Bonds and Electronegativity

Bonding:
Previous studies in chemistry have shown us three main types of bonds.

• Ionic bonds which exist between a metal and a non-metal. In this bond the electrons are transferred. 
• Covalent bonds which exist between a non-metal and a non-metal. In this bond the electrons are shared.  
• Metallic bonds which exist between metals and metals. In this bond pure metals are held together by electrostatic attraction.

We have worked largely with covalent and ionic bonds and know them to be illustrated as such:

 

Electronegativity: 

An atom's electronegativity reflects its ability to attract electrons in a chemical bond. As we learned before, there is a distinct trend in the periodic table when reading for the electronegativity of an element: 

 

And the values are as follows:  

From these two tables we can conclude that fluorine is the most electronegative element with an electronegativity of 4.0 whereas caesium and francium are the least electronegative elements with an a shared electronegativity of 0.7. And these values are useful as they help us distinguish between ionic and covalent bonds as well as the sub-bonds of a covalent bond. These two sub-bonds are: 

• Polar covalent bonds which form an uneven sharing of electrons 
• Non-polar covalent bonds which form an equal sharing of electrons. 

By calculating the difference in electronegativity between the elements involved in a bond, we can predict the type of bond. The results are held within these ranges: 

• en > 1.7 = ionic bond; the electrons are transferred 
• en < 1.7 = polar covalent bond; the electrons are shared, but not equally
• en = 1.7 = non-polar covalent bond; the electrons are equally shared 

Examples: 

Predict the type of bonds formed by calculating the electronegative difference in the following compounds: 

• H-O
• Electronegative Difference: 3.44 - 2.20 = 1.24
• Type of Bond: Polar Covalent Bond
• C-H  
• Electronegative Difference: 2.55 - 2.20 = 0.35
• Type of Bond: Polar Covalent Bond
• K-F  
• Electronegative Difference: 3.98 - 0.82 = 3.16  
• Type of Bond: Ionic Bond
• N-H  
• Electronegative Difference: 3.04 - 2.20 = 0.84 
• Type of Bond: Polar Covalent Bond
• Na-F  
• Electronegative Difference: 3.98 - 0.93 = 3.05  
• Type of Bond: Ionic Bond
• O-Cl 
• Electronegative Difference: 3.44 - 3.16 = 0.28  
• Type of Bond: Polar Covalent Bond 
• O-O 
• Electronegative Difference: 3.44 - 3.44 = 0.00 
• Type of Bond: Non-Polar Covalent Bond  

Further explanation on this topic can be found with the following videos, one focused on the electronegativity trend and other deals with distinguishing the bonds:

 

- George Spencer, Simon Sierra, and Benedict Suratos