The size of the molecules increases down the group. These generally increase with increasing relative molecular mass. Stronger intermolecular forces/attractions implies that you need to supply more energy hence, an increase in melting and boling points. - Size of atoms increases - More electrons - Larger size of molecules - Stronger van der waals forces between molecules - Molecules held together more strongly. Why does volatility decrease down group 7? Why do melting and boiling points increase down group 7? Powered by Create … as u go down a group , with increase in the atomic mass vanderwaal's force of attraction increases, thus increasing the melting and boiling point.Intermolecular forces. The boiling points of group 13 and 14 elements decrease down the group, which is opposite to the trend suggested by van der Waals interactions. Ok, you're looking for a generalization of what happens to the melting point as you go down a column in the periodic table. I suspect that the increase in melting point results from the change in crystal structure and the increasing metallic character of the elements as you go down the group. If you include magnesium, there is no obvious trend in melting points (see below). In group 7 the boiling point increase down the group. Notice how the data for the hydrides of groups 5, 6 and 7 do not follow a smooth trend. This increase in size means an increase in the strength of the van der Waals forces. Generally the melting point of the metals decreases down the group. Boiling points Why does the melting point get lower going down the Alkali Metal Group with increase in atomic number? Opposite of Halogens. In each case the first member of the set has a significantly higher boiling point than would be expected from the boiling points … IN group 1 and 2 the metal become more reactive down the group and are more readily to give up their electrons to non-metals. However, if you include magnesium, you will see that its melting point is lower than the melting point of calcium, the next element down. In group 1 and 2 the melting and boiling point decrease down the group. Stronger intermolecular forces/attractions implies that you need to supply more energy hence, an increase in melting and boling points. F < Cl < Br < I < At. Group 17 elements exist as simple diatomic molecules. There is a general decrease in melting point going down group 2. It is seen that more reactive metal have lower melting and boiling points. Think of the metal atoms as cations $\ce{M^+}$ and anions $\ce{M^-}$ packed into a … For similar reasons the electronegativity decreases. This fact can be best rememberd by the physical states of the halogen molecules. This is because as the metal ions get larger the distance between the bonding electrons and the positive nucleus gets larger and reduces the overall attraction between the two. 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