Question

How do you determine the number of pi and sigma bonds in a structure and locate them?

Answer 1

Using extended structure models

Explanation:

https://socratic.org/questions/what-is-the-difference-between-a-condensed-structural-formula-and-a-structural-f

Here you have a more in-depth analysis of structure formulas.

Start off by writing down the respective compund using the extended structure model. Each simple covalent bond (represented by the line between 2 atoms) will be a sigma bond ;

Any other different from that ( double , triple covalent bonds ) will still have one sigma bond, the rest of the lines being counted as pi bonds

I'll give you an example:

Let's take the propane extended structure formula (which i stole from the answer above):

It is a saturated compound, so you will only have simple ( sigma ) covalent bonds - there are no pi bonds. Also, in this particular case ( for saturated aliphatic alkanes ) you can use a formula:

number of sigma bonds = number of atoms - 1 (which you can determine using the molecular formula )

If you would use that formula for propane, number of sigma bonds will be 3 + 8 - 1 = 10, as shown above.