Question

In a Covalent Bond how The same electron can rotate in two atoms?

We know that in a covalent bond two atoms same the same electron,and acquire their lowest energy state.for this they need to fill their octet or douplet (for hydrogen),but how same electron rotate in both the outer shells of two atoms.

Answer 1

I'll try to address this, but what I say will be repeated much more eloquently in your chemistry text.

Explanation:

From our earliest days as students in chemistry we are introduced to the idea of the ionic bond, where elements exchange electrons to give discrete positive and negative ions, and the covalent bond, in which electrons are shared between nuclei.

The ionic bond is fairly intuitive. For instance, sodium is oxidized by chlorine to give `Na^+` and `Cl^-` ions that are bound in a non-molecular, infinite array by electrostatic bonds. On the other hand, the covalent bond is supposed to result from the sharing of 2 electrons between nuclei. But why should a pair of electrons bind together?

The modern covalent bond is conceived to be a region of high electron density between 2 positively charged atomic nuclei. The atomic nuclei are attracted to the region of electron density. If the nuclei get too close, the positive nuclei repel each other electrostatically, if they get too far from each other, their mutual attraction diminishes.

The sweet spot, the equilibrium distance, where mutual attraction is maximized, and internuclear repulsion is minimized is by definition the equilibrium bond length. The 2 electrons (assumed to be derive from 1 electron from each atom) combine in a bonding orbital, that whose equilibrium distance defines the bond length. This is what chemists mean when they say covalent bonding is the result of the sharing of electrons.

Modern theories of chemical bonding identify so-called bonding orbitals, where electron density is concentrated BETWEEN nuclei, and corresponding, higher energy anti-bonding orbitals, where electron density is concentrated way from the atom/atom vector. The lower energy bonding orbitals are filled first, and result in covalent bonds.

The chemical bond, the region of overlap of electron density, is to a first approximation rotationally symmetric. The bond remains secure in spite of rotation about the atom-atom vector. Higher order bonds, i.e double bonds, can preclude this rotation.

Of course, I should illustrate this spray with some diagrams, but as I am on a slow connection this is difficult. You should find plenty such diagrams in your text. But please try to digest what is written in your text as well.