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Transcript
Atoms:
The Building Blocks of Matter
from the six-part
Elements of Chemistry Series
Produced by
Algonquin Educational Productions
Distributed by...
800.323.9084 | FAX 847.328.6706 | www.unitedlearning.com
This video is the exclusive property of the copyright holder. Copying, transmitting, or reproducing in any form, or
by any means, without prior written permission from the
copyright holder is prohibited (Title 17, U.S. Code Sections
501 and 506).
© 2003 Algonquin Educational Productions
Table of Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Links to Curriculum Standards . . . . . . . . . . . . .1
Student Objectives . . . . . . . . . . . . . . . . . . . . . .1
Summary of the Program . . . . . . . . . . . . . . . . .2
Pre-Test and Post-Test . . . . . . . . . . . . . . . . . . .4
Teacher Preparation . . . . . . . . . . . . . . . . . . . . .4
Student Preparation . . . . . . . . . . . . . . . . . . . . . .5
Description of Blackline Masters . . . . . . . . . . .6
Answer Key . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Discussion Questions . . . . . . . . . . . . . . . . . . . .10
Follow-Up Activities . . . . . . . . . . . . . . . . . . . .11
References . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Script of Narration . . . . . . . . . . . . . . . . . . . . . .13
This video is closed captioned.
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with this program, Atoms: The Building Blocks of Matter. This right is
restricted only for use with this program. Any reproduction or duplication
in whole or in part of this guide and the blackline master handouts for any
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Atoms: The Building Blocks of Matter
from the six-part Elements of Chemistry Series
Grades 9 to 12
Viewing Time: 20 minutes
INTRODUCTION
Atoms: The Building Blocks of Matter is part of the Elements
of Chemistry Series, a six-part series of programs to help students understand the fundamental concepts of chemistry. The
attractive images and engaging narration of the program have
been designed by educators and filmmakers to help students
understand the sometimes complicated and obscure explanations of this important branch of science.
In the late nineteenth and early twentieth centuries, a number of
remarkable theoretical and experimental developments led
chemists to a new understanding of the atom, the fundamental
building block of all matter. This program describes the important ideas that have been developed in chemistry and gives students a clear understanding of the structure of atoms and how
they function. The program provides a comprehensive introduction to this fascinating area of science appropriate for high
school students.
LINKS TO CURRICULUM STANDARDS
The Elements of Chemistry Series, is based on the "National
Science Educational Standards" for "Physical Science," grades
9-12, (Content Standard B).
STUDENT OBJECTIVES
After viewing the program and participating in the various follow-up activities, students should be able to:
• Describe the basic structure of the atom and be able to name
and locate protons, neutrons, and electrons.
1
• Explain how the positive electrical charge of the proton and
the negative electrical charge of the electron hold the atom
together.
• Define and describe an isotope.
• Describe the fundamental difference between elements.
• Explain how the atomic number of an element is determined.
• Define atomic mass and atomic mass unit (amu).
• Define and describe an ion.
• Explain the method chemists use to write the precise description of ions.
• Describe radioactive decay or radiation.
• Give a general explanation of Max Planck's Theory that the
energy of electrons can only absorb or emit energy in units or
chunks called quanta.
• Describe the Uncertainty Principle.
• Explain why chemists use the term atomic orbitals to describe
the motion of electrons.
• Identify quantum numbers and why they are important.
SUMMARY OF THE PROGRAM
Chemistry deals with one of the most basic questions that have
puzzled us since the beginning of time: What is the physical
makeup of the world? The answer of chemistry is that atoms
are the fundamental building blocks of all matter.
2
It was not until the early part of the twentieth century that
research demonstrated that atoms actually existed and it took
another thirty years before a comprehensive theory was developed to explain how they functioned. We now know that the
nucleus of an atom is composed of positively charged protons
and neutrons that carry no charge. Spinning about the nucleus
are electrons that have a negative charge. Positive and negative
electrical charges attract each other and it is that attraction that
holds the atom together.
