The document provides information about atomic structure and radioactivity. It begins by discussing early atomic models proposed by philosophers like Democritus. It then summarizes key developments in atomic theory, including Dalton's atomic theory and the experiments of Thomson, Rutherford, and Chadwick that led to the discovery of subatomic particles like electrons, protons, and neutrons. The document also discusses isotopes, radioactive decay, and the different types of nuclear radiation.

1. Chemistry
Toombs County High School

2.  The lab technician shown
here is using a magnifying
lens to examine a bacterial
culture in a petri dish.
When scientists cannot see
the details of what they
study, they try to obtain
experimental data that
help fill in the picture.

3. Early Models of the Atom
▪An atom is the smallest particle of an
element that retains its identity in a
chemical reaction.
▪Philosophers and scientists have
proposed many ideas on the structure of
atoms.

4.  Democritus’s Atomic Philosophy
 How did Democritus describe atoms?
Democritus

5.  Democritus believed that atoms were
indivisible and indestructible.
 Democritus’s ideas were limited
because they didn’t explain chemical
behavior and they lacked experimental
support.

6. Dalton’s AtomicTheory
▪How did John Dalton further
Democritus’s ideas on atoms?

7.  By using experimental methods, Dalton
transformed Democritus’s ideas on
atoms into a scientific theory.
 The result was Dalton’s atomic theory.

8. All elements are composed of tiny indivisible
particles called atoms.
4.1

9.  Atoms of the same element are identical.The
atoms of any one element are different from
those of any other element.
4.1

10.  Atoms of different elements can physically mix
together or can chemically combine in simple
whole-number ratios to form compounds.
4.1

11.  Chemical reactions occur when atoms are
separated, joined, or rearranged.Atoms
of one element are never changed into
atoms of another element in a chemical
reaction.
4.1

12. Sizing up the Atom
What instruments are used to
observe individual atoms?
4.1

13.  Despite their small size, individual
atoms are observable with instruments
such as scanning tunneling
microscopes.
4.1

14. ▪ Iron Atoms SeenThrough a Scanning Tunneling
Microscope
4.1

16.  Cathode-ray tubes are
found inTVs,
computer monitors,
and many other
devices with electronic
displays.
4.2

17.  Subatomic Particles
 What are three kinds of subatomic particles?
4.2

18. 4.2
Three kinds of subatomic
particles are electrons, protons,
and neutrons.

19.  Electrons
 In 1897, the English physicist J. J.
Thomson (1856–1940) discovered the
electron. Electrons are negatively
charged subatomic particles.
4.2

20. Thomson performed experiments that
involved passing electric current through
gases at low pressure.
The result was a glowing beam, or
cathode ray, that traveled from the
cathode to the anode.
4.2

21. ▪ Cathode RayTube
4.2

22. ▪ A cathode ray is deflected by a magnet.
4.2

23.  A cathode ray is deflected by electrically
charged plates.
4.2

24. Thomson concluded that a
cathode ray is a stream of
electrons. Electrons are parts of
the atoms of all elements.
4.2

25.  Protons and Neutrons
In 1886, Eugen Goldstein (1850–1930)
observed a cathode-ray tube and found rays
traveling in the direction opposite to that of
the cathode rays. He concluded that they
were composed of positive particles.
Such positively charged subatomic
particles are called protons.
4.2

26.  In 1932, the English physicist James
Chadwick (1891–1974) confirmed
the existence of yet another
subatomic particle: the neutron.
 Neutrons are subatomic particles
with no charge but with a mass
nearly equal to that of a proton.
4.2

27. ▪ Table 4.1 summarizes the properties of electrons,
protons, and neutrons.
4.2

28.  TheAtomic Nucleus
 How can you describe the structure of the nuclear
atom?
4.2

29.  J.J.Thompson and others supposed
the atom was filled with positively
charged material and the electrons
were evenly distributed throughout.
 This model of the atom turned out
to be short-lived, however, due to
the work of Ernest Rutherford
(1871–1937).
4.2

30.  Rutherford’s Gold-Foil Experiment
 In 1911, Rutherford and his coworkers
at the University of Manchester,
England, directed a narrow beam of
alpha particles at a very thin sheet of
gold foil.
4.2

31. ▪ Rutherford’sGold-Foil Experiment
4.2

32. ▪ Alpha particles scatter from the gold foil.
4.2

33.  The Rutherford Atomic Model
 Rutherford concluded that the atom is
mostly empty space.All the positive charge
and almost all of the mass are concentrated
in a small region called the nucleus.
 The nucleus is the tiny central core of an
atom and is composed of protons and
neutrons.
4.2

34.  In the nuclear atom, the protons
and neutrons are located in the
nucleus.
The electrons are distributed
around the nucleus and occupy
almost all the volume of the atom.
4.2

36.  Just as apples come in
different varieties, a
chemical element can
come in different
“varieties” called
isotopes.
4.3

37. 4.3
 Atomic Number
 What makes one element different from another?

38. 4.3
 Elements are different because they contain
different numbers of protons.
 The atomic number of an element is the
number of protons in the nucleus of an atom
of that element.

