When bonded atoms do not attract electrons equally, electron density shifts. The bond becomes polarized: one end carries more negative character and the other more positive character.
The essential idea
When bonded atoms do not attract electrons equally, electron density shifts. The bond becomes polarized: one end carries more negative character and the other more positive character.
Example
In H–Cl, chlorine attracts electron density more strongly than hydrogen. The bond is polar without requiring a complete electron transfer.
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Mini problem
Why is H₂ nonpolar?
Show the solution
Because the atoms are identical and attract electron density equally.
Common mistake
Do not replace reasoning with a memorized rule. Always check geometry, units, coefficients or model assumptions.
Guided exercise
Rank H–H, H–Cl and Na–Cl from least polarized to most polarized.
Show the detailed solution
H–H is nonpolar. H–Cl is polar. Na–Cl has much stronger ionic character. The ranking uses electronegativity difference and the chosen bonding model.
Avoid this
Caution: an electronegativity difference does not create a universal sharp boundary between 'covalent' and 'ionic'.
It compares how strongly a bonded atom attracts the bond’s electron density. Partial charges δ⁺ and δ⁻ are not full ionic charges.
Key idea
Bond polarity
Key idea
Bond polarity
Explained answer. A good answer should restate the central idea in your own words and apply it to a concrete case. Check what changes, what stays constant, and which quantity supports the conclusion.
Guided example
Bond polarity
Explained answer. A good answer should restate the central idea in your own words and apply it to a concrete case. Check what changes, what stays constant, and which quantity supports the conclusion.
Put it into practice
Bond polarity
Choose a concrete case linked to Bond polarity. Write down the known information, what you are trying to find, and the units. Then state the rule, model or trend you will use. If a calculation is involved, keep the units visible at every line; if it is conceptual, state what changes and what remains fixed.
Check your answer
A strong answer contains four things: the starting situation, the variable that changes, the direction or numerical result, and one check. The check can be a unit, an order of magnitude, a limiting case or a comparison with a familiar example.