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 easily 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.

• Paul Reisberg preisberg@wellesley.edu
• Chemistry Department
• Date Created: September 3,1998
• Last Modified:September 8, 1999
• Expires: August 30, 1999