There are different types of atoms with different numbers of
protons, neutrons, and electrons. They are called elements. An
electrically neutral atom has the same number of protons and
electrons. Usually an atom has the same number of protons and
neutrons but when it has more or less neutrons than protons, it
is called an isotope.
There are 92 elements found naturally in the universe and another twenty or more that have been created in laboratories. An
element gets its atomic number by the number of protons in its
nucleus. The periodic table is an arrangement of elements by
their atomic number and other characteristics.
An electrically neutral atom has an equal number of protons
and electrons, but electrons have the ability to move from atom
to atom. When an atom has more or less electrons than protons,
it is called an ion. When it has more electrons than protons it is
a negatively charged ion and when it has more protons than
electrons, the ion has a positive charge.
Quantum Theory was developed to explain the behavior of
atoms. This theory holds that electrons circle the nucleus of
atoms with a certain unit or quanta of energy. The Uncertainty
Principle says that it is impossible to know both the position
and velocity of electrons at the same time, but electrons with a
given energy follow certain patterns called atomic orbitals. The
four quantum numbers describe the behavior of electrons.
3
Electron behavior is of key importance in understanding how
elements combine into compounds and it is the various compounds that make up the millions of substances in the universe.
PRE-TEST and POST-TEST
Blackline Master #1, Pre-Test, is an assessment tool intended
to gauge student comprehension prior to viewing the program.
Remind your students that these are key concepts upon which
they should focus while watching the program.
Blackline Master #7, Post-Test, can be compared to the results
of the Pre-Test to determine the changes in student comprehension after viewing the program and participation in the activities.
TEACHER PREPARATION
Before presenting this program to your students, we suggest
that you preview the program and review this guide and accompanying Blackline Master activities in order to familiarize yourself with the content. Feel free to duplicate any of the Blackline
Masters and distribute them to your students.
As you review the materials presented in this guide, you may
find it necessary to make some changes, additions, or deletions
to meet the specific needs of your class. We encourage you to
do this. Only by tailoring this program to your class will your
students obtain the maximum instructional benefits afforded by
the materials.
We suggest that you first show the program in its entirety to
your students. This is an introduction to the complex subject of
modern chemistry, and at this stage it is helpful that students
gain an overview of the concepts and material in the program.
A number of lesson activities will grow out of the content of the
program and, therefore, the presentation should be a common
experience for all students.
4
After the introduction, the program is divided into chapters with
the following titles:
• The Structure of Atoms
• Elements and Isotopes
• Ions
• Nuclear Stability
• Quantum Theory
• Electron Behavior
These chapters vary in length from three to five minutes. After
the students have seen the entire program, lessons could be
designed around these different chapters. A chapter could be
shown at the beginning of the class, and the balance of the class
time, and subsequent classes, could be spent examining the subject matter in the program in greater depth.
STUDENT PREPARATION
It is important that students work through the material and
familiarize themselves with the vocabulary, concepts, and theories that scientists use to understand this field.
If the students have a textbook that they are following, assign
the relevant reading before the lesson. As students work
through the material, they will encounter a number of unfamiliar words and concepts. Most of these words are highlighted in
the program. An additional list of words is provided in Blackline Masters #2a-c, Vocabulary Definitions and Activities.
The program concludes with a ten-question Video Quiz that
may be used to gauge students' comprehension immediately
after the presentation of the program. Blackline Master #6,
Video Quiz, is a printed copy of the questions, which may be
reproduced and distributed to the students. The answers to the
questions appear in the answer key of this Teacher's Guide.
5
DESCRIPTION OF BLACKLINE MASTERS
Blackline Master #1, Pre-Test, should be given to students
before viewing the program. When these answers are compared
to the quiz results, it will help you gauge student progress.
Blackline Master #2a, Vocabulary Definitions, will introduce
students to unfamiliar words and concepts used in this program.
Blackline Master #2b, Use the Right Word, and Blackline
Master #2c, Word Match, are activities designed to help reinforce key concepts and vocabulary.
