Title: Chemistry: Matter and Change
1CHEMISTRY Matter and Change
Chapter 4 The Structure of the Atom
2Table Of Contents
CHAPTER4
Section 4.1 Early Ideas About Matter Section
4.2 Defining the Atom Section 4.3 How Atoms
Differ Section 4.4 Unstable Nuclei and
Radioactive Decay
Click a hyperlink to view the corresponding
slides.
Exit
3Early Ideas About Matter
SECTION4.1
- Compare and contrast the atomic models of
Democritus, Aristotle, and Dalton.
- Understand how Dalton's theory explains the
conservation of mass.
theory an explanation supported by many
experiments is still subject to new experimental
data, can be modified, and is considered
successful if it can be used to make predictions
that are true
4Early Ideas About Matter
SECTION4.1
Dalton's atomic theory
The ancient Greeks tried to explain matter, but
the scientific study of the atom began with John
Dalton in the early 1800's.
5Early Ideas About Matter
SECTION4.1
Greek Philosophers
- Many ancient scholars believed matter was
composed of such things as earth, water, air, and
fire.
- Many believed matter could be endlessly divided
into smaller and smaller pieces.
6Early Ideas About Matter
SECTION4.1
Greek Philosophers (cont.)
- Democritus (460370 B.C.) was the first person to
propose the idea that matter was not infinitely
divisible, but made up of individual particles
called atomos, from which the English word atom
is derived.
- Aristotle (484322 B.C.) disagreed with
Democritus because he did not believe empty space
could exist. - Aristotles views went unchallenged for 2,000
years until science developed methods to test the
validity of his ideas.
7Early Ideas About Matter
SECTION4.1
Greek Philosophers (cont.)
8Early Ideas About Matter
SECTION4.1
Greek Philosophers (cont.)
- John Dalton revived the idea of the atom in the
early 1800s based on numerous chemical reactions.
- Daltons atomic theory easily explained
conservation of mass in a reaction as the result
of the combination, separation, or rearrangement
of atoms.
9Early Ideas About Matter
SECTION4.1
Greek Philosophers (cont.)
10Section Check
SECTION4.1
Who was the first person to propose the idea that
matter was not infinitely divisible?
A. Aristotle B. Plato C. Dalton D. Democritus
11Section Check
SECTION4.1
Daltons theory also conveniently explained
what? A. the electron B. the nucleus C. law of
conservation of mass D. law of Democritus
12(No Transcript)
13Defining the Atom
SECTION4.2
- Distinguish between the subatomic particles in
terms of relative charge and mass. - Describe the structure of the atom, including the
locations of the subatomic particles.
model a visual, verbal, and/or mathematical
explanation of data collected from many
experiments
14Defining the Atom
SECTION4.2
atom cathode ray electron nucleus proton neutron
An atom is made of a nucleus containing protons
and neutrons electrons move around the nucleus.
15Defining the Atom
SECTION4.2
The Atom
- The smallest particle of an element that retains
the properties of the element is called an atom.
- An instrument called the scanning tunneling
microscope (STM) allows individual atoms to be
seen.
16Defining the Atom
SECTION4.2
The Electron
- When an electric charge is applied, a ray of
radiation travels from the cathode to the anode,
called a cathode ray.
- Cathode rays are a stream of particles carrying a
negative charge. - The particles carrying a negative charge are
known as electrons.
17Defining the Atom
SECTION4.2
The Electron (Cont.)
- This figure shows a typical cathode ray tube.
18Defining the Atom
SECTION4.2
The Electron (Cont.)
- J.J. Thomson measured the effects of both
magnetic and electric fields on the cathode ray
to determine the charge-to-mass ratio of a
charged particle, then compared it to known
values.
- The mass of the charged particle was much less
than a hydrogen atom, then the lightest known
atom. - Thomson received the Nobel Prize in 1906 for
identifying the first subatomic particlethe
electron
19Defining the Atom
SECTION4.2
The Electron (Cont.)
- In the early 1910s, Robert Millikan used the
oil-drop apparatus shown below to determine the
charge of an electron.
20Defining the Atom
SECTION4.2
The Electron (Cont.)
