If a water molecule is neutral, how do water molecules attract one another by electric force and form water?

Question

If a water molecule is neutral, how do water molecules attract one another by electric force and form water?

This makes no sense to me (I'm new to physics) and my textbook didn't explain this well.

Answer 1

The water molecule is neutral on overall basis, i.e., the water molecule as a whole has no net charge.

The water molecule is not linear rather it has a bent shape with two hydrogens on the same side. This happens because of the lone pair-bond pair repulsions.

The oxygen is a more electronegative element than hydrogen, i.e., oxygen has high electron-attracting power. Therefore, it attracts the bond pair electrons towards itself which gives a partial negative charge to the oxygen and a partial positive charge to the hydrogen. This gives a possibility of the positive part of a molecule being attracted towards the negative part of another molecule.

This is how water molecules attract each other. The bonds formed between the hydrogens and the oxygen are termed as hydrogen bonds and these bonds are quite strong, which is why water with very low molecular mass has unusually high melting and boiling point.

As a matter of fact, even molecules with zero dipole moment can also attract each other. There exist weak Van der Waals forces (London Dispersion Forces) which are caused by induced dipoles. This is responsible for helium to to stay in liquid form at 4K.

London Dispersion Force - Induced Dipole Forces

Answer 2

This is a more general answer.

Atoms and molecules are quantum mechanical entities. This means that the "shape" of atoms depends on the solution of quantum mechanical equations, which give probabilities for locating in space the electrons that are bound to the nucleus of the atom with the electric potential provided by the protons of the nucleus. The electrons are located in atomic orbitals around the much smaller in space nucleus which have the quantum numbers of the solutions.

In this orbitals table one can see the complicated shapes available in space for the negatively charged electrons. What happens to the electric field of an atom with these, almost LEGO like orbitals, is the following: where the electrons are, the positive charge of the nucleus is neutralized/shielded, but where they are not, the positive charge dominates and thus even though overall the atom is neutral in space it has an electric field with attractive and repulsive possibilities in spatial orientation.

Thus an atom can form a stable molecule with an other atom of its species, as O2 for example, the atoms fitting each other like LEGO blocks.

Molecular orbitals have a similar topological logic :

Suitably aligned f atomic orbitals overlap to form phi molecular orbital (a phi bond)