What is required for two atoms to share electons equally in a chemical bond?

Answer 1

the electrons are shared equally between two atoms because they need eight electrons on the valence(last) shell so that the elements can reach a state of stability. The idea here is to have the elements have the same amount of electrons on the last shell as those in the noble gas group.

Let's consider covalent vs. ionic bonds to see what the difference is. We say a bond is ionic when electrons spend much more time around the more electronegative element. That is, we classify the bond type based on the electronegativities of the participating elements (Electronegativity is a measurement of an element's ability to 'steal' electrons). We say that a bond is ionic when the difference in electronegativities is around 0.5 or more.

ENhigh - ENlow > 0.5 ----- Ionic bond

ENhigh - ENlow < 0.5 ----- Covalent Bond

Sodium has EN = 0.9. Chlorine has EN = 3.0

3.0 - 0.9 = 2.1, NaCl is an ionic bond

Carbon has EN = 2.5. Hydrogen has EN = 2.1

2.5 - 2.1 = 0.4, CH4 has covalent bonds

Answer 2

To share electrons equally, two atoms should have the same electronegativity.