Solutions: Atomic Structure
Q9.
(a) A stable atom contains 28 nucleons.
Write down a possible number of protons, neutrons and electrons contained in the atom.
number of protons = number of electrons (e.g.14) ![](../../../../graphics/symbols/nuclides/ticksmall.png)
number of protons + number of neutrons = 28
(2 marks)
(b) An unstable isotope of uranium may split into a caesium nucleus, a rubidium nucleus and four neutrons in the following process.
![zz](../../../../graphics/symbols/nuclides/uranium236.png)
![z](../../../../graphics/symbols/nuclides/arrow.png)
![z](../../../../graphics/symbols/nuclides/caesium137.png)
![z](../../../../graphics/symbols/nuclides/plus.png)
![z](../../../../graphics/symbols/nuclides/rubidiumX.png)
![z](../../../../graphics/symbols/nuclides/plus.png)
![z](../../../../graphics/symbols/nuclides/4neutron.png)
(i) Explain what is meant by isotopes.
Isotopes are nuclei with nuclei with the same number of protons
but different number of neutrons/nucleons ![](../../../../graphics/symbols/nuclides/ticksmall.png)
(ii) How many neutrons are there in the
nucleus?
137 – 55 = 82
(iii) Calculate the charge to mass ratio, in C kg–1, for the
nucleus.
Q/m = (92 x 1.6 x 10-19)/(236 x 1.67 x 10-27)
Q/m = 3.73 × 107 C kg–1
(iv) Determine the value of X for the rubidium nucleus.
X = 236 – 137 – 4
X = 95 ![](../../../../graphics/symbols/nuclides/ticksmall.png)
(6 marks)
(Total 8 marks)