Blackline Master #3, Connected and Not Connected, will
help students identify their knowledge of key vocabulary terms
and the context in which they are used.
Blackline Master #4, Crossword Puzzle, reinforces key concepts and vocabulary.
Blackline Master #5, Creative Writing Story Ideas, will
allow students to think creatively while incorporating scientific
principles and vocabulary covered in this program.
Blackline Master #6, Video Quiz, is a printed version of the
Video Quiz that appears at the end of the program.
Blackline Master #7, Post-Test, may be used to evaluate student progress after completing this lesson.
ANSWER KEY
Blackline Master #1, Pre-Test
1. True
6. True
2. False
7. True
3. False
8. False
4. True
9. False
5. False
10. True
6
Blackline Master #2b, Use the Right Word
1. orbital
2. ion
3. Isotopes
4. proton
5. neutron
6. radiation
7. quantum
8. Uncertainty
9. transuranium
10. element
Blackline Master #2c, Word Match
electronnegatively charged particle
element-
atom with a unique number of protons
ion-
atom with more or less electrons than protons
isotope-
atom with more or less neutrons than protons
nucleus-
center of the atom
orbitals-
the shapes of the orbits of the electrons
proton-
positively charged particle
quarks-
sub-atomic particles
radioactive-
when a nucleus of an element decays
transuranium- elements with atomic numbers greater than 92
7
Blackline Master #3, Connected/Not Connected
1. Protons
neutrons
2. Atomic number atomic mass
3. electron
electrical
4. Ions
isotopes
5. periodic
elements
6. Fission
fusion
7. Gamma
alpha
8. Hydrogen
oxygen
9. Quantum
energy
10. Uncertainty
predictability
Blackline Master #4, Crossword Puzzle
1
2
3
R A D
I
A
T
I
O N
T
C
4
O
5
8
M
6
N
M
7
M A
T
T
S
N
L
E C T
U
U
S
T
R
14
I
O R B
11
L
E
L
E M E N T
L
S
T
9
C
12
E
E R
A M U
S
U
10
I
I
R O N
N
T
13
P
Y
R
T
O
15
A
O
S O T O P E
N
T
Q U A N T
U M
Blackline Master #6, Video Quiz
1. True
6. True
2. False
7. ion
3. elements
8. True
4. False
9. orbitals
5. isotopes
10. False
8
Blackline Master #7, Post-Test
1. electrical
2. element
3. Transuranium
4. Uncertainty
5. False. The Uncertainty Principle holds that it is impossible to
know the location and velocity of electrons at the same time.
6. False. Electrons circle the nucleus of atoms in complicated
patterns called orbitals. The shape of the orbitals is dependent
on the energy level of the electrons.
7. True
8. False. Ions can have more or fewer electrons than protons.
9. False. Every element has a different atomic mass because
they have varying numbers of protons, neutrons and electrons.
10. The greatest difficulty that scientists faced in their study of
atoms was their incredibly tiny size, but there were other difficulties. The behavior of electrons does not follow predictable
patterns, the orbital shapes are complicated, and one of the most
difficult problems was that electrons are both matter and energy. Despite these and other problems, Quantum Theory was
developed that provides an accurate description of atoms and
sub-atomic behavior.
11. The atomic mass unit, or amu, is a measurement of the mass
of elements. A neutral carbon atom was given the amu of 12
and this became the unit of measurement that was used to determine the mass of all elements. The amu of an element is very
important because it helps in understanding how elements react
when combined with other elements.
12. The Uncertainty Principle holds that it is impossible to give
the precise location and velocity of an electron at the same time.
Because of this uncertainty, all that can be done is to describe
the likelihood or probability of an electron's location. The
cloudlike image of orbitals, used by chemists, suggests the
probable location of the electron. The area of the orbital where
the cloud appears denser suggests that there is more likelihood
of the electron being in that area than when the cloud appears
less dense.
