Electronegativity and the Polar Bond
Unequal attraction for shared electrons gives a bond partial positive and negative charges. The strengths and directions of the bond dipoles determine whether their combined effect leaves the molecule polar.
What a learner can do afterwards
- Use a periodic trend to say which of two atoms pulls the shared pair harder
- Mark partial charges on a bond and explain what the symbols mean
- Decide whether a molecule is polar overall, given both its bond polarities and its shape
1 · Read
Electronegativity measures how strongly an atom attracts shared electrons. In H2, equal attraction gives an even electron distribution and a nonpolar bond. In H-Cl, the distribution shifts toward chlorine. Chlorine has a partial negative charge (delta minus); hydrogen has a partial positive charge (delta plus). These are not full ion charges. Electronegativity generally increases up a group and to the right across a period. Fluorine has the highest value.
An electronegativity difference is a rough guide to bond type, not a fixed cutoff. H-Cl differs by 0.9 and H-F by 1.9; both share electrons unequally in polar covalent bonds. Sodium chloride, with a difference of 2.1, is ionic: attraction holds Na+ and Cl- ions together. Electron transfer can form these ions. A zero or tiny difference suggests nonpolar covalent bonding. Consider the elements too: two nonmetals usually share; a metal and a nonmetal often form ions.
Each C-O bond in carbon dioxide is polar toward oxygen. CO2 is linear, so its two equal bond dipoles point in opposite directions and cancel. Water is bent, so its O-H dipoles combine to give an overall dipole. A molecule is polar when the combined dipole is nonzero. Two opposite dipoles cancel only if they are equal. Being straight or having some symmetry is not enough on its own.
When you meet a new molecule, work in three steps. First sketch its shape: straight, bent, or something else. Then draw each bond pull as an arrow toward the stronger puller. Last, add the arrows: opposite equal arrows cancel, angled arrows combine. Try it on an N-H bond: the trend says nitrogen pulls harder than hydrogen, so nitrogen gets delta minus.
Unequal sharing makes polar bonds. Molecular polarity depends on both bond-dipole strengths and the directions set by the molecule's shape.
Five original readings were written for this dataset using textbook and how-to records as factual background. The retained media is TED-Ed's "How atoms bond - George Zaidan and Charles Morton", credited to George Zaidan and Charles Morton through the hoofer-content talks record. The flashcards draw on imported facts-collection material, with corrections to scientific qualifications. The linked video's reuse license is not established by the supplied record.
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