Let's learn about electronegativity in A-Level Chemistry and see how it affects bonding!
Electronegativity is the ability to attract the bonding electrons in a covalent bond
Atoms with strong electron pulling power in covalent bonds are said to be highly electronegative.
Fluorine is the most electronegative element. Oxygen, nitrogen chlorine are also strongly electronegative.
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/4979856/579397_298133.jpeg)
In a covalent bond between two atoms of different electronegativities, the bonding electrons are pulled
towards the more electronegative atom. This makes the bond polar.
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/4979856/5064_710036.png)
The covalent bonds in diatomic elements are non-polar because the atoms have equal electronegativities. Electrons are equally attracted to both nuclei.
In a polar bond the difference in electronegativity between the two atoms causes a dipole.
A dipole is a difference in charge between the two atoms causes by a shift in electron density in the bond.
The greater the difference in electronegativity between two atoms, the more polar the bond will be.
Shape and polarity
Whether a molecule has a permanent dipole depends on its shape and the polarity of its bonds.
1. In a simple molecule, like hydrogen bromide, the polar bond gives the whole molecule a permanent dipole –it’s a polar molecule.
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/4979856/641203_854918.png)
2. A more complicated molecule may have several polar bonds. If the polar bonds are arranged so they point in opposite directions, they’ll cancel each other out. The molecule is non-polar overall.
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/4979856/336437_190011.jpeg)
3. If the polar bonds all point in roughly the same direction, then the molecule is polar
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/4979856/656258_965958.png)
4. Lone pairs of electrons on the central atom also have an effect on the overall polarity and may cancel out the dipole created by the bonding pairs.
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/4979856/190681_937413.jpeg)
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/4979856/872629_335293.jpeg)
Drafted by Eunice (Chemistry)
References
https://chem.libretexts.org/Courses/Oregon_Institute_of_Technology/OIT%3A_CHE_202_-_General_Chemistry_II/Unit_5%3A_The_Strength_and_Shape_of_Covalent_Bonds/5.2%3A_Molecular_Shape
http://biochemhelp.com/how-to-predict-polarity-of-molecules-based-on-their-shape.html