Hydrogen fluoride molecule

The image below is a representation of the electron cloud about the hydrogen and fluorine atoms.

The electron clouds about each atom in this molecule are not identical. The electrons are not shared equally between the two nuclei because the H atom and the F atom do not attract electrons towards their nuclei equally. The unsymmetrical distribution of the electron cloud shows that the electron cloud is distorted in the direction of the more electronegative F atom. This observed shift of electron cloud leaves the H end of the molecule slightly positive when compared to the F end. The bond that forms in the HF molecule is a polar covalent bond.

To represent an imbalanced of electron cloud, the symbol δ+ is written by the H end of the molecule to indicate that the molecule has a slightly positive charge with respect to the F end.

The δ+ is written by the F end of the molecule to indicate that the molecule has a slightly negative charge with respect to the H end.

Properties of polar molecules

The separation of charge in a polar covalent bond creates an electric dipole. If polar molecules, such as HF, HCl, HBr, and HI, are subjected to an electric field, they tend to line up in a direction of the field.