General Chemistry Review – Ionic and Covalent Bonding

The phenomenon of chemical bonding is a result of Coulomb's law, which governs the attraction and repulsion between charges. This law influences the properties of atoms and is responsible for electrostatic repulsion.

Atoms exchange electron pairs with one another. These associations are known as chemical bonds.

Electronegativity is a property of atoms that measures how strongly they attract electrons towards themselves.

When bonds are formed between atoms with different electronegativity, the electron pair in the bond is not shared equally. It will be polarised in the direction of the atom with the highest electronegativity. This implies that the more electronegative element will have a higher electron density (a net negative charge) than the less electronegative element (a net positive charge).

Polarisation increases as the difference in electronegativity increases.

Occasionally, the "sharing" of electrons to form a bond is only nominal. Suppose the parents of two boys, ages 10 and 8, give them a $20 bill "to share" and then leave. Assuming there is no further parental interference, what are the odds that the money will be divided evenly? I'm speaking from personal experience when I say that the odds are rather slim. Despite the fact that the two brothers are nominally sharing $20, the older brother has the ability to deliver an unbreakable Full Nelson and thus has the majority of purchasing power.

Likewise with atoms. At one end of the spectrum are the bonds between a highly electronegative element, such as fluorine, and a lowly electronegative element, such as lithium. In lithium fluoride, the bond is so strongly polarised that lithium's electron resides solely on fluorine, giving fluorine an octet. This type of bonding is known as ionic [ions = charged atoms or molecules], and its behaviour is comparable to the attraction between two point charges governed by Coulomb's law.

On the opposite end of the spectrum, you can have an element like fluorine bound to itself, where there is no dipole (elecronegativity difference is zero), and thus the bonding is not ionic, but covalent – a complete and equal partnership.

There are gradations of both between the extremes. Here's an important point. Similarly to how one should avoid viewing issues in black and white, chemical bonding should also be viewed with caution. There is a tendency to view bonds as either covalent OR ionic; however, it may be more useful to view them in terms of flavour or character, as bonds can have varying degrees of covalent or ionic characteristics. Thus, the middle cases contain numerous shades of both.

So what are the implications for organic chemistry? Too many to discuss in detail!  This is the fundamental phenomenon underlying much of the complexity of chemistry. However, here are some examples.

In general, the higher the boiling point/melting point, the more polarised the molecule. Considering the difference in electronegativity between oxygen (3.4) and hydrogen (2.2), water is a highly polarised molecule, as indicated by its extremely high boiling point (relative to its molecular weight) of 100 °C.

You've likely encountered this concept as the memorable slogan "like dissolves like."  The more polarised a molecule is, the greater its solubility in a polar solvent (such as water, which contains polarised O-H bonds).

Acidity – the electronegativity of the atom bound to hydrogen is an important (but not the only!) factor in determining a molecule's acidity.

For the purposes of organic chemistry, the reactivity of carbon is of the utmost importance. Atoms with a high electron density are more likely to form bonds with carbons with a low electron density, and vice versa.

As you will see when you study electrophlicity (electron-deficiency) and nucleophilicity (electron-abundance), recognising dipoles at carbon is one of the most important skills that will help you determine its reactivity.


I frequently consider electronegativity as one of the primary characteristics that give atoms their distinct personalities. You can compare electronegativity to greed, with fluorine being the most greedy and cesium being a big absent-minded idiot that constantly loses track of its lone electron.

This is a brief introduction to one of the most fundamental concepts in chemistry, but we will return to it repeatedly. Pay close attention to the differences in atomic electronegativity!

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