SMALL MOLECULES

Mercury

Federal Panel Hears Testimony on Vaccinations and Autism

E.P.A. Raises Estimate of Babies Affected by Mercury Exposure

Researchers Retract a Study Linking Autism to Vaccination

Minamata disease

photo by Eugene Smith

Dartmouth
Professor's
Accident

Lead

Lead is confirmed as source of Beethoven's illness

Li, Na, K

Salt Disolving (from UAkron)

Nerves

CO

Carbon Monoxide From Heater Kills Georgia Premier

Glycolysis

BONDING

MIT orbitals

bonding contours prepared by William F. Coleman.

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.

abbreviated periodic chart

H							He
Li	Be	B	C	N	O	F	Ne
Na	Mg	Al	Si	P	S	Cl	Ar
K	Ca	Ga	Ge	As	Se	Br	Kr

_________________________>
decreasing size
_________________________>
increasing 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

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

** 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.

Na K Mg anc Ca usually form salt structures when they are not disolved as ions.

Carbon

Paul Reisberg preisberg@wellesley.edu
Chemistry Department
Date Created: September 3,1998
Last Modified:Febr 3, 2006
Expires: August 30, 2008