chapter 9 notes – part iii mr nelson 2010. polarity but just because a molecule possesses polar...

Chapter 9 Notes – Part III

Mr Nelson 2010

Polarity

• But just because a molecule possesses polar bonds does not mean the molecule as a whole will be polar.

Polarity

• There are two ways to tell if a molecule is nonpolar:– Symmetry – perfect symmetry

= nonpolar

– Dipoles moments – if the dipoles ‘cancel out’ the molecule is nonpolar

Examples

• Draw the Lewis Dot Structure for:– HCl

– CCl4

Bonding & Lone Pairs

• Electron pairs that are shared are called bonding pairs

• Electron pairs that are not bonded or shared are called lone or unshared pairs

Steric Number• The total electron pairs

around the central atom is the steric number.

• Double or triple bonds count as one steric number (electron domain).

• The central atom has a steric number of four.

Determining the shape of molecules

VSEPR (not the Bond girl Vesper)

• VSEPR: Valence Shell Electron Pair Repulsion

– Electron pairs will arrange so they are as far apart as possible. ALL HAVE NEGATIVE CHARGES

– ALL e- pairs determine the shape, bonded or not, but ONLY bonded pairs determine the name of the shape.