- Charges change in discrete amounts1.602 ? 1019
coulombs, the charge of one electron (now
equated to a single unit, 1).
- With the electrons charge and charge-to-mass
ratio known, Millikan calculated the mass of a
single electron.
21Defining the Atom
SECTION4.2
The Electron (Cont.)
- Matter is neutral. You know that matter is
neutral from everyday experiences. You do not
receive an electric shock (except under certain
conditions) when you touch an object. - If electrons are negative, then how is matter,
which is made up of electrons, neutral? - J.J. Thomson proposed a model of the atom to
answer this question.
22Defining the Atom
SECTION4.2
The Electron (Cont.)
- J.J. Thomson's plum pudding model of the atom
states that the atom is a uniform, positively
charged sphere containing electrons.
23Defining the Atom
SECTION4.2
The Nucleus
- In 1911, Ernest Rutherford studied how positively
charged alpha particles interacted with solid
matter.
- By aiming the particles at a thin sheet of gold
foil, Rutherford expected the paths of the alpha
particles to be only slightly altered by a
collision with an electron.
24Defining the Atom
SECTION4.2
The Nucleus (cont.)
- Although most of the alpha particles went through
the gold foil, a few of them bounced back, some
at large angles.
25Defining the Atom
SECTION4.2
The Nucleus (cont.)
- Rutherford concluded that atoms are mostly empty
space.
- Almost all of the atom's positive charge and
almost all of its mass is contained in a dense
region in the center of the atom called the
nucleus. - Electrons are held within the atom by their
attraction to the positively charged nucleus.
26Defining the Atom
SECTION4.2
The Nucleus (cont.)
- The repulsive force between the positively
charged nucleus and positive alpha particles
caused the deflections.
27Defining the Atom
SECTION4.2
The Nucleus (cont.)
- Rutherford refined the model to include
positively charged particles in the nucleus
called protons.
- James Chadwick received the Nobel Prize in 1935
for discovering the existence of neutrons,
neutral particles in the nucleus which accounts
for the remainder of an atoms mass.
28Defining the Atom
SECTION4.2
The Nucleus (cont.)
- All atoms are made of three fundamental subatomic
particles the electron, the proton, and the
neutron.
- Atoms are spherically shaped.
- Atoms are mostly empty space, and electrons
travel around the nucleus held by an attraction
to the positively charged nucleus.
29Defining the Atom
SECTION4.2
The Nucleus (cont.)
- Scientists have determined that protons and
neutrons are composed of subatomic particles
called quarks.
30Defining the Atom
SECTION4.2
The Nucleus (cont.)
- Scientists do not yet understand if or how quarks
affect chemical behavior. - Chemical behavior can be explained by considering
only an atom's electrons.
31Section Check
SECTION4.2
Atoms are mostly ____. A. positive B. negative
C. solid spheres D. empty space
32Section Check
SECTION4.2
What are the two fundamental subatomic particles
found in the nucleus? A. proton and electron
B. proton and neutron C. neutron and electron
D. neutron and positron
33(No Transcript)
34How Atoms Differ
SECTION4.3
- Explain the role of atomic number in determining
the identity of an atom.
- Define an isotope.
- Explain why atomic masses are not whole numbers.
- Calculate the number of electrons, protons, and
neutrons in an atom given its mass number and
atomic number.
35How Atoms Differ
SECTION4.3
periodic table a chart that organizes all known
elements into a grid of horizontal rows (periods)
and vertical columns (groups or families)
arranged by increasing atomic number
atomic number isotopes mass number
atomic mass unit (amu) atomic mass
The number of protons and the mass number define
the type of atom.
36How Atoms Differ
SECTION4.3
Atomic Number
- Each element contains a unique positive charge in
their nucleus.
- The number of protons in the nucleus of an atom
identifies the element and is known as the
elements atomic number.
37How Atoms Differ
SECTION4.3
Isotopes and Mass Number
- All atoms of a particular element have the same
number of protons and electrons but the number of
neutrons in the nucleus can differ.
- Atoms with the same number of protons but
different numbers of neutrons are called isotopes.
