## Definition and distinguishing

Melissa Villanueva1K
Posts: 64
Joined: Wed Nov 15, 2017 3:01 am

### Definition and distinguishing

Could someone tell me what sigma and pi bonds are? As well as how to determine if a bond is a sigma or a pi bond. An example would really help, thanks!

klarratt2
Posts: 60
Joined: Fri Sep 28, 2018 12:16 am

### Re: Definition and distinguishing

A single bond is a sigma bond. A double bond is a sigma bond plus a pi bond. A triple bond is one sigma and two pi bonds.

A sigma bond is a basic covalent bond, with the bond in line with the bonding orbitals. You can only ever have one sigma bond between any two atoms.

A pi bond is a covalent bond between orbitals perpendicular to the bond direction, usually p-orbitals (never s). The resulting bond is roughly shaped like two croissants with the tips touching at the bonded atoms. Pi bonds do not allow rotation around the bonding axis due to this geometry.

A second pi bond (the third bond in a triple bond, or a second double bond to another atom) is always perpendicular (orthogonal) to the first one. In other words, if the sigma bond is on the x axis, one pi bond will form between orbitals on the y axis and another will form between orbitals on the z axis.

Beatrice Petelo 1F
Posts: 62
Joined: Fri Sep 28, 2018 12:17 am

### Re: Definition and distinguishing

Bonds form between two atoms when:
1. orbital on one atom occupies the same region of space as an orbital on the other atom. When this occurs, the two orbitals overlap.
2. total # of electrons in both orbitals is no more than two

sigma bonds: two atomic orbitals overlap head-to-head
- These are cylindrically symmetric about the bond axis (z-axis)
- example: overlap of 1s orbitals

pi bonds: two atomic orbitals overlap when parallel
-The electron distribution is above and below the bond axis (z-axis)
example: overlap of 2p orbitals

Here is a link for a visual of the overlaps: https://www.chegg.com/homework-help/def ... pi-bonds-6

Kelly Zhang 1L
Posts: 31
Joined: Fri Sep 28, 2018 12:18 am

### Re: Definition and distinguishing

Does the orientation or shape of molecules affect the length of its bonds?