Question

Why is water considered to be electronegative?

Answer 1

It's not. Molecules are never considered electronegative. Electronegativity is attributed to atoms, and atoms only. Polarity is attributed to molecules.

Water is polar because the electronegativity of oxygen (`~3.5`) is substantially greater than that of hydrogen (`~2.1`). Hence, the electrons within the molecular orbitals of water tend to be distributed more of the time towards oxygen than towards the hydrogens.

Thus, more negative charges are near oxygen and more positive charges are near the hydrogens.

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Another way to say it is that the dipole moment vector is pointed through the `"O"-"H"` bonds in such a way that their vector projections add to give a net dipole moment vector that points through oxygen. i.e. The two `mu_"OH"` components add to give `mu_("H"_2"O")`: