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This question is about elements - AQA - GCSE Chemistry Combined Science - Question 7 - 2020 - Paper 1
Question 7
This question is about elements. Caesium is in Group 1 of the periodic table. 07.1 Explain what happens to caesium atoms and to oxygen atoms when caesium reacts wi... show full transcript
Worked Solution & Example Answer:This question is about elements - AQA - GCSE Chemistry Combined Science - Question 7 - 2020 - Paper 1
Step 1
Explain what happens to caesium atoms and to oxygen atoms when caesium reacts with oxygen to produce caesium oxide.
Answer
When caesium reacts with oxygen, each caesium atom loses one electron to form a caesium ion (Cs⁺). Conversely, each oxygen atom gains two electrons to form an oxide ion (O²⁻). Therefore, two caesium atoms are needed to react with one oxygen atom to form the compound caesium oxide (Cs₂O).
Step 2
Explain why caesium is more reactive than sodium.
Answer
Caesium has more energy levels compared to sodium, which means its outer electron is further from the nucleus. This results in less attraction between the nucleus and the outer electron due to the increased distance and electron shielding. Consequently, less energy is required to remove the outer electron from caesium, making it more reactive.
Step 3
Explain why the early periodic tables placed iodine (I) before tellurium (Te), but then Mendeleev placed tellurium before iodine.
Answer
Early periodic tables were arranged based on atomic masses. Iodine has a lower atomic mass than tellurium, which is why it was placed first. However, Mendeleev recognized that the properties of iodine and tellurium were more similar to those of elements in the same group, thus he placed tellurium before iodine to better align elements with similar properties.