Electronegativity and Polarity

1. Electronegativity and Polarity

2. Elecronegativity • Relative ability of an atom to attract electrons in a chemical bond • Fluorine has the highest electronegativity value • Trend: • Increases across (left to right) a period • Decreases down a group

3. Types of covalent bonds • Non-polar covalent: equal sharing of electrons • Polar covalent: unequal sharing of electrons

4. Non-polar covalent • Sharing of electrons equally • Usually occurs when two identical atoms are bonded together. • Examples: H2, O2, N2, Cl2, Br2, I2, F2

5. Polar covalent • Unequal sharing of electrons • Unequal sharing caused by 2 elements with different electronegativities (different abilities to attract electrons). • The bond is called a dipole (two poles) • Creates molecule with partial charges

6. Partial charges symbolized by (delta) + and - • The more electronegative atom is located at the partially negative end • Example: + - H-Cl and H-Cl

7. Polar molecule or not? • The shape of a molecule usually tells if a molecule is polar or not • If the VSEPR shape is symmetric it is usually non-polar • If the molecule is asymmetric it is polar

8. Youtube polar vs nonpolar

9. Intermolecular Forces • The force that exists between separate molecules. • This force attracts molecules to each other.

10. 3 Types • London Dispersion force or induced dipole moment between molecules; only force in non-polar molecules; weakest force (caused by the motion of electrons) (ex: CH4) Induced dipole moment

11. Dipole-dipole the force between two polar molecules; stronger force (ex: HCl)

12. Hydrogen bond forms between the hydrogen end of one dipole and fluorine, oxygen, or nitrogen (that have at least one lone pair) end of another dipole; strongest force (ex: H2O) Hydrogen bond

13. IMF’s • ALL molecules have dispersion forces • All polar molecules have dipole-dipole forces and dispersion forces • Molecules that hydrogen bond have all 3

14. Solubility of polar molecules • Properties are due to intermolecular forces • Like dissolves like • Polar substances will dissolve polar molecules (and ionic compounds) • Non-polar substances will dissolve non-polar molecules