Bonds are polar when the difference in electronegativity of atoms is greater than 1.7, with one atom drawing electrons toward itself.

Here's why:

* Electronegativity: This is a measure of an atom's ability to attract electrons in a bond. Atoms with higher electronegativity will pull electrons closer to themselves.

* Polar Bonds: When there is a significant difference in electronegativity between two atoms, the electrons are not shared equally. This creates a partial positive charge on the less electronegative atom and a partial negative charge on the more electronegative atom.

* The 1.7 Threshold: While the 1.7 value is a commonly cited guideline, it's important to understand that it's not a strict cutoff. Some sources use slightly different values. The key point is that a larger difference in electronegativity leads to a more polar bond.

Example:

In a water molecule (H₂O), oxygen has a higher electronegativity than hydrogen. This creates a polar bond, with oxygen having a partial negative charge (δ-) and each hydrogen having a partial positive charge (δ+).

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