3
$\begingroup$

Can someone explain the following types of molecules and predict their structure and shape?

It will help my understanding if you could provide an example.

AX3E,AX5 and AX6

note that A = central atom and X = bonding atoms.

$\endgroup$
3
  • 1
    $\begingroup$ Welcome to Chemistry.SE! One way you help yourself get a better answer to your question is by giving it a more descriptive title. "Help predicting molecular geometry" is more helpful to the community than "Help me with this question". I have edited your title. If you don't like it, let me know. $\endgroup$
    – Ben Norris
    Mar 25 '13 at 11:34
  • $\begingroup$ The title is OK with me. $\endgroup$
    – tom
    Mar 25 '13 at 11:50
  • 1
    $\begingroup$ You should read this: en.wikipedia.org/wiki/VSEPR_theory $\endgroup$
    – permeakra
    Mar 26 '13 at 18:27
7
$\begingroup$

It will depend on the number of lone electron pairs as well.

For example: $BCl_3$ will be triangular planar as it has no lone electron pairs.

$NH_3$ however will be triangular based-pyramidal because there are 3 bonded pairs of electrons and one lone electron pair.

Basically, it comes down to the number of electron pairs (both bonded and unbonded) around the central atom.

  1. Two electron pairs - Linear

    enter image description here

  2. Three electron pairs - Triangular planar

    enter image description here

  3. Four electron pairs - Tetrahedral

    enter image description here

  4. Five electron pairs - Triangular based bi-pyramidal (it's like triangular planar, but with one on top and one below, or two triangular pyramids with their base stuck together)

    enter image description here

  5. Six electron pairs - Octahedral (Square based bi-pyramidal)

    enter image description here

Those geometries include the lone electron pairs. For the molecular geometry, you will then need to exclude the electron pair.

E.g. $H_2O$ : central atom O. O has 4 electron pairs: 2 bonded, 2 lone. The shape, including lone electron pairs is Tetrahedral. Ignore the lone pairs now, you will be left with a bent molecular geometry.

enter image description here

Blue is oxygen;
Yellow is hydrogen;
White/Grey are lone/unbonded electron pairs.

I hope this makes sense. :)

$\endgroup$
0
0
$\begingroup$

If you convert your equation to mol format or another format supported by OpenBabel you can use its tools to add 3D structure information to the files. Also if you need quality conformations you could use tools OpenEye's Omega or as I prefer Balloon which can quickly give biologically significant structures. Balloon works on many different atom types and most smiles Omega is parameterised for a select few smiles.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.