CHEMISTRY COMMUNITY

How can you tell the shape of the molecule from the Lewis Structure?

Why is Hydrogen bond shape not 90 degrees but 109 degrees I didn't understand that part.

Anjali_Kumar3E wrote:Why is Hydrogen bond shape not 90 degrees but 109 degrees I didn't understand that part.

This is because in reality, molecules exist in 3 dimension, not 2. So in 3D, a molecule such as CH4 will try to maximize the distance between each bond, which will lead it to have 109.5 degrees between each bond rather than 90 degrees. If you were strictly looking at the shape in 2 dimension, it would be 90 degrees.

Lewis structures are a good starting point in finding the 3-D structure of a molecule, because they help us find an approximate location of binding e- and lone pair e-, which is what we need to determine the shape of a molecule (for example, if it's bent(H20) or linear (CO2)).

VSEPR also gives you structures based on experimentally observed results. Hence, the rules outlined in VSEPR will allow you to essentially represent structures in a 2-D manner.

VSPER allows you to tell the shape of the structure

Using the Lewis structure, you can see how many electron pairs and lone electron pairs there are. From that you can write the VSEPR equation in the form AX_nE_n. From the VSEPR equation, you can refer to a chart for the molecular shape

From the lewis structure we can identify the number of lone pair and bonded electrons and from this we could classify the molecule to a shape.

Do we have to know how to draw each molecular shape for the test or are we just going to be identifying them?