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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Tom on June 28, 2004, 08:14:05 AM

Title: Physical states
Post by: Tom on June 28, 2004, 08:14:05 AM
I'm having a difficult time figuring out which one of these statements about the general trends of the physical states of the elements is correct? I think the first and third are correct.
Most metals have low boiling points.
the boiling points for the group VII elements increase as the molecular  weight increases.
Most nonmetals have high melting points.
In general, the melting points of the transition metals decreases as you go down the periodic table.

Title: Re:Physical states
Post by: Donaldson Tan on June 28, 2004, 09:10:58 AM
Metals definitely don't have low boiling points. If you mistook this for low melting point, then I must tell you only alkali metals (group 1) exihibit low melting point.

Group VII elements occur as diatomic molecules naturally. Their intermolecular bonding is Van Der Waal's in nature. Their boiling point will definitely increase with molecular weight (as it means these molecules also contain more electrons, hence stronger intermolecular bonding).

Most non-metals have low melting point, with reference to their structures.

Melting point of transition metals increases down the periodic table because there are more delocalised electrons, consequently stronger metallic bond. Hence, the increase in melting point.

Only the 2nd statement is incorrect.
Title: Re:Physical states
Post by: Tom on June 28, 2004, 12:55:38 PM
I understand, thanks for explaining this to me!
Title: Re:Physical states
Post by: Limpet Chicken on June 28, 2004, 03:36:11 PM
Don't forget though, it isn't STRICTLY only group one metals that have low melting points, lead, mercury and gallium also have pretty low melting points too. Mercurs as you know is a liquid at room temperature, lead you can melt with a torch, and gallium will liquify when held in the hand.