Question

In the formation of NaCl, Na gets oxidised because it loses an electron, while Cl gets reduced because it gains an electron.

But how does this concept work in the case of covalent compounds, especially those compounds that have non-polar bonds?

For example, according to my textbook, in the formation of methane Hydrogen is getting oxidised from state 0 to 1, while Carbon is getting reduced from state 0 to -4.

But how is hydrogen losing an electron here? Doesn't it gain an electron due to sharing? C-H bonds are non polar so we cannot say that carbon pulls hydrogen's electrons towards it either right?

Answer 1

In covalent compounds like methane, hydrogen is considered oxidized and carbon reduced based on changes in oxidation states, which are assigned according to electronegativity differences that infer uneven electron sharing, even in nonpolar bonds.

Step-by-step explanation:

In the formation of covalent compounds like methane, the concept of oxidation and reduction refers to the changes in oxidation states of the elements involved rather than the actual transfer of electrons as in ionic compounds. In the case of methane (CH4), the hydrogen atoms do not literally lose electrons but are considered to be oxidized because their oxidation state increases from 0 in H2 to +1 in CH4. The carbon atom is considered to be reduced because its oxidation state decreases from 0 in elemental carbon to -4 in methane.

Even though the C-H bonds in methane are nonpolar, the concept of electronegativity still helps explain the distribution of electron density within the molecule. Carbon has an electronegativity of 2.5 and hydrogen has an electronegativity of 2.1. The slight difference in electronegativity leads to a slightly uneven sharing of electrons, which is relevant when considering the oxidation states in the compound.

The formation of covalent bonds involves the sharing of electrons and not the complete transfer of electrons. However, for the purpose of identifying redox reactions in covalent compounds, we assign oxidation states based on electronegativity differences and the hypothetical distribution of electrons. Thus, when hydrogen forms a bond with a more electronegative atom like carbon, it is considered to have an increased oxidation state, reflecting a hypothetical loss of electron control, which fits the definition of oxidation.