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Melting point across period 3

Hi, can anyone explain why the melting point decreases from S to Ar? From S-Ar, there are more electrons, so surely the London forces become stronger from sulfur to argon, but why is there a decrease in the melting point from S to Ar?

Thanks
Original post by coconut64
Hi, can anyone explain why the melting point decreases from S to Ar? From S-Ar, there are more electrons, so surely the London forces become stronger from sulfur to argon, but why is there a decrease in the melting point from S to Ar?

Thanks


Don't forget that London forces are intermolecular so you have to consider the molecular formula. Sulfur exists as S8 crown shaped cyclic molecules.
This means that it has a relative mass of 8 x 32 = 256 as compared to 40 for Argon, which is monatomic.
Reply 2
Original post by charco
Don't forget that London forces are intermolecular so you have to consider the molecular formula. Sulfur exists as S8 crown shaped cyclic molecules.
This means that it has a relative mass of 8 x 32 = 256 as compared to 40 for Argon, which is monatomic.


Thanks. I get it now, so sulfur can exist as S8, phosphorus is P4 but Ar just an individual molecule.

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