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Covalent bonding occurs between the atoms of non-metals . The outermost orbitals of the atoms overlap so that unpaired electrons in each of the bonding atoms can be shared. By overlapping orbitals, the outer energy shells of all the bonding atoms are filled. The shared electrons move in the orbitals around both atoms. As they move, there is an attraction between these negatively charged electrons and the positively charged nuclei, and this force holds the atoms together in a covalent bond.
Covalent bonding is a form of chemical bonding where pairs of electrons are shared between atoms.
Below are a few examples. Remember that it is only the valence electrons that are involved in bonding, and so when diagrams are drawn to show what is happening during bonding, it is only these electrons that are shown. Circles and crosses represent electrons in different atoms.
The following simulation allows you to build some simple covalent molecules.
How do hydrogen and chlorine atoms bond covalently in a molecule of hydrogen chloride?
A chlorine atom has 17 electrons, and an electron configuration of 1s 2s 2p 3s 3p . A hydrogen atom has only 1 electron, and an electron configuration of 1s .
Chlorine has 7 valence electrons. One of these electrons is unpaired. Hydrogen has 1 valence electron and it is unpaired.
The hydrogen atom needs one more electron to complete its valence shell. The chlorine atom also needs one more electron to complete its shell. Therefore one pair of electrons must be shared between the two atoms. In other words, one electron from the chlorine atom will spend some of its time orbiting the hydrogen atom so that hydrogen's valence shell is full. The hydrogen electron will spend some of its time orbiting the chlorine atom so that chlorine's valence shell is also full. A molecule of hydrogen chloride is formed ( [link] ). Notice the shared electron pair in the overlapping orbitals.
How do nitrogen and hydrogen atoms bond to form a molecule of ammonia (NH )?
A nitrogen atom has 7 electrons, and an electron configuration of 1s 2s 2p . A hydrogen atom has only 1 electron, and an electron configuration of 1s .
Nitrogen has 5 valence electrons meaning that 3 electrons are unpaired. Hydrogen has 1 valence electron and it is unpaired.
Each hydrogen atom needs one more electron to complete its valence energy shell. The nitrogen atom needs three more electrons to complete its valence energy shell. Therefore three pairs of electrons must be shared between the four atoms involved. The nitrogen atom will share three of its electrons so that each of the hydrogen atoms now have a complete valence shell. Each of the hydrogen atoms will share its electron with the nitrogen atom to complete its valence shell ( [link] ).
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