Edexcel GCSE Combined Science: Chemistry: Atomic Structure and the Periodic Table
6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
The model of the atom changed over time as new experimental evidence was gathered. Two important stages were:
- the plum pudding model, in which the atom was a ball of positive charge with negative electrons spread through it;
- the nuclear model, in which there is a tiny, positively charged nucleus at the centre with electrons in the space around it.
The nuclear model was proposed after the alpha particle scattering experiment, in which positively charged alpha particles were fired at a very thin sheet of gold foil.
Explain how the results of the alpha particle scattering experiment led scientists to replace the plum pudding model with the nuclear model of the atom. (6 marks)
A student used paper chromatography to investigate the dyes in a sample of green food colouring. They drew a pencil start line on the paper, added a spot of the colouring, and placed the paper in a solvent. After the run, two dye spots had separated. The student measured the distances travelled, shown below.
| Measurement | Distance / cm |
|---|---|
| Solvent front (from start line) | 8.0 |
| Yellow dye spot (from start line) | 6.0 |
| Blue dye spot (from start line) | 2.4 |
(a) Calculate the Rf value of the blue dye. Show your working. (2 marks)
(b) The yellow dye has a higher Rf value than the blue dye. Explain what this tells you about how strongly each dye is attracted to the paper and to the solvent. (2 marks)
Chlorine exists as two isotopes. Information about them is shown in the table.
| Isotope | Atomic number | Mass number | Abundance / % |
|---|---|---|---|
| chlorine-35 | 17 | 35 | 75 |
| chlorine-37 | 17 | 37 | 25 |
(a) State what is meant by the term isotopes. (1 mark)
(b) Give the number of protons, neutrons and electrons in one neutral atom of chlorine-37. (2 marks)
The Group 1 elements are the alkali metals. Lithium, sodium and potassium all react with water to produce a metal hydroxide and hydrogen gas. As you go down Group 1, the elements become more reactive.
(a) Sodium reacts with water to form sodium hydroxide (NaOH) and hydrogen. Write a balanced symbol equation, including state symbols, for the reaction of sodium with water. (2 marks)
(b) Explain, in terms of electronic structure, why potassium is more reactive than sodium. (1 mark)
Bromine is a Group 7 element. A sample of bromine contains two isotopes: bromine-79 with an abundance of 50% and bromine-81 with an abundance of 50%.
Calculate the relative atomic mass (Aᵣ) of this sample of bromine. Show your working. (2 marks)
The Group 0 elements (such as helium, neon and argon) are the noble gases. They are very unreactive.
State the feature of the electronic structure of a noble gas atom that makes it unreactive. (1 mark)