38How Atoms Differ
SECTION4.3
Isotopes and Mass Number (Cont.)
- In nature, most elements are found as mixtures of
isotopes. Usually, the relative abundance of
each isotope is constant. - Ex. In a banana, 93.26 is potassium-39, 6.73 is
potassium-41 and 0.01 is potassium-40. In
another banana or in a different source of
potassium, the percentage composition of the
potassium isotopes will still be the same.
- Isotopes containing more neutrons have a greater
mass. - Isotopes of an atom have the same chemical
behavior.
39How Atoms Differ
SECTION4.3
Isotopes and Mass Number (Cont.)
- The mass number is the sum of the protons and
neutrons in the nucleus.
40How Atoms Differ
SECTION4.3
Mass of Atoms
- One atomic mass unit (amu) is defined as 1/12th
the mass of a carbon-12 atom.
- One amu is nearly, but not exactly, equal to one
proton and one neutron.
41How Atoms Differ
SECTION4.3
Mass of Atoms (cont.)
- The atomic mass of an element is the weighted
average mass of the isotopes of that element.
42Section Check
SECTION4.3
An unknown element has 19 protons, 19 electrons,
and 3 isotopes with 20, 21 and 22 neutrons. What
is the elements atomic number? A. 38 B. 40
C. 19 D. unable to determine
43Section Check
SECTION4.3
Elements with the same number of protons and
differing numbers of neutrons are known as what?
A. isotopes B. radioactive C. abundant
D. ions
44(No Transcript)
45SECTION4.4
Unstable Nuclei and Radioactive Decay
- Explain the relationship between unstable nuclei
and radioactive decay.
- Characterize alpha, beta, and gamma radiation in
terms of mass and charge.
element a pure substance that cannot be broken
down into simpler substances by physical or
chemical means
46SECTION4.4
Unstable Nuclei and Radioactive Decay
radioactivity radiation nuclear
reaction radioactive decay alpha radiation
alpha particle nuclear equation beta
radiation beta particle gamma rays
Unstable atoms emit radiation to gain stability.
47SECTION4.4
Unstable Nuclei and Radioactive Decay
Radioactivity
- Nuclear reactions can change one element into
another element.
- In the late 1890s, scientists noticed some
substances spontaneously emitted radiation, a
process they called radioactivity. - The rays and particles emitted are called
radiation. - A reaction that involves a change in an atom's
nucleus is called a nuclear reaction.
48SECTION4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay
- Unstable nuclei lose energy by emitting radiation
in a spontaneous process called radioactive decay.
- Unstable radioactive elements undergo radioactive
decay thus forming stable nonradioactive elements.
49SECTION4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay (cont.)
- Alpha radiation is made up of positively charged
particles called alpha particles.
- Each alpha particle contains two protons and two
neutrons and has a 2 charge.
50SECTION4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay (cont.)
- The figure shown below is a nuclear equation
showing the radioactive decay of radium-226 to
radon-222.
4 He 2
- An alpha particle is equivalent to a helium-4
nucleus and is represented by 4He or . - Thus, showing mass is conserved in a nuclear
equation.
2
51SECTION4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay (cont.)
- Beta radiation is radiation that has a negative
charge and emits beta particles.
- Each beta particle is an electron with a 1
charge. - During Beta decay, a neutron is converted to a
proton and an electron. The electron is emitted
and the proton stays in the nucleus.
52SECTION4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay (cont.)
53SECTION4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay (cont.)
- Gamma rays are high-energy radiation with no mass
and are neutral. - They usually accompany alpha and beta radiation.
- Gamma rays account for most of the energy lost
during radioactive decay.
54SECTION4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay (cont.)
- Because gamma rays are massless, the emission of
gamma rays by themselves cannot result in the
formation of a new atom.
55SECTION4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay (cont.)
- Atoms that contain too many or two few neutrons
are unstable and lose energy through radioactive
decay to form a stable nucleus.
- Few exist in naturemost have already decayed to
stable forms.
56Section Check
SECTION4.4
A reaction that changes one element into another
in the nucleus of an atom is called what?
