Fig. 13.1 shows an incomplete electron arrangement of a neutral atom of element L. Two shells have been drawn with their electrons, and an empty third shell...
Question 1 Report
Fig. 13.1 shows an incomplete electron arrangement of a neutral atom of element L. Two shells have been drawn with their electrons, and an empty third shell is shown. Atom L has a proton number of 15.
Fig. 13.1
(a) Complete the electron arrangement by stating how many electrons should be placed in the outer shell of atom L. [1]
(b) Write the full electronic configuration of atom L. [1]
(c) Deduce the group and period of element L, giving a reason for each. [4]
(d) Predict, with a reason, whether element L is a metal or a non-metal. [2]
(e) Element L forms an ion by gaining electrons. Deduce the charge on this ion and the number of electrons it must gain. [2]
(f) An atom of L has a nucleon number of 31. Calculate the number of neutrons it contains. [1]
(g) Element L is in the same group as nitrogen (proton number 7). Write the electronic configuration of a nitrogen atom and state one way in which the chemistry of L is similar to that of nitrogen. [3]
Answer Details
Element L has 15 electrons, which fill the shells as 2, then 8, leaving 5 for the third shell.
(a) The outer shell must contain 5 electrons [1], since the first two shells hold 2 + 8 = 10 and \(15 - 10 = 5\).
(b) Full electronic configuration: 2,8,5 [1].
(c) Group V [1], because there are 5 electrons in the outer shell [1]; Period 3 [1], because there are 3 occupied electron shells [1]. In general the group number equals the number of outer electrons and the period number equals the number of occupied shells.
(d) L is a non-metal [1]; it lies towards the right of the table and has a nearly full outer shell, so it tends to gain or share electrons rather than lose them [1].
(e) To complete its outer shell L must go from 5 electrons to 8, so it gains 3 electrons [1] and forms an ion of charge 3- [1].
(f) Neutrons = nucleon number \(-\) proton number \(= 31 - 15 = 16\) neutrons [1].
(g) Nitrogen has 7 electrons, so its configuration is 2,5 [1]. Like L it is in Group V, so both have 5 outer electrons [1]; both can gain or share 3 electrons, forming ions of charge 3- and showing the same valency, which is why their chemistry is similar [1].
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