Melting Point and Boiling Point

By: Danny, Jiyoung and Nirali

Definitions

Melting point: The point at which a solid becomes a liquid.    Boiling Point:  The point at which a liquid boils and turns into vapor.

Trend Across the Row

For both melting and boiling points, the general periodic trend is increasing to the middle of block d and then decrease to the noble gases. The highest melting and boiling point are apparent at the middle of the transition metals because of electron-electron repulsion. The electron-electron repulsion causes the element to be less stable thus, making it easier to break apart which in turn, causes a lower melting or boiling point. There is the least amount of electron-electron repulsion in the middle of block d. 

Trend down the Column

There is no easily identifiable trend for both melting and boiling points for columns. Some groups increase melting and boiling point while going down the column, others decrease, and others have no clear trend whatsoever. Melting and boiling points increase when electron-electron repulsion decreases. Since electron-electron repulsion decreases going down columns on the periodic table, we would expect to see melting and boiling points increase, though we can see that this isn't always the case.

Units of the Trend

• Fahrenheit• Celsius• Kelvin 

Exceptions to the Trends

Since there are only general trends for melting and boiling points, there aren't really exceptions to the trends. In this case, exceptions would be any rows or columns that don't follow the expected trends.