Which atom in the pictured molecule will have the strongest partial positive charge?

Question

A ball-and-stick model of a molecule. The structure of the molecule, described from left to right, is four atoms attached to each other: one nitrogen, two carbons, and one oxygen. There are two hydrogen atoms attached to nitrogen, one hydrogen atom and one R group attached to the first (from left to right) carbon, one oxygen atom double-bonded to the second carbon, and one hydrogen atom attached to the oxygen atom.

The O atom that's in C=O.
The C that's in C=O.
The H that's bound to O.
The C that's bound to N.
The N atom.

This is the second-most positive atom in the molecule; it's bound to a highly electronegative O atom. But another atom is more positive. Which one?

Part C
Dr. Haxton says the O-O bond is polar and the C-C bond is nonpolar. A good student would say

Yes. O attracts electrons more strongly than C.
No, both bonds are highly polar.
No way. C is more electronegative than O.
Wrong again, Ralph. Both bonds are nonpolar.
Right! O is electronegative, so O2 is polar.

Answer 1

To determine which atom has the strongest partial positive charge in the described molecule, we should consider the electronegativity of the atoms involved and the structure:

1. Oxygen (O) is highly electronegative, so it pulls electron density towards itself when bonded with other atoms.
2. Nitrogen (N) is also relatively electronegative but less so than oxygen.
3. Carbon (C) has a lower electronegativity than both oxygen and nitrogen.
4. Hydrogen (H) is less electronegative than carbon.

Given these electronegativity differences, the strong electronegativity of the oxygen atom in the carbonyl group (C=O) pulls electron density away from the carbon (C) and the hydrogen (H) atoms. The carbon that is double-bonded to oxygen will carry a partial positive charge as it loses electron density to oxygen. The nitrogen atom, while also being connected to electronegative atoms, will be less positively charged than the carbon that's double-bonded to oxygen because both the carbon and nitrogen are closer to oxygen than the other atoms.

Considering these points, the atom that will have the strongest partial positive charge is the C that's in C=O.

For Part C: Dr. Haxton's comments on the polar bonds:

• O-O bond refers to the bond in molecular oxygen (O2), which is nonpolar because both atoms are the same and have equal electronegativity.
• C-C bond in general is also considered nonpolar because both carbon atoms have the same electronegativity.

However, if we consider a carbon that's bonded to more electronegative atoms (like in the described molecule), then that carbon could have polar character in such a context.

A good student would appropriately say: Yes. O attracts electrons more strongly than C. This reflects the understanding that the O-O bond is not polar, and typically, the general statement on C bonds as being nonpolar applies unless highly electronegative atoms are involved.