formed if the same element went through α- and β-decay.

α-decay

224Ra88                220Rn86        +   4He2

β-decay

225Ra88                225Ac89        +  0e--1

β-decay can happen to any element, from the smallest and lightest, to the largest and heaviest, while α-decay only usually happens in the heavier elements. It usually does not happen in elements with atomic numbers smaller than 83[1]. This means that α-decay usually does not continue past Bismuth and its’ isotopes, whereas β-decay can go all the way to Hydrogen-3, or Tritium (T)[2]:

3T1         3He2  +  0e--1

Radioactive decay is different to Nuclear Fission by the way that the atomic nucleus acts. In Nuclear fission, the nucleus splits after the addition of a neutron, while in Radioactive decay, the nucleus starts off unstable and decomposes. The half-life of elements is also important in radioactive decay because when the element decomposes, it releases either an α- or β-particle. One example is Phosphorous-32, which has a half-life of 14.7 days. After 14.7 days, the mass of the Phosphorous-32 will be halved, and the lost mass will become Sulphur-32, through β-decay[3].

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[I], Diagram showing the half-life of phosphorus-32

Nuclear fission can create a chain reaction, which is why it can be used for providing a lot of energy, unlike radioactive decay, which releases less energy each time a atomic nucleus disintegrates and stops altogether when the element becomes stable.

Hydrogen and helium are important in the synthesis of elements as they are the most common (making up almost 89% and 11% of the universe respectively). The atomic nuclei of the hydrogen and helium are used to make bigger elements through nuclear fusion. It usually starts off with ...

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