9
DISCUSSION QUESTIONS
1. Why is chemistry considered one of the basic sciences?
Chemistry addresses the question, “What is the make up of matter?” Knowledge of the makeup of matter is essential not only
in chemistry but in a whole host of different sciences such as
physics, biology, earth sciences, and every branch of the health
sciences from medicine and nursing to pharmacy and dentistry.
Chemistry is often used to gather evidence in police work and
has become a vital tool in dating artifacts and tissue in archeology. Because chemistry underlies an understanding of these
and other sciences it has come to be called one of the "basic
sciences.” Students contemplating careers in a wide number of
fields must have a sound understanding of the science of chemistry.
2. Are the electrical charges that exist between the proton and
electron in atoms the same as the electricity that illuminates a
light bulb?
Yes. There are four forces in the universe: gravity, electromagnetism, and the strong and weak nuclear forces in atoms.
Electromagnetism is found in light from the sun and stars, static electricity, such as lightening and electricity that powers
light bulbs, household appliances, and various kinds of machinery. The force in all of these forms of electricity is electromagnetism.
3. Why do chemists focus all of their attention on atoms and not
smaller particles like quarks, leptons, and bosons?
In fact, a great deal of research is being carried out by physicists on sub-atomic particles but it has little impact on chemistry. The chemical behavior of matter can be explained almost
entirely by understanding the behavior of protons, neutrons,
and electrons. When elements combine into covalent or ionic
bonds, they result in the millions of substances that we find in
the natural world. It is atoms that are the fundamental building blocks of all matter.
10
4. Louis de Broglie proposed the idea that electrons were both
particles of matter and a form of energy. How can that be possible?
Physicists point out that there are only two fundamental things
in the universe: matter and energy. In our world matter and
energy are always separate, but in the sub-atomic world, things
are different. Electrons are particles of matter as well as a form
of energy. They move in waves like a form of energy. Photons,
the energy of light, are also particles. Like electrons, photons
are both matter and energy and they move in waves.
5. Why is the "Uncertainty Principle" so controversial in science?
One of the founding principles of classical science is that if all
of the factors can be known, the physical behavior of physical
objects can be predicted exactly. The Uncertainty Principle
holds that we can never know the location and velocity of an
electron at the same time. It contradicts classical science. Even
Einstein had problems with this theory. "God does not play dice
with the universe," he commented. Despite this, the Uncertainty
Principle is now an established principle of science.
FOLLOW-UP ACTIVITIES
The following activities and projects might prove useful to students studying atoms and chemistry.
1. Draw diagrams showing the structure of the following three
types of elements: hydrogen (H), oxygen (O), and iron (Fe).
2. Why is the atomic mass of an element important? Explain
the difference between atomic mass and the atomic mass unit
(amu).
3. Research and give a scientific explanation of the use of carbon 14 to date objects that were once alive. Write a report on
your findings.
11
4. Explain why ionic solutions are good conductors of electricity. Draw a diagram illustrating your explanation.
5. When atomic or hydrogen bombs are exploded, they release
radiation into the atmosphere. Why is this a serious health problem? In your opinion, does this change the nature of war in the
modern era? Write a report discussing the ethics of modern
warfare.
6. Write a brief history of the development of Quantum Theory
and the major scientists who contributed to its development.
This theory has been called one of the most important scientific developments of the modern era. Explain why you agree or
disagree with this statement.
7. Research the Uncertainty Principle and write a report
explaining why it is considered a radical departure from classical science. In your opinion, does this theory force us to conclude that we must give up on the scientific assumption that the
movement of all physical things can be predicted?
8. Draw diagrams of each of the electron orbital shapes.
9. Draw a chart showing how electrons fill the orbitals of the
first 18 elements in the periodic table.
10. Research the difference between alchemy and chemistry.
Why is alchemy not considered a science?
REFERENCES
There are many excellent books and websites dealing with
atoms and matter that are appropriate for students. The following is a short list.
Books:
LeMay, Eugene, Karen M. Robblie, Herbert Beall, Douglas
Brower, Chemistry: Connections to Our Changing World,
Englewood Cliffs, New Jersey: Prentice Hall, 1996.
