Fig. 1 shows an electron-shell model used by a laboratory that checks the purity of bottled argon for welding. Argon is a noble gas in Group 0. The laborato...
Question 1 Report
Fig. 1 shows an electron-shell model used by a laboratory that checks the purity of bottled argon for welding. Argon is a noble gas in Group 0. The laboratory compares it with chlorine, which is used to disinfect water, and sodium, which is a reactive metal. All three elements are in Period 3. The student is asked to use their electron arrangements to predict their behaviour.
(a) Give the number of outer-shell electrons in chlorine and argon. [2]
(b) Describe why argon is much less reactive than chlorine. [3]
(c) Use the electron arrangements to describe the ions formed when sodium reacts with chlorine. [3]
(d) Draw a dot-and-cross diagram to show the bonding in sodium chloride. Include the charges on the ions. [3]
Answer Details
(a) Chlorine has 7 outer-shell electrons [1] and argon has 8. [1]
(b) Argon has a full outer electron shell. [1] This arrangement is stable [1], so argon does not need to gain, lose or share electrons. [1] Chlorine has one fewer outer electron and can gain one to obtain a full shell.
(c) Sodium loses one electron [1], forming \(\mathrm{Na^+}\). [1] Chlorine gains that electron, forming \(\mathrm{Cl^-}\). [1]
(d) Sodium chloride contains oppositely charged \(\mathrm{Na^+}\) and \(\mathrm{Cl^-}\) ions. The transferred electron is shown as a cross in chlorine's full outer shell. [3]
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