Use Lewis electron-dot symbols to represent the formation of

(a)${\mathbf{BrF}}_3$ from bromine and fluorine atoms;

(b)${\mathbf{AlF}}_3$from aluminium and fluorine atoms.

Intermolecular forces are the interaction which are formed by the attraction of the two having opposite charges (partial positive and partial negative charge). The opposite charge are formed by the presence of the electron-negative atom in the molecule. Due to the presence of an electron-negative atom, there is an induced partial positive charge is generated on the electron-positive charge (or less electron-negative charge) atom. There will be an attraction between the both oppositely charges to form a bond.

Lewis dot structure can be defined as the structure formed by using the valence electron of the atom which can be calculated by using electronic configuration.

In this ${\mathbf{BrF}}_3$molecule, halogens are involved in which both are electronegative atoms but the difference in the size of an atom is large as Br-atom is bigger in size than F-atom. The F-atom is more electronegative than Br-atom due to the size difference. The halogens have only one electron in the valence shell. So, the Lewis dot structure is:

In this ${\mathbf{AlF}}_3$molecule, halogens are involved in which one is an electronegative atom and the other is an electropositive atom but the difference in the size of an atom is large as Al-atom is bigger in size than F-atom. The F-atom is more electronegative than Al-atom due to the size difference. The F-atom has only one electron in the valence shell and Al has 3 electrons in the valence shell.

So, the Lewis dot structure is: