Which statement best explains why rubidium (RbRbRb) reacts more vigorously with water than potassium (KKK)?
The outer 5s5s5s electron of rubidium is more shielded and further from the nucleus than the outer 4s4s4s electron of potassium, resulting in a weaker electrostatic attraction and lower first ionisation energy.
The rubidium atom has a larger nuclear charge (Z=37Z = 37Z=37 vs Z=19Z = 19Z=19), which increases the electrostatic attraction on the outermost electron, making it easier to lose.
The metallic bonding in rubidium is stronger than in potassium, reducing the activation energy required to break the metallic lattice during the reaction.
The hydration enthalpy of the Rb+Rb^+Rb+ ion is more exothermic than that of the K+K^+K+ ion, providing a greater thermodynamic driving force for the reaction.
Practise Edexcel GCSE Chemistry Group 1 with exam-style questions for Foundation and Higher tier. 51 questions, matched to the Edexcel GCSE Chemistry (1CH0) specification and written in Paper 1 and Paper 2 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.
