Atomic orbitals are often represented as electrons spinning around the nucleus (top - carbon). However, orbital shells actually represent the volume in which the wave-form electron is likeliest to be found (shaded).
As such, orbitals are more akin to a cloud around the nucleus (bottom - sp hybrid hydrogen).
The location of electrons within orbitals is described mathematically by the Schrodinger equations. Computer simulations reveal probability distributions for orbitals.
Table of images of orbitals / Scatter plot of probabilities / interactive / virtual text / virtual text orbitals / download audio-anim of H2 bonding / audio-anim of hybridization of s p orbitals / voxel movie of orbital / movie 2 / movie 3 / movie 4 /
Atomic orbitals are distorted in molecular covalent bonds, where atoms share electrons within a molecule.
When electrons are shared between two atoms of the same element, the electrons are shared equally, creating a non-polar covalent bond.
When electrons are shared between atoms of different elements, the electrons are not shared equally. Unequal sharing results in a polar covalent bond in which the increased-probability cloud over one atom has a slightly negative charge compared to a slightly positive charge over the other -- a dipole.