Strength of Chemical Bonds

 General Chemistry Index

Where are we going with this? This page will give the ability to use laboratory observations and data to compare and contrast ionic, covalent, network, metallic, polar, and non-polar substances with respect to constituent particles, strength of bonds, melting and boiling points, and conductivity; provide examples of each type.

Strength of Chemical Bonds / Bond Energy
Are all chemical bonds the same… 

Compounds are formed when two or more elements combine chemically in fixed, specific ratios. Combine… What?

Elements combine to form compounds by bonding to other elements—in fixed, specific ratios. They do this in several ways, both intramolecularly (strong) and intermolecularly (weaker).  (See also.)

Intramolecular bonds occur as either ionic or covalent (and some covalent bonds are polar).

When considering the strength of chemical bonds, it is convenient to rank bond strength by type of bond. However do thing this is a drastic over-simplification.

Aside from saying that intramolecular bonds are stronger than intermolecular bonds, we cannot say always this or that (it is chemistry, after all!).

"When a bond is strong, there is a higher bond energy because it takes more energy to break a strong bond" (Source, 2024). Thus, bond strength is actually a way of comparing bond energy. And bond energy is far from simple!

The following table shows the bond energy of various bonds:

Table 1: Average Bond Energies (kJ/mol)

Single Bonds						Multiple Bonds
H—H	432	N—H	391	I—I	149	C = C	614
H—F	565	N—N	160	I—Cl	208	C ≡ C	839
H—Cl	427	N—F	272	I—Br	175	O = O	495
H—Br	363	N—Cl	200			C = O*	745
H—I	295	N—Br	243	S—H	347	C ≡ O	1072
		N—O	201	S—F	327	N = O	607
C—H	413	O—H	467	S—Cl	253	N = N	418
C—C	347	O—O	146	S—Br	218	N ≡ N	941
C—N	305	O—F	190	S—S	266	C ≡ N	891
C—O	358	O—Cl	203			C = N	615
C—F	485	O—I	234	Si—Si	340
C—Cl	339			Si—H	393
C—Br	276	F—F	154	Si—C	360
C—I	240	F—Cl	253	Si—O	452
C—S	259	F—Br	237
		Cl—Cl	239
		Cl—Br	218
		Br—Br	193
*C == O(CO2) = 799

 (Source, 2024)

A cursory look will indicate that a lot of the ionic bonds are stronger than a lot of the single covalent bonds. But looking closer will reveal that not all ionic bonds are stronger than all covalent bonds, 

For instance, compare the Si-O bond (covalent) to the H-Cl (ionic) bond.

FURTHER, most of the double and triple covalent bonds are stronger (have higher bond energy) than most of the ionic bonds (c.f. C ≡ C ).

So what?

To rank bond strength by bond type proves to be a pretty bad idea. While there are tendencies, there is no all-fitting rule. In the end, the convenience of such an attempt must be sacrificed to accuracy.