Covalent bonding

Definitions & Key takeaways

A covalent bond is formed when two nonmetal atoms share valence electrons, and this electron sharing creates a strong bond between the atoms and results in the formation of a molecule. Covalent bonding is responsible for the chemical stability of most molecules and allows them to interact with one another to form larger structures.

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A covalent bond is where electrons are shared between two nonmetal atoms. Let’s start with hydrogen, which is a nonmetal on the left side of the periodic table.
Hydrogen has an atomic number equal to one which means that it has one proton and one electron. If we take two hydrogen atoms, each with its own electron, we can combine them to form a molecule, where each atom contributes one valence electron to the final molecule.
In other words, these two valence electrons are shared by both atoms in the final molecule. We can represent this process by putting two dots between the two hydrogen atoms.
These two dots represent one covalent bond. We can also represent a covalent bond by drawing a straight line between the hydrogen atoms.
One straight line means one covalent bond and represents two valence electrons. Now, in our hydrogen molecule, opposite charges attract.
So the one electron from the hydrogen atom on the left is attracted to the positively charged nucleus of the hydrogen atom on the right.
At the same time, the negatively charged electron from the hydrogen on the right is attracted to the positively charged nucleus of the hydrogen on the left.
So a mutual attractive force holds together the two atoms in a covalent bond.At the same time, like charges repel, which keeps the two positively-charged nuclei from getting any closer together.Another way to represent the hydrogen molecule is by writing H with the subscript two.
This implies that we have two hydrogen atoms in our molecule. So hydrogen is an example of a diatomic molecule, which is a molecule composed of two atoms.
There’s an easy way to remember a list of the elements that form diatomic molecules. Imagine a mad scientist who is named Dr.
Brinclhof, whose name spells out each of the diatomic molecules: “Br” is bromine, “I” is iodine, “N” is nitrogen, “Cl” is chlorine, “H” is hydrogen, “O” is oxygen, and “F” is fluorine.Let's try drawing some of the structures of these molecules, starting with the example of the fluorine molecule, F2.
Fluorine is in group 7A on the periodic table. Because the group number is equal to the number of valence electrons, we know that each fluorine atom has seven valence electrons around it.
Fluorine is most stable when it has a full set of eight electrons around it, which is referred to as an “octet.” For this reason, it will tend to form bonds that allow it to get an octet of electrons.
It gains an electron by sharing one of the seven electrons from another fluorine atom to create a covalent bond. There are therefore two shared electrons in the covalent bond, one from each atom.
Each fluorine atom in a diatomic fluorine molecule has a full octet, consisting of seven electrons from its original set of electrons, and the eighth electron shared with the other, neighboring fluorine atom.Now, let’s look at the oxygen molecule, O2.
Oxygen is in group 6A on the periodic table, so each oxygen atom has six valence electrons. We can draw these in around each oxygen atom.
We can see that we still don’t have an octet around each oxygen atom, because each oxygen atom is missing two electrons from its octet.
So to get an octet of electrons, the atoms need to share four electrons with one another, and that happens by having a double bond between the two oxygen atoms.
We indicate a double bond with a double line in drawings of the molecule.Now, let's look at the nitrogen molecule, N2. Nitrogen is in group 5A on the periodic table, so each nitrogen has five valence electrons.
We can draw these in around each nitrogen atom. We can see that we still don’t have an octet around each nitrogen atom, because each nitrogen atom is missing three electrons from its octet.
As a result, two nitrogen atoms will share six electrons with each other, resulting in a triple bond between the nitrogen atoms and an octet around each nitrogen.
We indicate a triple bond with a triple line in drawings of the molecule.Molecules don't have to be diatomic. For example, we can draw out the dot structure for methane, which has the chemical formula CH4.
Carbon is in group 4A on the periodic table, so carbon has four valence electrons. We can draw these in around the carbon atom.
Next, recall that hydrogen is in group 1A. So each hydrogen has one valence electron.
Notice how the four hydrogens all fit around the central carbon to form four carbon-hydrogen bonds. Carbon is now surrounded by eight electrons, resulting in an octet, and thus our final, stable molecule.
Now, notice that hydrogen does not follow the octet rule. That’s because the first period has a shell that holds a maximum of two electrons.
Since Hydrogen is in the first period, it is stable with only two electrons around it. Finally, we can look at water, which has the molecular formula H2O, which means that it has two hydrogen atoms and one oxygen atom.
We already know hydrogen is in group 1A, and oxygen is in group 6A on the periodic table, so each oxygen has six valence electrons.
We can draw these in around the oxygen atom. As before, each hydrogen has one valence electron.
If we draw the water molecule out, then we can see how each hydrogen shares its electron with oxygen. The final dot structure shows that oxygen has an octet of electrons around it and each hydrogen has two.
##SummaryAlright, as a quick recap... covalent bonds form when non-metal atoms share their valence electrons among themselves, in order to allow all of the atoms to have a full octet.
Hydrogen is one of the exceptions to the octet rule because it ends up with only two electrons around it. Many elements such as oxygen, nitrogen, and hydrogen form diatomic molecules.
In a water molecule, an oxygen atom gains an octet of electrons by sharing electrons with two hydrogen atoms. gains an octet of electrons by sharing electrons with two