12
McMurry, John, Robert C. Fay, Chemistry, Englewood Cliffs,
New Jersey, Prentice Hall: 1995
Smoot, Robert C., Richard G. Smith, Jack Price, Chemistry,
Glencoe: McGraw Hill, 1998
Internet Sites:
www.howstuffworks.com/atom.htm
http://highschoolhub.org/hub/chemistry.cfm
www.dist214.k12il.us/users/asanders/atom.html
http://education.jlab.org/atomtour/
www.chemistry.mcmaster.ca/faculty/dader/aim
http://dir.yagoo.com/Science/Chemistry/
www.dist214.k12il.us/users/asanders/chemhome2.html
SCRIPT OF NARRATION
The study of chemistry touches on almost every aspect of our
environment and human life. It helps us understand why icebergs float, how to get the fizz in soda pop, and what gives lipstick its red color. Knowledge of chemistry is essential in biology, medicine, ecology, and even archeology. It provides answers to one of the most basic questions that have puzzled us
from the beginning of time: What makes up all the things in the
world? This program will focus on atoms, the tiny units that are
the fundamental building blocks of matter.
THE STRUCTURE OF ATOMS
The roots of the modern atomic theory can be traced back to
Democritus, one of the ancient Greeks, but it was only a little
over 100 years ago that the evidence was found to prove that
atoms actually existed. In 1897, J.J. Thomson, a British physicist, found a tiny negatively charged particle that he called an
13
electron. A few years later, Ernest Rutherford found evidence
of the nucleus of atoms. With such painstaking research, a picture of atoms began to emerge.
We now know that atoms are composed of protons, neutrons,
and electrons. The nucleus comprises protons and neutrons.
Each proton carries one fundamental unit of positive electrical
charge. Neutrons have no charge. The electrons move about in
the space around the nucleus. They carry a negative electrical
charge. Positive and negative electrical charges attract each
other and it is that attraction that holds the atom together.
The reason why it was so difficult to understand atoms is that
they are so incredibly tiny. To give an idea of their size, about
50 million atoms of solid material lined up in a row would
measure one centimeter, about the thickness of a single french
fry. Atoms are tiny but the different parts of an atom are even
a fraction of that size. Compare the nucleus of an atom to the
size of a marble at the starting line of a 100-meter track. The
electron would be the size of a speck of sand half way down the
track. The rest of the atom is empty space.
Although atoms are considered the smallest units of matter,
research has shown that there are more than one hundred subatomic particles, but for the purposes of chemistry, they have no
immediate impact. Chemical behavior of matter can be understood simply in terms of protons, neutrons, and electrons.
ELEMENTS AND ISOTOPES
We have described the basic structure of atoms but there are different types of atoms with different numbers of protons, electrons, and neutrons. They are called elements. The simplest
element is hydrogen. It has one proton and one electron.
Hydrogen is by far the most common element in the universe.
Other elements have varying numbers of protons and neutrons.
This oxygen atom has eight protons and usually, eight neutrons.
When it is electrically neutral, an oxygen atom also has eight
electrons. In total, there are 92 elements found naturally in the
14
universe and another twenty or more that have been created in
laboratories. This periodic table is a list of all the elements.
Every element has an atomic number, which is the number of
protons that are found in the nucleus of the atom. Hydrogen has
the atomic number of 1, and only has one proton. Iron's atomic number is 26; it has 26 protons. Gold is 79 and uranium has
the atomic number 92. For any element, the number of neutrons
in the nucleus can vary from atom to atom. Atoms of an element with different numbers of neutrons are called isotopes of
the element. For example, most carbon atoms have 6 protons
and 6 neutrons, but carbon atoms frequently have 7 neutrons.
This is called carbon 13. Carbon can also have 8 neutrons, carbon 14. The number of the isotope is determined by adding the
number of protons and neutrons.
