Chemical Bonds.doc
Michelle Melby © 2010
Chemical Bonds
Chemical bonds are forces of attraction that exist between atoms, ions, and molecules. There are many
types of chemical bonds, but we are only going to focus on ionic, covalent, and polar covalent
(hydrogen) bonds.
In 1916, the American chemist Gilbert Newton Lewis proposed that chemical bonds are formed
between atoms because electrons from the atoms interact with each other. Lewis had observed that
many elements are most stable when they contain eight electrons in their valence (outermost) shell. He
suggested that atoms with fewer than eight valence electrons bond together to share electrons and
complete their valence shells.
Ionic bonds exists between charged particles, called ions. These ions form when electrons jump from
one atom to another. Ionic bonds usually form between a metal (which loses electrons) and a nonmetal (which gains electrons). Now that the ions are oppositely charge, they are attracted to each other
by electrostatic forces. Ionic compounds form crystals and conduct electricity well. Sodium hydroxide
is used to make paper and soap; sodium chloride is table salt; and calcium carbonate can be used as an
antacid (like Tums).
Covalent bonds exist between atoms that share electrons. Covalent bonds usually form between nonmetal atoms. Covalent molecules move about freely and tend to exist as liquids or gases at room
temperature. Methane (greenhouse gas) and oxygen gas are formed through covalent bonds.
Chemical Bonds.doc
Michelle Melby © 2010
Polar covalent bonds are a type of covalent bond.
There are many types of polar covalent bonds, but we
will concentrate on one type: the hydrogen bonds of
water. In the polar covalent bonds of water, the
electrons shared by the atoms spend a greater amount
of time, on the average, closer to the Oxygen nucleus
than the Hydrogen nucleus. The result of this pattern
of unequal electron association is a charge separation
in the molecule, where one part of the molecule, the
Oxygen, has a parital negative charge and the Hydrogens have a partial positive charge. A hydrogen
bond is formed when a charged part of a molecule having polar covalent bonds forms an electrostatic
(charge, as in positive attracted to negative) interaction with a substance of opposite charge. Hydrogen
bonds are classified as weak bonds because they are easily and rapidly formed and broken under
normal biological conditions. Hydrogen bonds are extremely important in biological systems. Their
presence explains many of the properties of water. They are used to stabilize and determine the
structure of large macromolecules like proteins and nucleic acids. They are involved in the mechanism
of enzyme catalysis.
Chemical Bonds Summary: Now that you have completed the paragraphs, summarize the different
features of the three types of bonds by completing the table below:
Ionic Bond
Formed between?
How formed?
Examples of substances
containing this bond
Properties of substances
containing this bond
Covalent Bond
Hydrogen Bond
Chemical Bonds.doc
Michelle Melby © 2010
Human Bonding
Part 1: The covalent bonding of H and H to make H2 .
A good example of a covalent bond is that which occurs between two
hydrogen atoms. Atoms of hydrogen (H) have one valence electron in their
first electron shell. Since the capacity of this shell is two electrons, each
hydrogen atom will "want" to pick up a second electron. In an effort to pick
up a second electron, hydrogen atoms will react with nearby hydrogen (H)
atoms to form the compound H2. Because the hydrogen compound is a
combination of equally matched atoms, the atoms will share each other's
single electron, forming one covalent bond. In this way, both atoms share
the stability of a full valence shell.
Use this as an example with fewer students so that the whole class model in part 2 will be easier.
Students 1 and 2 represent the single protons in the nucleus of each hydrogen atom.
Students 3 and 4 represent the single electrons orbiting the nucleus of each hydrogen atom.
This can be done in the class room but will require a bit of room. The electrons should be walking or
running in orbit around their proton. Direct the electrons to form a covalent bond by running around
their hydrogen and then the other hydrogen. This will show that the two hydrogens share their
electrons to complete their valence shells and in the process become a hydrogen molecule.
Part 2: The ionic bonding of Na and Cl to make salt.
The element sodium is a silver-colored metal that reacts so violently with water that flames are
produced when sodium gets wet. The element chlorine is a greenish-colored gas that is so poisonous
that it was used as a weapon in World War I. When chemically bonded together, these two dangerous
substances form the compound sodium chloride, a compound so safe that we eat it every day - common
table salt!
+
sodium metal
chlorine gas
table salt
Assign students to represent the different parts of sodium and chlorine atoms. You can make name tags
or have the students make name tags if this helps your students remember their role.
The students representing the nucleus of each atom will be the leaders of their atom.
Student 1 represents 11 protons of Na
Student 2 represents 12 neutrons of Na
Student 3 represents 17 protons of Cl
Student 4 represents 18 neutrons of Cl
The students representing the electrons of each atom will follow the directions of the nucleus.
Students 5-15 represent the 11 electrons of Na
Students 16-32 represent the 17 electrons of Cl
Chemical Bonds.doc
Michelle Melby © 2010
Find a large open space and have the students form their atoms. The nucleus students should be in the
middle and the electrons students should be arranged into their appropriate shells. The electrons should
be running or walking around the nucleus of their atom. The nucleus of each atom will direct the
transfer of an electron to make an ionic bond and table salt!
Chemical Bonding Illustration. Short on space or time? Have the students pair up and make a cartoon
or illustration of two bonded atoms. You may use the examples in this activity or have a list of new
atoms, but they should be simple. The cartoons should be a little abstract and creative, but everything
should be labeled. This can be done on paper or white boards. (See the illustration at the beginning of
this activity.)