As the atoms get closer together, each electron experiences an attraction towards the two nuclei and the electron density shifts so that the most probable place to find the two electrons is between the two nuclei. Effectively each atom now has a share of both the electrons. The electron density between the two nuclei exerts an attractive force on each nucleus keeping them held tightly together in a covalent bond. A covalent bond forming between two hydrogen atoms. It is also possible for two atoms share more than one pair of electrons, sharing two pairs results in a double bond and sharing three pairs results in a triple bond.
Electronegativity is a measure of how powerful a atom is in a molecule to attract electrons.
Polarization is a term given to name the unequal sharing of electrons in a covalent bond. Molecules that have unequal sharing of electrons are called polar molecules and dipole molecules are ones which have the charge separated, therefore all polar molecules must have a dipole attraction. Non-polar molecules are ones in which there shapes are symmetrical so the electrons are evenly distributed. Polar molecules have a permanent dipole in other words they have a permanent separation of charge. As a result of this, polar molecules are attracted to one another by forces called permanent dipole-permanent dipole interactions, in which the negative end of one molecule is attracted towards the positive end of another.