Unit 6 Notes – Part II

Mr Nelson 2010

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 as the steric number.

• Double or Triple bonds count as 1 steric number.

• The central atom in this molecule, A, has a steric number of four.

Determining the shape of molecules

• Electrons, whether they be bonding or lone pairs, repel each other.

• By assuming the electron pairs are placed as far as possible from each other, we can predict the shape of the molecule.

VSEPR

• 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.

Molecular Shapes

• The shape of a molecule plays an important role in its reactivity.

• By noting the number of bonding and lone pairs we can easily predict the shape of the molecule.

Different Bond Types

• Ionic (extremely polar)– Electrons are transferred

• Covalent– Polar – uneven sharing of electrons– Nonpolar – even sharing of electrons

Nonpolar Covalent Bonds

Polar Covalent Bonds

Ionic Bonds

Nonpolar, polar, and ionic bonds

• (a) – a nonpolar covalent bond

• (b) – a polar covalent bond

• (c) – an ionic bond

Electronegativity• Electronegativity is the ability of atoms in a molecule

to attract electrons to themselves.

• On the PT, EN increases:– …from left to right across a row.

• EN decreases– …from the top to bottom of a group (column).

Bond Properties and Electronegativity

Bond properties and electronegativity

• Any bond can be classified by subtracting the EN of the 2 elements involved

Polar Covalent Bonds

• Electrons are not always shared equally in compounds.

• Oxygen pulls harder on the electrons it shares with hydrogen than hydrogen does.

• Oxygen’s end of the molecule has more electron density than the hydrogen end.