Covalent Bonds

 

BONDING

prepared by William F. Coleman.

How to draw Lewis structures:

1. Draw the skeletal structure.
2. Count the total number of valence electrons.
3. Draw single bonds between atoms.
4. Complete octet on atoms until run out of electrons.
5. Use multiple bonds or rings if not enough electrons to complete octets.

Atomic personalities

• The increasing number of protons as one goes across the chart leads to greater attraction of the surrounding electrons.
• This leads to the decreasing size of the atoms.
• The greater nuclear charge plus smaller distance between electrons and protons results in a greater attraction for electrons going from left to right. Atoms on the left tend to lose electrons more easily and those towards the right tend to gain electrons.
• Electronegativity is a way of expressing the pull on electrons between atoms in a molecule. An atom with a higher electronegativity will generally pull negative charge from a neighbor with a lower electronegativity.

for our purposes:

symbol	name	CHIME color	typical bonds*	Electronegativity**
H	hydrogen	white	1	2.3
C	carbon	light grey	4	2.5
N	nitrogen	blue	3	3.0
O	oxygen	red	2	3.6
S	sulfer	yellow	2	2.6
P	phosphorous	orange	phosphate PO4	2.2
Na	sodium	blue	Na+ ionic	0.9
K	potassium		K+ ionic	0.8
Mg	magnesium		Mg++ ionic	1.3
Ca	calcium	dark grey	Ca++ ionic	1.0
Cl	chloride	green	Cl- ionic	3.0

* We can rationalize most of these in terms of filling shells i.e. trying to have the electronic structure of the noble gases

** It will be sufficient to just remember that Carbon and Hydrogen have roughly equal electronegativities, Nitrogen has a greater electronegativity than both C and H and Oxygen's electronegativity is greater still.

Small Molecules

CO

Carbon Monoxide From Heater Kills Georgia Premier

• Paul Reisberg preisberg@wellesley.edu
• Chemistry Department
• Date Created: September 3,1998
• Last Modified:Febr 3, 20010
• Expires: August 30, 2018