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This question is about the properties of elements in Groups 1, 7 and 0 - OCR Gateway - GCSE Chemistry - Question 20 - 2019 - Paper 4
Question 20
This question is about the properties of elements in Groups 1, 7 and 0. (a) Lithium, sodium and potassium are all Group 1 elements. A teacher adds a small piece of ... show full transcript
Worked Solution & Example Answer:This question is about the properties of elements in Groups 1, 7 and 0 - OCR Gateway - GCSE Chemistry - Question 20 - 2019 - Paper 4
Step 1
Describe what else you would observe.
Answer
When potassium is added to water, the potassium will float on the surface and may move around quickly due to the rapid generation of hydrogen gas. As it reacts, you would observe bubbling or fizzing as gas is released, and the potassium may eventually dissolve. There might also be a slight heat generated due to the exothermic reaction.
Step 2
Explain this trend in reactivity.
Answer
The trend in reactivity down Group 1 can be explained by examining the electronic configurations of the alkali metals. Lithium has the electronic configuration of 1s² 2s¹, whereas potassium has 1s² 2s² 2p⁶ 3s¹. As we go down the group, the outer electron is increasingly further from the nucleus due to additional electron shells, leading to a greater atomic radius. This results in weaker electrostatic forces between the outer electron and the nucleus. As a consequence, it becomes easier for the outer electron to be lost, leading to increased reactivity.
Step 4
Explain why fluorine has a low boiling point.
Answer
Fluorine has a low boiling point because it exists as simple diatomic molecules (F₂) with relatively weak van der Waals forces between them. These weak intermolecular forces require very little energy to overcome, resulting in a low boiling point.
Step 5