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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Maradona on November 14, 2005, 06:45:53 PM

Title: molecular shapes
Post by: Maradona on November 14, 2005, 06:45:53 PM

Hellow, How do u tell what molecular shape a bond is, like linear, tetra etc..

for H2O for example i know how to draw it but i cant seem to figure out what shape it is

Title: Re:molecular shapes
Post by: Donaldson Tan on November 14, 2005, 07:49:14 PM

google for VSEPR Theory..

This link might help.
http://www.chemicalforums.com/index.php?board=2;action=display;threadid=3251;start=msg13792 (http://www.chemicalforums.com/index.php?board=2;action=display;threadid=3251;start=msg13792)

Title: Re:molecular shapes
Post by: mike on November 14, 2005, 07:49:55 PM

You must use the VSEPR theory (Valence Shell Electron Pair Repulsion). The interactions in order of repulsion (greatest to smallest) are:

lone pair - lone pair
lone pair - bonding pair
bonding pair - bonding pair

In general the molecule will take the shape that causes least interactions. Usually your choices are:

linear
V-shaped
trigonal planar
tetrahedral
pyramidal

I am presuming you can draw the dot structure for water (H2O). If you left it as a linear molecule you will notice that there is 90 degrees between the lone pairs and bonding pairs etc. A kind of tetrahedral arrangement of the lone pairs and bonding pairs around the O will produce a greater distance (105ish) which results in a V-shape for H2O molecule.

Title: Re:molecular shapes
Post by: AWK on November 22, 2005, 02:41:53 AM

http://www.cat.cc.md.us/~cminnier/121/lewis/121hybridlecture.htm