Types of Chemical Bonds

The Two Major Types of Bonds

Covalent Bond: This type of bond typically occurs between two non-metals, and it is the result of electron sharing.

Ionic Bond: This type of bond typically occurs between a metal and a non-metal, and it is the result of electron transfer.

We will first look at covalent bonds. The covalent bond results from two atoms each providing one electron to form a bond.

This means that each atom effectively has one extra electron. This may be a bit confusing, as you might not understand how an atom can share an electron to another atom without losing it. The following gallery shows just what is happening between the two atoms. It is important to note that each covalent bond involves two electrons: one from each atom. This means that if you have two pairs of electrons involved, we would be looking at a double bond.

Another important aspect of atomic bonds is the degree to which an atom attract electrons: electronegativity. This determines how strongly an atom holds onto an electron in a bond. In the first example in the gallery, the H2 bond, the two Hydrogen atoms have the same electronegativities. This means that they both hold onto the electrons equally. Typically, the non-metals don’t have extremely different negativities, but you will sometimes see a fair difference. The second example, water (H2O) shows this.

When Oxygen forms a covalent bond with hydrogen, it forms what is known as a polar covalent bond. This means that the electrons are not evenly shared between the two atoms. Instead, the electrons tend to gather more commonly around the more electronegative atom, in this case oxygen. Due to the uneven distribution of electrons, we see the formation of a dipole. This means that the molecule formed will have a partial charge on either side. The gallery illustrates this, giving color to the charge, red for negative and blue for positive. You can think of a dipole as a magnet, which has two sides to it. The more electronegative side will tend to have more electrons, making it have a partially negative charge. As the molecule as a whole is uncharged, this means that a partially positive charge results on the other side of the molecule.

Therefore, ionic bonds typically occurs between metals and non-metals because metals tend to have much lower electronegativities than nonmetals.

Metallic Bonds:

We have covered bonds between two nonmetals, a metal and a nonmetal, but what about two metals? You may think that two metals would have a covalent bond form, as they would have low differences in electronegativities. This isn’t quite true, however, as the electronegativities of each atom is low. This means that while the atoms are sharing their electrons, they don’t necessarily congregate between the two atoms, like a typical covalent bond.

A metal is an extended structure. Its valence electrons are delocalized across many metal centers, while the positive ion cores form the lattice. This model helps explain why metals conduct electricity and can be reshaped without simply breaking into isolated molecules. It differs from a covalent molecule and from an ionic lattice of positive and negative ions.

Let’s move onto a quick review of characterizing atomic bonds. In the following review widget you will be tested on your understanding of the different bonds.

Valence Electrons:

Electron-density drawings show where electrons are likely to be found in a bonding model. They do not show tiny electrons following circular paths. When a bond forms, attraction involving the nuclei and electron density competes with nucleus–nucleus and electron–electron repulsion. A useful diagram makes the shared or delocalized density visible without turning it into a planetary orbit.

When an atomic bond forms, it involves only these valence electrons, meaning that the number of bonds an atom can make is determined by the number of valence electrons an atom has. This is why hydrogen can only form one bond, but oxygen can bond with two atoms. More on that in the following section.