What type of bonds are classified as non-polar covalent?

Non-polar covalent bonds are characterized by an equal sharing of electrons between two atoms due to their similar electronegativities. The electronegativity difference for these bonds is typically very small, which allows for an even distribution of electron density. Specifically, a difference in electronegativity values less than 0.4 indicates a non-polar bond. This means that the atoms involved in the bond attract the shared electrons equally, resulting in minimal charge separation.

In contrast, a value greater than 0.7 generally indicates a polar covalent bond, where there is significant uneven sharing of electrons due to a larger electronegativity difference between the two atoms. Additionally, bonds formed between metals and non-metals typically involve ionic bonding rather than covalent bonding, which is characterized by the complete transfer of electrons, as mentioned in the last choice. Thus, having a difference in electronegativity less than 0.4 accurately describes the non-polar covalent bonding situation.