Chemistry · Chemical Bonding · NEET
Electronegativity is the power of an atom to pull the shared pair of electrons in a covalent bond towards itself. Think of two people holding one rope (the electron pair). The stronger puller drags the rope to their side. Fluorine is the strongest puller (highest electronegativity), and the value drops as you go down or to the left in the periodic table. For NEET the order to remember is F > O > N > Cl. A bigger electronegativity of an atom means it holds bonding electrons more tightly.
Look at the two atoms joined by the bond. If they are the SAME element (H-H, Cl-Cl, O=O), their electronegativity is equal, the pull is balanced, and the bond is non-polar. If they are DIFFERENT elements (H-Cl, C-O, O-H), one atom pulls harder, so the electrons shift and the bond becomes polar. Rule: electronegativity difference = 0 means non-polar bond; any difference greater than 0 means a polar bond. This is why NEET loves diatomic molecules like N2 and Cl2 as non-polar examples.
In a polar bond the electrons sit closer to the more electronegative atom. That atom does not become a full ion, it just gets a small partial negative charge written as delta minus. The other atom gets a small partial positive charge written as delta plus. Example: in H-Cl, chlorine is delta minus and hydrogen is delta plus. These are partial (fractional) charges, not full +1 or -1. This partial charge is what creates the bond dipole you study later in dipole moment.
This is the biggest trap. Each individual C=O bond IS polar because carbon and oxygen have different electronegativity. But CO2 is a straight LINEAR molecule (O=C=O). The two bond pulls point in exactly opposite directions and are equal in size, so they cancel out completely. The result is a non-polar molecule with zero net dipole. Water (H2O) is different because it is bent, so its two O-H pulls do NOT cancel, and water stays polar. So bond polarity and molecule polarity are two different things, and shape decides the final answer.
Yes, for a single bond. The larger the electronegativity gap between the two atoms, the more the electrons shift, the larger the partial charges, and the more polar (more ionic character) the bond becomes. So H-F is more polar than H-Cl because the gap for H-F is bigger. If the difference gets very large (roughly greater than about 1.7 on the Pauling scale, like NaCl), the bond is counted as ionic instead of polar covalent. This is why electronegativity is the bridge between covalent and ionic bonding.
A polar BOND is about two atoms: it exists whenever the two joined atoms differ in electronegativity. A polar MOLECULE is about the whole shape: it exists only when the bond dipoles do not cancel. A molecule can have polar bonds but still be non-polar overall if it is symmetric (CO2, BF3, CCl4, CH4). A molecule is polar only when it is unsymmetrical (H2O, NH3, CHCl3). NEET questions on zero dipole moment are really testing this exact difference.
Which of the following molecules is non-polar in nature?
Which of the following set of molecules will have zero dipole moment?
The correct order of dipole moments for molecules NH3, H2S, CH4 and HF is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Fluorine has the highest electronegativity (about 4.0 on the Pauling scale). The common NEET order is F > O > N > Cl. Electronegativity increases across a period (left to right) and decreases down a group.
Yes. CO2, BF3, CCl4 and CH4 all have polar bonds but are non-polar molecules because their symmetric shapes make the bond dipoles cancel to zero net dipole.
As a rough NEET guide, a difference above about 1.7 on the Pauling scale gives a mostly ionic bond, while a smaller non-zero difference gives a polar covalent bond and a zero difference gives a non-polar covalent bond.
HCl is polar. Chlorine is more electronegative than hydrogen, so it pulls the shared electrons closer, giving Cl a partial negative (delta minus) charge and H a partial positive (delta plus) charge.
In NH3 the N-H bond dipoles and the nitrogen lone pair point the same way and add up. In NF3 the very electronegative F atoms pull the bond dipoles opposite to the lone-pair direction, so they partly cancel, giving NF3 a smaller dipole moment than NH3.