The atomic mass of an atom is the total mass of all its protons,
electrons, and neutrons. Scientists use the term mass, rather
than weight, because it is a measure of the total quantity of an
object's matter. In space, all objects are weightless but they
never lose their mass.
Every element has a different atomic mass. The unit of measurement is defined as the atomic mass unit, or amu. Chemists
base the unit of measurement on the mass of the element carbon. A carbon atom was defined as having an atomic mass of
12 amus. Thus, one amu is 1/12th of the mass of a carbon 12
atom and is roughly equal to the mass of a proton or a neutron.
But if you look at the periodic table carbon does not have an
atomic mass of 12. Any natural sample of an element contains
certain percentages of isotopes, which have different mass values. On the periodic table, the value given for atomic mass is
an average mass of the element including all isotopes. So the
averaged atomic mass of carbon is 12.011. The atomic mass for
all of the elements is determined in this way.
The atomic mass of the different elements varies considerably.
Hydrogen, with only one proton and one electron, is the lightest element with an average mass of 1.00794. As a general rule,
15
the higher the atomic number of the element, the greater its
mass. Isotopes of an element have a different mass but essentially the same chemical properties.
IONS
A neutral atom has an equal number of protons and electrons,
giving it a neutral electrical charge. The positive electrical
charges of the protons are balanced by the negative electrical
charges of the electrons. But electrons have the ability to move
from atom to atom and this is what makes atoms bond together
to produce compounds. When an atom loses or gains one or
more electrons, it is called an ion. An ion with more electrons
than protons is a negative ion because the atom takes on a negative charge. If it has fewer electrons than protons, the atom
becomes a positive ion because it has a positive electrical
charge.
Look at a boron atom, which has the atomic number of 5. A
neutral Boron atom has 5 protons and 5 electrons. If it were to
lose electrons, it would become a positively charged ion. A
boron atom that has lost three electrons is written B3+. 3+ indicates it is a positive ion, missing three electrons. If it were written B3-, it would indicate that it had three additional electrons.
These symbols are called the oxidation numbers.
This seems complicated but it is really quite a simple system
developed by chemists to keep track of electrons. It is important
to remember that the number of protons in the nucleus doesn't
change.
NUCLEAR STABILITY
An atom is held together by the attraction between the positively charged protons in the nucleus and the negatively
charged electrons. But particles with the same electrical charges
repel each other. Why doesn't the nucleus fly apart? The reason
it holds together is because of the strong nuclear force, one of
the fundamental forces in the universe. This force operates
between the protons and neutrons at extremely short distances.
16
Elements with atomic numbers from 1 to 20 often have the
same number of neutrons and protons, but elements beyond 20
need increasing numbers of neutrons to hold the protons together. Beyond atomic number 83 no number of neutrons is sufficient to indefinitely hold the elements together.
When there are changes in the nucleus of an element, it is called
radioactive decay, or radiation. The original nucleus of an element decomposes to form a new nucleus and thus a different
element, releasing radiation in the process.
There are three types of radiation. Alpha radiation consists of
helium nuclei, 2 protons and 2 neutrons. Beta radiation consists
of high-speed electrons, and gamma rays are a very energetic
form of light, similar to X-rays. It is gamma rays that are particularly dangerous to humans and other life forms. Scientists
and technicians must be very cautious when they come into
contact with them.
But nuclear reactions are an essential and natural part of our
universe. The energy that we receive from the sun is the result
of fusion that occurs when two hydrogen atoms fuse together at
high temperatures. This releases energy that radiates outward as
electromagnetic energy that we call sunlight. Scientists are
working on harnessing fusion reactions because they are a
means of producing a virtually limitless, clean supply of energy.
We have even been able to create nuclear reactions ourselves by
splitting apart the nuclei of unstable atoms, such as uranium, in
a process called fission. This is the energy released in atomic
bombs and nuclear reactors.
