covalent bond

Unless the two atoms are the same (and have the same atoms bonded beyond them) there is polarisation of the bond. Whether the resultant molecule is polarised (has a dipole) depends upon whether the polarisations of the individual bonds cancel or not.

The situation becomes more complex if the bond is not a single bond. In this case there has to be a further hybridisation of orbitals where the electrons are not directly between the atomic centres but are displaced to either side. The electrons are still associated with the two atoms unless that are other double bonds. It the multiple double bonds can form an aromatic system then the electrons for the aromatic bonds extend over all the atoms of the aromatic system.

Covalent bonding is successfully described with quantum physics, and the quantum model of the atom, unlike rutherfords solar system analogy or bohrs model.

Covalent bonds are chemical bonds where electrons are shared between two atoms. Covalent bonding forms molecules. It occurs when the difference of electronegativity between the two atoms is less than 1.67, except when a metallic bond is formed. If the difference is 1.67 or greater, then an ionic bond is formed. Covalent bonds are formed to let each atom have full outer electron configurations. This consists of typically 8 electrons in the outer electron configuration, however, a configuration of only two electrons also is chemically stable.

Covalently bonded molecules have (in general) low melting points, are in the forms of brittle solids or gases, and are easily dissolved in water, however, when they are dissolved, they do not typically conduct electricity. Covalent bonds are generally weaker than ionic bonds.

Covalent bonds formed between two atoms of the same element are said to be "perfectly covalent" because their electronegativity. This is most common in the seven elements that occur natrually in diatomic form: H, N, O, F, Cl, Br, and I. This causes the only truly nonpolar covalent molecules.