Some of the elements in the periodic table are metals: (a) The electronic configuration of a metal is 2.8.3 - Edexcel - GCSE Chemistry Combined Science - Question 4 - 2019 - Paper 1

When a small piece of rubidium is dropped into water, it would react vigorously, producing hydrogen gas and creating a characteristic fizzing effect. The rubidium would likely ignite and catch fire due to the heat generated by the reaction.

Lithium has the electronic configuration of 2.1, which means it has two electrons in its first shell and one in its outer shell. In contrast, potassium has the electronic configuration of 2.8.8.1, which means it has a larger atomic radius with a smaller effective nuclear charge acting on its outermost electron. The outer electron in potassium is farther from the nucleus, making it easier for it to be lost during chemical reactions compared to lithium. Therefore, lithium, with its outer electron closer to the nucleus and less shielding, is less reactive than potassium.

To calculate the relative atomic mass of lithium, use the abundance percentages of the isotopes:

1. Calculate the contributions from each isotope:

   • Lithium-6: $7.59\% \times 6 = 0.4554$
   • Lithium-7: $92.41\% \times 7 = 6.4691$

2. Sum these contributions: $0.4554 + 6.4691 = 6.9245$

3. Round to two decimal places: The relative atomic mass of lithium in this sample is $6.92$.