Covalent Bonding and Molecular Compounds

6.2

Molecules

Molecules – a neutral group of atoms held together by covalent bonds

Molecular compound – a cmpd whose simplest units are molecules

Chemical formula – indicates relative # of atoms of each kind in a chemical compound by using atomic symbols & subscripts

Molecules

Molecular formula – shows types & # of atoms combined in a single molecule of a molecular compound

Diatomic molecule – a molecule with only 2 atoms.

Energy change in covalent bond formation

Bond will form when potential energy will be at lowest.

Nature favors situations when E can be reduced

Energy change in H2

Formation of a bond

Bond length – the average distance b/t 2 bonded atoms at their lowest potential energy

Bond energy – the E required to break a chemical bond and form neutral isolated atoms

The Octet Rule Atoms want 8 e- in their

valence shell There are exceptions like H,

He, and B

Electron Dot notation

EDN – an e-config notation in which only the valence e-are shown as dots around an elements symbol

What is the dot notation for F, Na, Al, Kr

Lewis Structures L-S – atomic symbol is nuclei and

inner shell e-’s and dot pairs and dashes b/t atoms represent e-pairs in covalent bonds or unshared pairs

Structural formula – indicates kind, #, & arrangement of bonds but not the unshared pairs of e-’s

Rules for drawing LS for multiple ion compounds

1. H and halogens often bind to 1 other atom and are usually on the outside or end of a molec.

2. Atom with lowest e-neg is often central. They have less than 7 e- and can form more than 1 bond.

Rules for drawing LS for multiple ion compounds

3. When placing valence e-, put 1 e- on each side b4 pairing e-

Lewis Structures

Single Bond – covalent bond where 1 pair of e-’s are shared b/t 2 atoms

Draw the Lewis structure for … H2 HF NaCl

CH4 CH3I

How to draw LS for more complex molecules

1. Draw the LS for each element

2. Put least electronegative element in center

3. Arrange other elements around central atom to satisfy octet (H only needs 2)

4. Change dots to lines to show bonds b/t atoms

How to draw LS for more complex molecules

5. For unpaired electrons, try to form multiple bonds.6. If octets are still not satisfied, try to move electrons around molecule.

Multiple Covalent Bonds

Double bond– 2 pairs of e-’s(4e-) Triple Bond – 3 pairs of e-’s (6e-) What is the Lewis structure for …O2 N2 CO2

CH2O C2HCl

Resonance Structures

R.S. bonding in molecule or ions that can’t be represented by a single Lewis Structure

O3

Delocalized – e- shared b/t more than 2 atoms

Ions

Complete the Lewis Structures for the following…

NH4+ OH-

CN- NO2_