39. 4.3

42.  Mass Number
 How do you find the number of neutrons in an
atom?
4.3

43.  The total number of protons and neutrons in
an atom is called the mass number.
 The number of neutrons in an atom is the
difference between the mass number and atomic
number.
4.3

44. ▪ Au is the chemical symbol for gold.
4.3

47.  Isotopes
 How do isotopes of an element differ?
4.3

48. 4.3
 Isotopes are atoms that have the
same number of protons but
different numbers of neutrons.
 Because isotopes of an element have
different numbers of neutrons, they
also have different mass numbers.

49. ▪ Despite these differences, isotopes are chemically alike
because they have identical numbers of protons and
electrons.
4.3

52.  Atomic Mass
 How do you calculate the atomic mass of an
element?
4.3

53.  It is useful to to compare the relative masses
of atoms to a standard reference isotope.
Carbon-12 is the standard reference isotope.
Cabon-12 has a mass of exactly 12 atomic
mass units.
 An atomic mass unit (amu) is defined as one
twelfth of the mass of a carbon-12 atom.
4.3

54. ▪ Some Elements
andTheir Isotopes
4.3

55.  The atomic mass of an element is a weighted
average mass of the atoms in a naturally
occurring sample of the element.
 A weighted average mass reflects both the
mass and the relative abundance of the
isotopes as they occur in nature.
4.3

56. ▪ Weighted Average Mass of a ChlorineAtom
4.3

60. for Conceptual Problem 4.3

61.  To calculate the atomic mass of an element,
multiply the mass of each isotope by its natural
abundance, expressed as a decimal, and then add
the products.
4.3

62. ▪ For example, carbon has two stable isotopes:
▪ Carbon-12, which has a natural abundance of 98.89%, and
▪ Carbon-13, which has a natural abundance of 1.11%.
4.3

66.  The PeriodicTable—A Preview
 Why is a periodic table useful?
4.3

67.  A periodic table is an arrangement of
elements in which the elements are
separated into groups based on a set of
repeating properties.
 A periodic table allows you to easily
compare the properties of one element (or
a group of elements) to another element (or
group of elements).
4.3

68. ▪ The PeriodicTable
4.3

69.  Each horizontal row of the periodic table is
called a period.
 Within a given period, the properties of the
elements vary as you move across it from
element to element.
4.3

70. ▪ A Period
4.3

71.  Each vertical column of the periodic table is
called a group, or family.
 Elements within a group have similar
chemical and physical properties.
4.3

72. ▪ A Group or Family
4.3

74.  Marie Curie was a Polish
scientist whose research led
to many discoveries about
radiation and radioactive
elements. In 1934 she died
from leukemia caused by her
long-term exposure to
radiation.You will learn about
the various types of radiation
and their effects.
25.1

75.  Radioactivity
 How does an unstable nucleus release energy?
25.1

76.  Marie Curie (1867-1934) and Pierre Curie
(1859-1906) were able to show that rays
emitted by uranium atoms caused fogging in
photographic plates.
 Marie Curie named the process by which materials
give off such rays radioactivity.
 The penetrating rays and particles emitted by a
radioactive source are called radiation.
25.1

77.  Nuclear reactions differ from chemical
reactions in a number of important ways.
 In chemical reactions, atoms tend to attain stable
electron configurations by losing or sharing
electrons.
 In nuclear reactions, the nuclei of unstable
isotopes, called radioisotopes, gain stability by
undergoing changes.
25.1

78.  An unstable nucleus releases energy by
emitting radiation during the process of
radioactive decay.
25.1

79.  Types of Radiation
 What are the three main types of
nuclear radiation?
25.1

80. ▪ The three main types of nuclear radiation are alpha
radiation, beta radiation, and gamma radiation.
25.1

81.  Alpha Radiation
▪Alpha radiation consists of helium nuclei that have been
emitted from a radioactive source.These emitted particles,
called alpha particles, contain two protons and two
neutrons and have a double positive charge.
25.1

82.  Beta Radiation
▪ An electron resulting from the breaking apart of a
neutron in an atom is called a beta particle.
25.1

83.  Carbon-14 emits a beta particle as it undergoes
radioactive decay to form nitrogen-14.
25.1

84. 25.1

85. 25.1

86.  Gamma Radiation
▪ A high-energy photon emitted by a radioisotope is
called a gamma ray.The high-energy photons are
electromagnetic radiation.
25.1

87. ▪ Alpha particles are the least penetrating. Gamma rays
are the most penetrating.
25.1

88. 25.1

90.  Radon-222 is a radioactive isotope that is
present naturally in the soil in some areas. It
has a constant rate of decay.You will learn
about decay rates of radioactive substances.
25.2

91.  Nuclear Stability and Decay
 What determines the type of decay a radioisotope
undergoes?
25.2

92.  The nuclear force is an attractive force that
acts between all nuclear particles that are
extremely close together, such as protons
and neutrons in a nucleus
 At these short distances, the nuclear force
dominates over electromagnetic repulsions
and hold the nucleus together.
25.2

93.  More than 1,500 different nuclei are known.
Of those, only 264 are stable and do not
decay or change with time.These nuclei are
in a region called the band of stability.
25.2