QUANTUM THEORY
In the early part of the 20th century, scientists found it difficult
to understand the structure of atoms. Ernest Rutherford and his
colleagues visualized them as negatively charged electrons circulating about a positively charged nucleus. A German physicist named Max Planck suggested that energy emitted or absorbed by an object could only be emitted or absorbed in discrete amounts or units. He called these units of energy "quanta."
17
Niels Bohr, a Danish physicist, visualized atoms much like our
solar system with the nucleus like a sun and the electrons orbiting it like planets. This is called the planetary model. He then
applied Planck's idea of "quanta" to the behavior of the electrons surrounding the nucleus. He suggested that electrons' orbits depended on their amounts of energy. When an electron absorbs energy, it jumps from an orbit close to the nucleus to one
further away and when it moves closer to the nucleus it emits
energy. In both cases, the energy is only in discrete quantities.
Louis de Broglie, a French physicist, proposed that electrons
were not only particles but also a form of energy that acted in a
wavelike manner. But the more evidence that was gathered the
more scientists came to understand that atoms were not like the
solar system at all because the electrons did not circle the
nucleus in regular obits.
In one of the most significant developments, in 1927, Werner
Heisenberg, a German physicist, showed that it was impossible
to determine the precise location and velocity of an electron at
the same time. All that could be done was to describe the probability of the location of electrons. This has come to be called
the "Uncertainty Principle."
All of these ideas have come together into what is now called
Quantum Theory, or Quantum Mechanics, one of the most
important scientific advances of the 20th century. This theory
is fundamental to chemistry because the properties of elements
and the way they react with other elements depend on the
behavior of electrons.
ELECTRON BEHAVIOR
The Uncertainty Principle holds that it is impossible to know
the position and velocity of electrons at the same time. All we
can do is describe the probability that an electron might be
found within a certain region. However, electrons with a given
energy follow certain patterns around the nucleus. These are
called atomic orbitals.
18
Chemists picture the orbitals like clouds that are dense in areas
where the electron is more likely to be and less dense in others
where there is less probability of it being found. Each atomic
orbital may be described by a set of four quantum numbers.
The principal quantum number is called "n." As n increases in
value, the atomic orbitals become larger in size and the electrons are found further away from the nucleus. As atomic numbers of elements increase, they have electrons in these larger
orbitals and the size of the atom therefore increases. Orbitals of
lower principal quantum number have lower energy. The electrons first fill up the orbitals of lower energy before orbitals of
higher energy.
The second quantum number, L, refers to the shape of the
orbital. There are four important shapes, each with slightly different energy. All s-shaped orbitals are spherical, p are dumbbell shaped, and the d and f orbital shapes are more complicated, as shown in these drawings.
The third quantum number refers to the orientation of the
orbital. This refers only to the p-, d-, and f-shaped orbitals.
And finally, the fourth quantum number refers to the spin of the
electron. An electron can be thought of as spinning on its axis
in two possible directions. This means an orbital can only accommodate two electrons, each spinning in opposite directions.
So, the energy of an electron orbital is described by both the
principal quantum number, n, and the second quantum number,
L, together. As n increases, there is more than one orbital shape.
For example, where n is equal to 2, there are s- and p- shaped
orbitals. S orbitals have lower energy than p orbitals and fill
first. At n=3, d orbitals, with higher energies than p, fill last.
This diagram shows how the orbitals of the elements from 1 to
10 fill with electrons, filling the orbitals of lowest energy first.
The p orbitals take one electron each and after this, pairing
begins. This is repeated with all of the elements. It is called
Hund's Rule of Maximum Multiplicity.
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For example, look at oxygen, element 8. A neutral oxygen
atom has 8 electrons. The two in the first energy level are in the
s orbital and in the second energy level two are in s orbital.
Then, as the p orbitals are filled one electron goes into
each of
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the p orbitals and then the last electron pairs with p .
The electron configurations of atoms have a direct relationship
in how they interact with each other to create molecules and
compounds and all matter in the universe. With an understanding of the structure of atoms, and the behavior of electrons, it is
possible to predict with great accuracy how elements behave
and combine. This is one of the most remarkable achievements
of modern science.
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