Electronegativity Approach to Chemical Bonding

Electronegativity approach to chemical bonding Electronegativity - the ability of an atom to attract electrons to itself in a covalent bond. Have you ever wondered why are some some bonds are ionic or covalent when it should be otherwise? Such as those of Al2Cl2 or BeCl2 ?

Think of this: 1) In non-polar covalent molecules: Electrons are equally shared 2) In polar covalent molecules: Electrons are shared, but are attracted to an atom more 3) In ionic molecules: Electons are no longer shared, instead, it was transferred from an atom to another

In another perspective What 1) 2) 3)

if: ALL atoms tend to attract electrons to them Each have a varying strength to attract electrons When two atoms of same strength are bonded, they cannot “out-attract” each other, they share the electrons equally. 4) When two atoms of slightly different strength are bonded, one will “out-attact” the other, the electrons are closer to one of the atoms. 5) When two atoms of big differece in strength are bonded, one will totally rip the electrons off from the other, the atoms of greater attraction gets to keep all the electrons. 6) This how electronegativity tells you whether the bonds are ionic or covalent (and if its polar)

Electronegativity are values assigned to elements based on their relative ability to attract electron to themselves in a covalent bond. The values may differ from source to source. Below is a chart to show the general trend of the electronegativity values of elements. As you can see, Fluorine, Oxygen and Nitrogen are most electronegative elements. (Thus giving rise to hydrogen bonds when covalently bonded to Hydrogen atoms)

As a general rule of thumb: Electronegativity difference

Type of bond

Greater than 2

Ionic

Between 0 to 2

Covalent (Polar)

0

Covalent (Non-polar)

*Do take note that if the polarity of the bond is different from that of the entire molecule! *Also note that the value of 2 here is just a general guideline, there is no clear line drawn here. Values ranging between 1.7 to 2.1 can be in the grey zone.

Back to: In Al2Cl2, difference in electronegativity = 1.5, thus the molecule is covalent In BeCl2 , difference in electronegativity = 1.5, thus the molecule is covalent