In a compound, which element is assigned the negative oxidation number due to electronegativity?

• A. The less electronegative element
• B. The more electronegative element gets the positive sign
• C. The more electronegative element gets the negative sign
• D. All oxidation numbers are the same

Answer: (C)

When assigning oxidation numbers, the key idea is that electrons are not always shared equally in a bond. The atom that is more electronegative attracts the bonding electrons more strongly, so it is treated as gaining electron density. That atom is given a negative oxidation number, while the less electronegative atom is treated as losing electron density and is given a positive oxidation number. The total of all oxidation numbers in a neutral compound must be zero, which aligns with this distribution. For example, in water, oxygen is more electronegative than hydrogen, so oxygen gets -2 and each hydrogen gets +1. In sodium chloride, chlorine is more electronegative than sodium, so chlorine is -1 and sodium is +1. Thus, the element with higher electronegativity is assigned the negative oxidation number.