Covalent Bonds
Sharing Electrons Between Non-Metal Elements
The simplest compounds which form Covalent Bonds are those
that result from a sharing of electrons between Non-Metal Elements
(Groups IIIA through VIA of the Periodic Table and Hydrogen (Group
IA).
The Non-Metal Elements such as Carbon, Nitrogen and Oxygen in Groups
IVA, VA and VIA, have 4, 5 and 6 electrons in their outermost shell. The
driving force for the reactivity of all elements which leads to the
formation of chemical compounds is the need to reach the low energy
state of a full outermost shell.
As we discussed in our Ionic Bonds section, the Metal
Elements and the Halogens need to loose or gain only one or two
electrons to have this stable low-energy full outermost shell.
Unlike Metal Elements, the Non-Metal Elements Carbon, Nitrogen and
Oxygen typically prefer to share electrons with other Non-Metal Elements
or with Hydrogen in order to attain the stable full outermost shell.
To understand the fundamental properties of Non-Metals and Hydrogen that
lead to Covalent Bonds we refer you to our section on Atomic
Structure.
Covalent Bonds of Carbon and Hydrogen - Hydrocarbons
The best way to understand Covalent Bonds is to illustrate how some
common compounds are formed when the most common Non-Metal Elements,
Carbon, Nitrogen and Oxygen share electrons with each other and with
Hydrogen. We begin with the compounds formed from Carbon and Hydrogen
commonly called Hydrocarbons.
As we learned in our section on Atomic Structure elements can be
represented by concentric circles representing the shells containing
electrons in their orbitals as shown in the picture above.
There is another much more convenient "short hand" representation of the
atomic structure of an element called the Lewis Atomic Structure. In
this representation only the "reactive electrons", sometimes called the
"valence electrons", in the Outer Shell are shown. The Lewis Structure
of the element Carbon (C) is shown in the picture above.
Carbon has four electron in its Outer Shell. Since, Carbon is a Non-
Metal it does not readily loose its outer shell electrons to become an
ion. As you can see from the Lewis Structure of Carbon, it stands ready
to share four electrons with four Hydrogen atoms.
The next step in understanding the bonding between Carbon and Hydrogen in Hydrocarbons is to show the Lewis Atomic Structure of Hydrogen
(H), which has only one electron. The full shell diagram of Hydrogen is
shown in the picture above along with the Lewis Atomic Structure.
Now that we have constructed the Lewis Structures of Carbon and
Hydrogen we are ready to understand the bonds that make up Hydrocarbons.
Methane - In the above picture we show how one Carbon atom shares
electrons with four Hydrogen atoms to form the four Covalent Bonds of
the most common Hydrocarbon, Methane. Methane is the main component of
natural gas.
We have given the electrons of Carbon and Hydrogen different shapes and
colors so that you can see how the electrons are shared.
Ethane - When two Carbon atoms share electrons with each other
and six Hydrogen atoms, we form the seven covalent bonds of another
common Hydrocarbon, Ethane.
You can see from the color-coded and different shaped electrons
that each Carbon atom shares one electron with another Carbon atom and
one electron with each of three Hydrogen Atoms.
Propane - When three Carbon atoms share electrons with each other
and eight Hydrogen atoms we form the 10 Covalent Bonds of another common
Hydrocarbon, Propane.
You can see from the color-coded and different shaped electrons that the
first and last Carbon atoms share one electron with another Carbon atom
and one electron with each of three Hydrogen Atoms. The middle Carbon
atom shares one electron with two other Carbon atoms and one electron
with each of two Hydrogen atoms.
Covalent Bonds of Nitrogen and Hydrogen - Ammonia
We continue our explanation of the bonding between Non-Metals with another simple
compound - Ammonia, the main component of many household cleaners. As
before, we start with the atomic structures of Nitrogen (see picture
below) and Hydrogen (see previous picture).
The full shell atomic structure of Nitrogen showing all the shells
and electrons, along with the Lewis Structure of Nitrogen, which shows only
the five "reactive electrons" in the Outer Shell is shown in the above
picture.
Now that we have constructed the Lewis Structures of Nitrogen and
Hydrogen we are ready to understand the bonding of the Ammonium
molecule.
Ammonia - In the above picture we show how one Nitrogen atom
shares one electron with each of three Hydrogen atoms to form the three
bonds of the common household cleaner, Ammonia.
We have given the electrons of Nitrogen and Hydrogen different shapes and
colors so that you can see how the electrons are shared.
You can see from the color-coded and different shaped electrons that the
Nitrogen atom shares one electron with three Hydrogen Atoms to form the
three bonds of Ammonia.
Covalent Bonds of Oxygen and Hydrogen - Water
The full shell atomic structure of Oxygen showing all the shells
and electrons, along with the Lewis Structure of Oxygen, which shows only
the six "reactive electrons" in the Outer Shell is shown in the above
picture.
Now that we have constructed the Lewis Structures of Oxygen (see
above picture) and Hydrogen (see previous picture) we are ready to
understand how the bonds of the Water molecule are formed.
Water - In the above picture we show how one Oxygen atom shares
electrons with each of two Hydrogen atoms to form the two Covalent Bonds of
one of the most abundant compounds on Earth, Water.
We have given the electrons of Oxygen and Hydrogen different shapes and
colors so that you can see how the electrons are shared.
You can see from the color-coded and different shaped electrons that the
Oxygen atom shares one electron with each of two Hydrogen Atoms.
From the above discussion it should be clear that the secret to
understanding Covalent Bonds is to understand the atomic structure of the
participating elements.
This same process of starting with the full shell atomic structure
representation of each element involved in a Covalent Bonded molecule and then
proceeding to the Lewis Structures of the elements and creating a sharing of electrons
to give each element a full outer shell can be used for any Covalent compound.
Click here for a tutorial on the Periodic Table
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