Fig. 5.1 shows the electron arrangements of atoms of two different elements, L and M. The letters are not the chemical symbols of the elements. (a) State th...
Question 1 Report
Fig. 5.1 shows the electron arrangements of atoms of two different elements, L and M. The letters are not the chemical symbols of the elements.
(a) State the feature of the electron arrangements that L and M have in common, and state which part of the periodic table (group or period) is fixed by this shared feature. [2]
(b) Use the diagrams to state which of L and M is in the earlier (lower-numbered) period, and explain how the diagrams show this. [2]
(c) Explain, in terms of electronic structure, why M is more reactive than L. [3]
(d) State the charge of the ions formed by L and M. [1]
(e) Write a balanced symbol equation for the reaction of M with water. Use the symbol M in your equation and assume M behaves like a typical Group I metal. [2]
(f) State the trend in melting point on going from L to M and predict how the melting point of the next element in the same group would compare with that of M. [2]
Answer Details
What this tests: using shell diagrams to place Group I metals and explaining the reactivity trend down a group.
(a) Shared feature [2] Both L and M have one electron in their outer shell [1]; the number of outer electrons fixes the group, so both are in Group I [1].
(b) Earlier period [2] L is in the earlier (lower-numbered) period [1]; L has 2 occupied electron shells while M has 3, and the period number equals the number of occupied shells [1].
(c) Why M is more reactive [3] Reactivity increases down Group I. M has more electron shells, so its single outer electron is further from the nucleus [1]; there is also more shielding by the inner shells [1]; so the nucleus holds the outer electron less strongly and it is lost more easily, making M more reactive than L [1].
(d) Ion charges [1] Both form ions with a charge of 1+, since each loses its single outer electron.
(e) Reaction of M with water [2]
\[ 2M + 2H_2O \rightarrow 2MOH + H_2 \]1 mark for the correct products (the hydroxide MOH and hydrogen gas), 1 mark for balancing.
(f) Melting point trend [2] The melting point decreases from L to M [1]; the next element down the same group would have an even lower melting point than M [1].
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