Chemistry - Electronegativity

 

- Info:

- This tutorial is based in http://www.chemguide.co.uk/basicorg/bonding/eneg.html#top.

 

- Example:

- Polar bond will be explaind on the carbon-flourine molecule shown in the following image.

 

 

- Polar bond can be understood by calculatin resulting electrical force by which each atom is attracting shared electrons.

- We can assume that in each atom electrical force generated by two electrons in lowest shell is canceld out by two protons from the nucleus.

† - By removing those electrons and protons from the picture we get:

- If all 3 carbon electrons would be located in nucleus their electrical force would be canceled out by three protons.

- We would be left with one proton on the left side attracting shared electrons.

- If all 6 flourine electrons would be located in nucleus their electrical force would be canceld out by 6 protons.

- We would be left with one proton on the leright side attracting shared electrons.

- This way both atoms would be attracting shared electrons with the same force† and we wouldn't have polar bond.

 

- Four protons from carbon nucleus attract each of the shared electrons with the force of FC:

- Seven protons from flourin nucleus attract each of the shared electrons with the force of FF:

 

FPC = 4kq2/r2

 

FPF = 7kq2/r2

 

- Electron e1 attracts each of the shared electrons with the force of Fe1:

 

Fe1 = kq2/(4r2)

 

- Each e2 electron attracts each of the shared electrons with the force of FC2:

 

Fe2 = kq2/(2r2)

 

- Vertical components of e2 cancel each other while horizontal componets add up.

- Horizontal component of e2 labeled as F2e2H is:

 

F2e2 = F2e2H + F2e2H = 2F2e2H

 

Fe2 = ÷2Fe2H

 

Fe2H = Fe2/÷2

 

Fe2H = kq2/(2r2÷2)

 

- So total horizontal influence from both e2 electrons is:

 

2Fe2H = kq2/(r2÷2)

 

- Now we can calculate resulting force of each atom to each of the shared electrons.

- Carbon atom attracts each of the shared electrons with the resulting force of:

 

FC = FPC - Fe1 - 2Fe2H = 4kq2/r2 - kq2/(4r2) - kq2/(r2÷2) = (kq2/r2) (4-1/4-1/÷2) = (kq2/r2) (4-1.66)

 

FC = 2.336 (kq2/r2)

 

- Fluor atom attracts each of the shared electrons with the resulting force of:

 

FF = FPF - 2Fe1 - 22Fe2H = 7kq2/r2 - 2kq2/(4r2) - 2kq2/(r2÷2) = (kq2/r2) (7-2/4-2/÷2) = (kq2/r2) (7-21.66) = (kq2/r2) (7-3.32)

 

FF = 3,68 (kq2/r2)

 

- Since shared electrons feel greater attracting force from flour atom then from carbon atom they will be spending more

† ††time around flour atom.

- But being closer also means that they are closes to the flour's electrones which means that from time to time repulsive

† ††force of those electrons will be dominant forcing shared electron to orbit around carbon atom for a while.

- This explanaation is simplified one since the acctuall explanation would involve quantum mechanics.