why does mealting point decrease from As to Bi
Answers
here is ur answer,,,,,,.............................................
Boiling points of the elements increases down the group mainly because the mass increases.
Melting point on the other hand depends on the energy required to overcome the inter-molecular interactions and break the vanderwall forces between the molecules. At the top of the group we have Nitrogen which deadly forms covalent bonds and the molecule is N2. Then we have Phosphorus which too has a tendency for covalent bonds but now the molecule is P4 causing the requirement of larger amount of energy to break it. Arsenic has a bigger array of atoms like in Silicon hence making it tough to break them apart. Now you see as we go further down the group, the metallic nature of elements increases due to poor shielding by newly introduced d and f orbitals. The loosely held electrons give rise to weak interactions. Arsenic as you know is a metalloid, so it is the point of inversion of the strength of interactions. Hence, melting point increases upto Arsenic and decreases down till Bismuth.
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Melting point from nitrogen to arsenic increases & from arsenic it decreases upto bismuth because down the group as the size of the element increases the tendency of elements to form three covalent bonds increases (inert pair effect).