What is the difference between polar and non-polar covalent bonding?

Covalent bond = a bond in which the electrons are shared by the partner atoms.

Polar bond = simply a type of covalent bond in which the electrons are shared but not equally. This happens when two different atoms come together, such a C and O. Each atom has a different ability to draw electrons to itself when it shares electrons (that drawing ability is
called Electronegativity).

Polar covalent bond = same as a "polar bond".

Nonpolar bond = two of the same atoms come together, such as the diatomic molecule N2, or triatomics such as O3, etc. A nonpolar covalent bond could be viewed as having "pure" covalent character. There is perfectly equal sharing.

Polar molecule = a molecule in which the polar bonds are disposed in
such a way that it imparts an asymmetry to the molecule as a whole. That
is, it gives the whole molecule a Dipole Moment:

example: water H-O-H has two polar bonds. Since this molecule is
Bent, those two polar bonds ADD TOGETHER to produce a molecule with a
dipole moment. That is, a polar molecule.

example: carbon dioxide O=C=O has two polar bonds also. Since this
molecule is Linear, those two polar bonds ADD TOGETHER to cancel each
other out, to produce a molecule with NO dipole moment. That is, a
nonpolar molecule.

example: carbon tetrachloride CCl4 has four very polar bonds
but these bonds are pointing to the corners of a tetrahedron, and form a very
symmetric arrangement. The polarity cancels itself out, and the molecule is
NONPOLAR.

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.

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