Performance Benchmark P.12.A.4
Students know atoms bond with one another by transferring or sharing electrons. E/S
Atoms rarely exist as independent particles in nature. Most common substances, such as
the oxygen needed to breathe, the water that makes up most of the oceans and cells, and
almost every other substance imaginable are made up of combinations of atoms held
together by chemical bonds. A chemical bond is a mutual attraction between the nuclei
and outer electrons of different atoms that binds the atoms together.
Why are most atoms bonded to each other? Most atoms that exist as independent
particles are high in potential energy when compared to atoms that are bonded. The
natural tendency favors arrangements in which potential energy is minimized. For
example, a ball placed on a hillside tends to roll down the hill, thus minimizing its
potential energy.
Atoms are composed of three major particles: protons, neutrons, and electrons. Protons
are positive particles, neutrons have no electrical charge, and electrons have a negative
charge. Protons and neutrons are relatively massive, and the electron has very little mass
when compared to protons and neutrons. The nucleus is where the protons and neutrons
are located, and the electrons are found in the electron cloud, which occupies most of the
volume of the atom.
A chemical bond is a mutual attraction between nuclei and valence electrons of adjacent
atoms that binds the atoms to each other. When atoms bond, their valence electrons are
redistributed. The way in which the redistribution occurs determines the type of bonding.
There are two main types of chemical bonding, covalent and ionic. In covalent bonding,
electrons are shared between two adjacent atoms. These shared electrons are attracted by
the nuclei of both atoms, forming a chemical bond that holds these atoms together. The
atoms being bonded have similar attractions for the electrons that they share.
Figure 1: Different representations of the covalent bonds found in methane (natural gas)
(From http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/page2.html)
In ionic bonding, electrons are transferred from one atom to another. A positive ion
(cation) is formed when electron(s) are lost, and a negative ion (anion) is formed when
electron(s) are gained. Now that there are positive and negative ions close to each other,
there is an electrostatic attraction between these oppositely charged ions, and that
attraction is the ionic bond. The atoms bonded with ionic bonds have large differences in
attraction for electrons so that the electrons are transferred.
Figure 2: Ionic bonding in sodium chloride (table salt)
(from
http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/page2.html)
To learn more about bonding between atoms, go to
http://web.jjay.cuny.edu/~acarpi/NSC/5-bonds.htm
Performance Benchmark P.12.A.4
Students know atoms bond with one another by transferring or sharing electrons. E/S
Common misconceptions associated with this benchmark:
1. Students incorrectly think that atoms want to transfer or share electrons to form
bonds.
Atoms are not alive; they do not have wants and needs. Atoms bond because it lowers
their potential energy, a tendency which is favored in nature. To learn more about this,
go to http://www.daisley.net/hellevator/misconceptions/misconceptions.pdf
2. Students incorrectly think that atoms are happy when they have an octet of
electrons.
This is similar to misconception #1 in that students attribute feelings to explain why
bonding occurs. Atoms bond because this lowers their potential energy, a natural
tendency. To learn more about it, go to
http://www.bcpl.net/~kdrews/bonding/bonding.html#Bond
3. Students incorrectly think that bonding requires the input of energy
Bonding always releases energy because atoms are in a lower potential energy position
once the bond has been formed. To learn more about this, go to
http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bond.html
Performance Benchmark P.12.A.4
Students know atoms bond with one another by transferring or sharing electrons. E/S
Sample Test Questions
1. Which particles do atoms share or transfer when they form bonds?
a. protons
b. neutrons
c. electrons
d. positrons
2. When atoms share electrons, what type of bond is formed?
a. metallic
b. covalent
c. ionic
d. hydrogen
3. When atoms transfer electrons, what type of bond is formed?
a. hydrogen
b. metallic
c. covalent
d. ionic
4. When atoms bond to each other, what type of energy change occurs?
a. energy is released
b. energy is absorbed
c. energy is stored
d. energy is unchanged
5. Why do atoms bond to one another?
a. to gain an octet of electrons
b. to become happy atoms
c. to gain kinetic energy
d. to become lower in potential energy
6. What type of attractive force is found between atoms that are bonded to one another?
a. electrostatic
b. magnetic
c. gravitational
d. nuclear
7. What happens when atoms bond to one another?
a. their nuclei join together
b. their electrons are transferred or shared
c. their nuclei undergo fission
d. their nuclei and electrons gain energy
8. In the diagram of sodium chloride above, which particles have been transferred to
form the sodium and chloride ions?
a. protons
b. electrons
c. neutrons
d. nucleons
9. Above is a diagram of methane, which has the formula CH4. Which particles are
shared between the carbon atom (dark central atom) and the hydrogen atoms (light atoms
around carbon)?
a. neutrons
b. protons
c. isotopes
d. electrons
Performance Benchmark P.12.A.4
Students know atoms bond with one another by transferring or sharing electrons. E/S
Answers to Sample Test Questions
1.
2.
3.
4.
5.
6.
7.
8.
9.
(c)
(b)
(d)
(a)
(d)
(a)
(b)
(b)
(d)
Performance Benchmark P.12.A.4
Students know atoms bond with one another by transferring or sharing electrons. E/S
Intervention Strategies and Resources
The following list of intervention strategies and resources will facilitate student
understanding of this benchmark.
1. Chemical Bonding Flash Presentations
Vision Learning has produced “Chemical Bonding”, an explanation of ionic and
covalent bonding. There are flash presentations on the reaction of sodium with
chlorine and of hydrogen atoms to each other. When compounds are formed,
their properties are different from the properties of the elements that formed them.
The direct link to “Chemical Bonding is
http://www.visionlearning.com/library/module_viewer.php?mid=55
2. Chemical Bonding Explanation
“Chemical Bonding” is a short and simple explanation of covalent and ionic
bonding. There are common examples (water and sodium chloride) of these types
of bonding as well as of hydrogen bonding. There are some links on this page
that show more detailed images of subatomic particles as well as atoms that are
bonding.
To view this page, clink on the link below.
http://www.nyu.edu/pages/mathmol/textbook/bonding.html
3. Covalent Bonds Explanation
“Covalent Bonds” is a more complex explanation of bonding and includes other
types of bonding in addition to covalent and ionic. This page also gives
schematic representations (Lewis dot diagrams) of what electrons are doing in
covalent and ionic bonding. Metallic bonding and hydrogen bonding are also
presented.
To see this website, click on http://hyperphysics.phyastr.gsu.edu/hbase/chemical/bond.html#c2
4. Covalent, Ionic, and Metallic Bonding Lessons
“ Ithaca Science Zone” has produced lessons on covalent, ionic, and metallic
bonding. Clicking on the link below will take you to covalent bonding, and there
are links on this page to describe ionic and metallic bonding. Students can access
only the pages they want to view. This is a very clear, concise site, and the
graphics give an excellent presentation of what is happening when bonds are
formed.
To access the site, go to
http://ithacasciencezone.com/chemzone/lessons/03bonding/mleebonding/covalent
_bonds.htm