Higher melting point, PH3 or NH3?

  1. Hi everyone, I have a question for all of you

    In an exercise of chemistry it's written to find the compound, between every couple, which has the highest melting point.

    The three couples are: H20 H2S; KBr CF4, NH3 PH3.

    In the first case water has higher melting point because the bond is stronger than the sulfuric acid one.
    In the second case, looking at the electronic configuration, we can spot that Br has 4p5 and so makes an ionic bond with K that is giving away its electron to complete valence shell.

    In the third case i really don't know what to think.
    They have same electronic configuration so i don't know how to spot the higher one..
    Can anybody help me? :)
    Thank you.
     
  2. jcsd
  3. SpectraCat

    SpectraCat 1,395
    Science Advisor

    Well, what are the dominant intermolecular forces between ammonia molecules? Do you expect those to be stronger or weaker than the forces between phospine molecules? Is there any similarity between this pair and the other pairs you considered?
     
  4. H2S is not sulfuric acid. H2S is hydrogen sulfide.
     
  5. Look at the Electronegativity
     
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