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# Molecular geometry of atoms

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I have this question:

Draw the Lewis dot structures of the following molecules and then predict their
geometry.
Indicate molecular geometry of the atoms and the position of lone pairs.
a. BeF2
b. BF3
c. CH 4
d. NH3
e. H2O

I am OK with the Lewis dot structures part, but what does "the indicate molecular geometry of the atoms" mean? How do I do it?

https://brainmass.com/chemistry/bonding/molecular-geometry-atoms-396016

## SOLUTION This solution is FREE courtesy of BrainMass!

Molecule geometry is essentially the shape of each molecule. This depends on how many atoms are bonded to the central atom and how many lone pairs of electrons there are. Regardless, there are only a few basic shapes to know because the objects attached to the central atom are always trying to be as far from the others as possible.

If there are two objects (atoms or lone pairs) coming off the central atom, they will make a linear shape.

If there are three objects, they will make a flat, triangular shape.

If there are four objects, they will make a shape like a tripod (this is called tetrahedral).

Using these basic shapes, you can remove points in the shape if there are lone pairs in order to get new shapes. I will explain this as we go.

BeF2 has no lone pairs and two objects (F) attached to the central Be. The molecular geometry will be linear.

BF3 has no lone pairs and three objects (F) attached to the central B. The molecular geometry will be the flat triangular shape, known in chemistry as "trigonal planar."

CH4 has no lone pairs and four objects (H) attached to the central C. The molecular geometry will be the tripod shape, known in chemistry as "tetrahedral."

NH3 has 1 lone pair and 3 objects (H) attached to the central N. This means there are 4 objects to start with, giving the tetrahedral shape. Because the lone pair doesn't actually take up any space, we can remove the top of the tetrahedron. Imagine removing the top of the tripod to have just the three legs and the base, forming a pyramid shape. This is known as "trigonal pyramidal."

H2O has 2 lone pairs and 2 objects (H) attached to the central O. Again, this would be the tetrahedral shape, but this time remove one of the legs of the tripod as well. You end up with a "bent" shape.

A lot of these shapes are complicated to visualize, so here is a good website: http://intro.chem.okstate.edu/1314f00/lecture/chapter10/vsepr.html
You can click on the links for the shapes for a 3D image of each.

Please let me know if you need any clarification!

This content was COPIED from BrainMass.com - View the original, and get the already-completed solution here!