TBR General Chemistry: Stoichiometry EX 1.17

[Whiteshoes]

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If a molecule is composed of only two elements (X and Y), and if X and Y combine in equal mass quantities, and if Y is less than twice as heavy as X, which of th following molecular formulas is NOT possible?

A. XY

B. XY2

C. X3Y2

D. X3Y

I just dont understand how A,B, and even C can be correct. Their explanation didn't make sense to me. Can someone please DUMB it down for me thanks!

 

[collegestud2013]

You have equal mass quantities of X and Y, so the lighter element must be be present in a higher molecular/molar proportions than the heavier element. In other words, there's an inverse relationship btwn weight of each elment and its molecular/molar abundance in the compound. Take the extreme of the scenario, where Y is EXACTLY twice as heavy as X, then you would have X2Y, but the X:Y ratio cannot be greater than 2:1 because that would require Y to be more than twice as heavy as X. Choices A, B, C have X:Y ratios of less than 2:1, while in choice D it's 3:1, which would require Y to be 3x as heavy as X.

 

[Whiteshoes]

You have equal mass quantities of X and Y, so the lighter element must be be present in a higher molecular/molar proportions than the heavier element. In other words, there's an inverse relationship btwn weight of each elment and its molecular/molar abundance in the compound. Take the extreme of the scenario, where Y is EXACTLY twice as heavy as X, then you would have X2Y, but the X:Y ratio cannot be greater than 2:1 because that would require Y to be more than twice as heavy as X. Choices A, B, C have X:Y ratios of less than 2:1, while in choice D it's 3:1, which would require Y to be 3x as heavy as X.

Makes Sense. Thanks!!