In some covalent bonds, one of the two atoms holds electrons more tightly ⇒ polar covalent bond results between two atoms
Delta (δ) Notation for polar bonds • Electrons concentrate around the more EN atom in a molecule ⇒ Atom gains a partial negative charge, indicated with δ– • Since electrons spend less time around the other atom ⇒ Other atom gains a partial positive charge, indicated with δ+
For you to try… • For each of the bonds to the right: • i. Use delta notation (δ+ and δ–) to indicate which atom in each bond is more electronegative, and • ii. Use an arrow to point from the less electronegative atom to the more electronegative atom.
POLARITY OF MOLECULES • For diatomic molecules: • – nonpolar molecules: when the 2 atoms have equal EN values • – polar molecules: when the 2 atoms have different EN values – have dipole (+ and – ends)
For molecules of three or more atoms • – polarity depend on the individual bonds and geometry around central atom • – Polar molecules have an overall dipole (positive end and negative end) • – In nonpolar molecules, there may be individual dipoles that cancel → no overall dipole
Guidelines for Determining if a Molecule is Polar or Nonpolar or Ionic • Use the electronegativity (EN) chart and compare the change in EN. • 0-.4 nonpolar covalent • .4 -1.7 polar covalent • Above 1.7 ionic
You try it… • Draw the covalent molecules on the right. Label the following: • δ– and δ+ • Arrows toward δ– • Change in EN • Nonpolar covalent, polar covalent, or ionic