Introduction to Electronegativity

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Electronegativity Scale

An Electronegativity Scale depicted by a graduated vertical line with values 3.5, 3.0, 2.5 and 2.1 from top to bottom respectively on the left. A red sphere labeled 'O' representing an oxygen atom is adjacent to 3.5, a blue sphere labeled 'N' representing a nitrogen atom is adjacent to 3.0, a dark grey sphere labeled 'C' representing a carbon atom is adjacent to 2.5 and a small light grey sphere labeled 'H' representing a hydrogen atom is adjacent to 2.1.

Polar Covalent Bond

An animation of the Polar Covalent Bond depicted by the red sphere and the light grey sphere arranged in a top-bottom manner is at the right. An oval-shaped purple shading region is shown with tips in the top-bottom orientation wherein a hydrogen atom is present inside its bottom tip region while an oxygen atom is just above the top tip. Inside the oval area, a pair of smaller yellow spheres with minus signs moves randomly but predominantly in the region closer to the oxygen atom. δ Superscript minus is at the top of the oxygen atom and δ Superscript plus is below the hydrogen atom.

An atom's tendency to attract electrons is called electronegativity. Atoms near the top of the scale attract electrons more strongly than atoms near the bottom. For instance, when O and H form a bond, O pulls electrons towards itself, creating a partial negative charge. This leaves the H with a partial positive charge. The result is a polar covalent bond.