94. 25.2

95.  The neutron-to-proton ratio determines the
type of decay that occurs.
 A positron is a particle with the mass of an
electron but a positive charge. During
positron emission, a proton changes to a
neutron.
25.2

96. 25.2

97.  Half-Life
 How much of a sample of a radioisotope remains
after each half-life?
25.2

98.  A half-life (t1/2) is the time required for one-
half of the nuclei of a radioisotope sample to
decay to products.
 After each half-life, half of the existing radioactive
atoms have decayed into atoms of a new element.
25.2

99. 25.2

100. 25.2

101. 25.2
Stable Isotope

102. ▪ The ratio of Carbon-
14 to stable carbon
in the remains of an
organism changes
in a predictable way
that enables the
archaeologist to
obtain an estimate
of its age.
25.2

105.  Transmutation Reactions
 What are two ways that transmutation can occur?
25.2

106.  The conversion of an atom of one element to
an atom of another element is called
transmutation.
 Transmutation can occur by radioactive decay.
Transmutation can also occur when particles
bombard the nucleus of an atom.
25.2

107. ▪ The first artificial transmutation reaction involved
bombarding nitrogen gas with alpha particles.
25.2

108. ▪ The elements in the periodic table with atomic numbers above
92, the atomic number of uranium, are called the
transuranium elements.
All transuranium elements undergo transmutation.
None of the transuranium elements occur in nature, and all of
them are radioactive.
25.2

109. ▪ Transuranium elements are synthesized in nuclear
reactors and nuclear accelerators.
25.2

111.  The sun is not actually
burning. If the energy given
off by the sun were the
product of a combustion
reaction, the sun would have
burned out approximately
2000 years after it was
formed, long before today.
You will learn how energy is
produced in the sun.
25.3

112.  Nuclear Fission
 What happens in a nuclear chain reaction?
25.3

113.  When the nuclei of certain isotopes
are bombarded with neutrons, they
undergo fission, the splitting of a
nucleus into smaller fragments.
25.3

114.  In a chain reaction, some of the
neutrons produced react with other
fissionable atoms, producing more
neutrons which react with still more
fissionable atoms.
25.3

115. ▪ Nuclear Fission
25.3

116. 25.3
A Nuclear Power Plant

117.  Neutron Moderation
▪ Neutron moderation is a process that slows down
neutrons so the reactor fuel (uranium-235 or plutonium-
239) captures them to continue the chain reaction.
25.3

118.  Neutron Absorption
▪ Neutron absorption is a process that decreases the
number of slow-moving neutrons. Control rods, made of
a material such a cadmium, are used to absorb neutrons.
25.3

119.  NuclearWaste
 Why are spent fuel rods from a nuclear reaction
stored in water?
25.3

120.  Water cools the spent rods, and also acts as a
radiation shield to reduce the radiation levels.
25.3

121.  Nuclear Fusion
 How do fission reactions and fusion reactions
differ?
25.3

122. ▪ Fusion occurs when nuclei combine to produce a
nucleus of greater mass. In solar fusion, hydrogen nuclei
(protons) fuse to make helium nuclei and two positrons.
25.3

123.  Fusion reactions, in which small nuclei combine,
release much more energy than fission reactions,
in which large nuclei split.
25.3

124.  The use of controlled fusion as an energy
source on Earth is appealing.
 The potential fuels are inexpensive and readily
available.
 The problems with fusion lie in achieving the high
temperatures necessary to start the reaction and
in containing the reaction once it has started.
25.3

126.  In a smoke detector, radiation
from the Americum nuclei ionizes
the nitrogen and oxygen in smoke-
free air, allowing a current to flow.
When smoke particles get in the
way, a drop in current is detected
by an electronic circuit, causing it
to sound an alarm.You will learn
about some of the other practical
uses of radiation.
25.4

127.  Detecting Radiation
 What are three devices used to detect radiation?
25.4

128. ▪ Ionizing radiation is radiation with enough energy to
knock electrons off some atoms of the bombarded
substance to produce ions.
▪ Devices such as Geiger counters, scintillation counters, and film
badges are commonly used to detect radiation.
25.4

129. ▪ Radiation can produce ions, which can then be detected,
or it can expose a photographic plate and produce
images.
25.4

130.  Geiger Counter
▪ A Geiger counter uses a gas-filled metal tube to detect
radiation.
25.4

131.  Scintillation Counter
▪ A scintillation counter uses a phosphor-coated surface
to detect radiation.
25.4

132.  Film Badge
▪ A film badge consists of several layers of photographic
film covered with black lightproof paper, all encased in a
plastic or metal holder.
25.4

133.  Using Radiation
 How are radioisotopes used in medicine?
25.4

134.  Neutron activation analysis is a procedure
used to detect trace amounts of elements in
samples.
 Neutron activation analysis is used by
museums to detect art forgeries, and by
crime laboratories to analyze gunpowder
residues.
25.4

135.  Radioisotopes can be used to diagnose medical
problems and, in some cases, to treat diseases.
25.4

136. ▪ This scanned image of a thyroid gland shows where
radioactive iodine-131 has been absorbed.
25.4