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Ruse prelims chem (1 Viewer)

Luukas.2

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It's a badly written question

If it means which of the options is the electron configuration of element X in its elemental form, then none of them is correct, but the best answer is C.

If it means which of the options is the electron configuration of the form in which X exists in the compound XCl3, which is implied to be X3+, then none of them is correct, but the best answer is A.

However, the compound AlCl3 is not ionic.
 

eternallyboreduser

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It's a badly written question

If it means which of the options is the electron configuration of element X in its elemental form, then none of them is correct, but the best answer is C.

If it means which of the options is the electron configuration of the form in which X exists in the compound XCl3, which is implied to be X3+, then none of them is correct, but the best answer is A.

However, the compound AlCl3 is not ionic.
Hmmm i find it strange how AlCl3 isn’t ionic, ik that it’s difference in EN isn’t larger than 1.7, however, it is still a metal and non metal, no?
 

eternallyboreduser

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It's a badly written question

If it means which of the options is the electron configuration of element X in its elemental form, then none of them is correct, but the best answer is C.

If it means which of the options is the electron configuration of the form in which X exists in the compound XCl3, which is implied to be X3+, then none of them is correct, but the best answer is A.

However, the compound AlCl3 is not ionic.
Also neon and chlorine don’t form an ionic compound either, both are non metals and their differences in EN is 1.34
 

Luukas.2

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Hmmm i find it strange how AlCl3 isn’t ionic, ik that it’s difference in EN isn’t larger than 1.7, however, it is still a metal and non metal, no?
Aluminium chloride is a covalent molecular substance, which actually exists primarily as a dimer, Al2Cl6.

It reacts violently with water as the chloride ligands are displaced to produce its hydrate form, AlCl3.6H2O, which is much more accurately represented as [Al(H2O)6]Cl3, and which subsequently decomposes to a mixture of aluminium oxide and aluminium hydroxide with the release of hydrogen chloride gas. Reactions in which a solution of aluminium chloride is allegedly produced are actually producing this hydrate form with separated ions. So, for example, adding aluminium oxide into hydrochloric acid actually reacts:

Al2O3 (s) + 6 HCl (aq) + 9 H2O (l) ---> 2[Al(H2O)6]3+ (aq) + 6 Cl- (aq)​

Evidence of this can be seen in that (like dry ice / carbon dioxide), solid aluminium chloride sublimes (turns directly from solid to gas as it has no liquid phase at atmospheric pressure) at about 180 degrees Celsius. Compare this to actual ionic compounds of aluminium, like:
  • aluminium oxide, Al2O3, MP = 2072 oC, BP = 2977 oC
  • aluminium nitride, AlN, MP = 2500 oC
  • aluminium phosphate, AlPO4, MP = 1800 oC
I said this was a bad question because, firstly, it is ambiguous whether it seeks the electronic configuration of X or X3+, and secondly, the compound in question might be formally attributed as having X in a +3 oxidation state, but the actual substance is not at all like that might imply.

The electronegativity guidelines are useful as guidelines, but chemistry is much more complicated than such simple rules might suggest. Another excellent example is titanium tetrachloride, which is a covalent molecular liquid at room temperature... compare it with titanium(II) chloride (ionic), which melts above 1000 oC, and titanium(IV) oxide (also ionic), which melts above 1800 oC.
 

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