chem既問題

Going down Group VII, the elements include F2, Cl2, Br2 and I2 (At2 is usually neglected). All of them have molecular structure, and the molecular sizes are increasing down the group.

The molecules are held together by van der Waals’ forces. The greater the molecular size, the stronger the van der Waals’ forces between the molecules. Therefore, down Group VII, the melting points and boiling points are increasing because of the increase in van der Waals’ forces between the molecules.