A. chemical reaction B. beta radiation
C. nuclear reaction D. physical reaction
57Section Check
SECTION4.4
Why are radioactive elements rare in nature?
A. They do no occur on Earth. B. Most have
already decayed to a stable form. C. They take
a long time to form. D. They are too hard to
detect.
58(No Transcript)
59CHAPTER4
The Structure of the Atom
Resources
Chemistry Online Study Guide Chapter
Assessment Standardized Test Practice
60Early Ideas About Matter
SECTION4.1
Study Guide
Key Concepts
- Democritus was the first person to propose the
existence of atoms.
- According to Democritus, atoms are solid,
homogeneous, and indivisible. - Aristotle did not believe in the existence of
atoms. - John Daltons atomic theory is based on numerous
scientific experiments.
61Defining the Atom
SECTION4.2
Study Guide
Key Concepts
- An atom is the smallest particle of an element
that maintains the properties of that element.
- Electrons have a 1 charge, protons have a 1
charge, and neutrons have no charge. - An atom consists mostly of empty space
surrounding the nucleus.
62How Atoms Differ
SECTION4.3
Study Guide
Key Concepts
- The atomic number of an atom is given by its
number of protons. The mass number of an atom is
the sum of its neutrons and protons.
- atomic number number of protons number of
electrons - mass number atomic number number of neutrons
- Atoms of the same element with different numbers
of neutrons are called isotopes. - The atomic mass of an element is a weighted
average of the masses of all of its naturally
occurring isotopes.
63Unstable Nuclei and Radioactive Decay
SECTION4.4
Study Guide
Key Concepts
- Chemical reactions involve changes in the
electrons surrounding the nucleus of an atom.
Nuclear reactions involve changes in the nucleus
of an atom.
- There are three types of radiation alpha (charge
of 2), beta (charge of 1), and gamma (no
charge). - The neutron-to-proton ratio of an atoms nucleus
determines its stability.
64CHAPTER4
The Structure of the Atom
Chapter Assessment
Whose work led to the modern atomic theory?
A. Dalton B. Rutherford C. Einstein
D. Aristotle
65CHAPTER4
The Structure of the Atom
Chapter Assessment
Which particle is not found in the nucleus of an
atom? A. neutron B. proton C. gamma ray
D. electron
66CHAPTER4
The Structure of the Atom
Chapter Assessment
Two isotopes of an unknown element have the same
number of A. protons B. neutrons
C. electrons D. both A and C
67CHAPTER4
The Structure of the Atom
Chapter Assessment
Lithium has an atomic mass of 6.941 and two
isotopes, one with 6 neutrons and one with 7
neutrons. Which isotope is more abundant?
A. 6Li B. 7Li C. Both isotopes occur equally.
D. unable to determine
68CHAPTER4
The Structure of the Atom
Chapter Assessment
What happens when an element emits radioactive
particles? A. It gains energy. B. It gains
neutrons. C. It loses stability. D. It loses
energy.
69CHAPTER4
The Structure of the Atom
Standardized Test Practice
What is the smallest particle of an element that
still retains the properties of that element?
A. proton B. atom C. electron D. neutron
70CHAPTER4
The Structure of the Atom
Standardized Test Practice
How many neutrons, protons, and electrons does
12454Xe have? A. 124 neutrons, 54 protons, 54
electrons B. 70 neutrons, 54 protons, 54
electrons C. 124 neutrons, 70 protons, 54
electrons D. 70 neutrons, 70 protons, 54
electrons
71CHAPTER4
The Structure of the Atom
Standardized Test Practice
The primary factor in determining an atom's
stability is its ratio of neutrons to ____.
A. protons B. electrons C. alpha
particles D. isotopes
72CHAPTER4
The Structure of the Atom
Standardized Test Practice
What is the densest region of an atom?
A. electron cloud B. nucleus C. isotopes
D. atomic mass
73CHAPTER4
The Structure of the Atom
Standardized Test Practice
Why are electrons attracted to the cathode in a
cathode ray tube? A. The cathode is more
stable. B. The cathode has a positive charge.
C. The cathode has a negative charge. D. The
cathode has no charge.
74This slide is intentionally blank.