Chemical Bonding Patterns: The Basics

Few elements on the periodic table are satisfied with their electron arrangement. This is due to an imbalance felt between the positive and negative forces of attraction at play within the atom. Bonding can then be viewed as a form of correction the atoms undergo that result in the most stable electron configuration possible, a filled shell. This pattern is known as The Octet Rule. It is named so because second row elements and below need eight electrons to fill their valence shells. This is a rule of thumb, and there are many exceptions to it, but generally elements will combine in a way that results in there being 8 electrons in their valence shells. One important exception is in the closest electron orbital to the nucleus, this orbital only requires two electrons to fill it.

The electrons needed to do this aren't free, they have to come from somewhere. This is where atomic bonding comes in. This occurs when two atoms, dissatisfied with their electron configurations come together to share/exchange electrons to achieve a more stable configuration. There are two major types of atomic bonding:

Covalent Bond- a bond in which electrons are shared.

Ionic Bond- a bond which occurs after electrons are transferred.

When you think covalent, always, always think sharing. The atoms come together and share electrons between each other, in a sort of meshing pattern. This is the most common type of bond seen, and occurs exclusively in non-metals.

Ionic bonds, on the other hand, occur when the attraction of one atom is enough to tear an electron from another atom's valence shell and make it part of its own. The receiving, or stealing, atom has a more positive charge than the atom it's taking from, which makes the negatively-charged electron more attracted to it than the atom it was a part of before.

This exchange causes an ionization, the changing of an atoms charge from its neutral state, in both atoms. The exchange results in a more stable configuration for the second atom, but what about the atom the electron was taken from in the first place? It then seeks to deionize and restabalize. An ionic bond forms when the positively-charged (electron-deficient) atom is subsequently attracted to the more negatively charged (electron-rich) atom. This attraction occurs immediately following the electron transfer. In this way, the term "ionic bond" is a bit of a misnomer. A more appropriate term would be "ionic attraction"

A "real life" parallel to ionic vs. covalent bonds is in the dynamic of a couple holding hands vs. a person being robbed, respectively. The covalent couple share a mutual attraction and are more stable together than alone, and there is a shared bond between them. A person being robbed and in close pursuit of the robber (atom) and stolen item (electron) more closely parallels the dynamic of ionic bonding, as there is no shared link between the atoms, just an attraction.

You may be asking, how does ionic bonding favor a more stable configuration for both atoms when one of them clearly gets the shaft? For this, you have to consider that different elements are more attractive than others to electrons, this is called their electronegativity, and it generally increases as the atom approaches a more stable configuration. If an atom with a weak electronegativity (such as sodium, which has an "extra" electron) passes by an element that has a high electronegativity (such as fluorine, which needs one more electron to satisfy the octet), the fluorine will rob the sodium of its electron to gain a more stable configuration. The sodium is now mildly unhappy, due to a now larger positive force from its nucleus than a negative force from its electrons. It will then have an equally mild attraction to the electron that was lost. This creates a situation that is lower in energy and more stable overall.

The molecule formed by this bond in particular is called sodium fluoride, and it is a prime example of a salt. A salt is any compound formed by ionic bonds. Given the nature of their bonds, salts are very weak and typically very soluble. Acids and bases are typically found as salts (HCl and NaOH) because the hydrogen (H) and hydronium (OH-) easily dissociate from chlorine and sodium, respectively, in a solution of water. All salts are named in this way; metal first, non-metal second and affixed with the suffix, "ide".