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Chemistry Chapter 4
The Structure of the Atom
1.)Who was John Dalton?
An
English schoolteacher
(1766 – 1844) who
reintroduced Democritus’
concept of atomos. He called
the particles atoms.
2.)What are the main points of
Dalton’s atomic theory?
 All
matter is composed of extremely
small particles called atoms.
 All atoms of a given element are
identical
 Atoms cannot be created, divided or
destroyed
 Different atoms combine in simple
whole ratios to form compounds
 In a chemical reaction, atoms are
separated, combined and
rearranged.
3.) What two laws helped Dalton to
develop his atomic theory?
Law
of conservation of mass
and law of multiple
proportions.
4.) How does Dalton’s atomic theory
explain the Law of Conservation
of Mass?
 Dalton’s
atomic theory explains
the conservation of mass in
chemical reactions as being the
result of the separation,
combination and rearrangement
of atoms.
5.) How does Dalton’s atomic theory
explain the Law of Multiple
Proportions?
 Dalton’s
theory states that
atoms combine in simple whole
number ratios to form
compounds. This explains why
two compounds made of the
same compounds have
combinations of atoms in simple
whole number ratios. Atoms are
not divisible in Dalton’s theory
Defining the atom
6.) What is the current definition of
an atom?
The
smallest particle of an
element that retains all of the
properties of that element
7.) Is there an instrument that
actually allows us to “see”
atoms?
The
scanning tunneling
microscope.
8.) Scientists are now able to
manipulate individual atoms.
What field has this lead to?
Nanotechnology.
look
at page 107
9.) Approximately what year was it
when scientists began to
understand the composition of the
atom?
 The
greatest increase in
understanding was around the
early 1900’s
Discovering the Electron
10.) What is the cathode ray tube?
A
partially evacuated glass
tube filled with low pressure
gas. On one side of the tube
is a positively charged
cathode and on the other side
is a negatively charged
anode. (continued next slide)
10.) What is the cathode ray tube?
When
an electric current is
passed through the tube a
colored beam can be seen
where the electricity is. The
cathode ray tube allowed
scientists to “see” electricity.
11.) What were scientists convinced
of by the late 1800’s concerning
cathode rays?
That
the cathode ray
was a stream of charged
particles with mass.
12.) How did they make this
conclusion?
They
knew the stream was
charged because the cathode
ray could be moved with a
charged electric plates and
magnets. They knew it had
mass because the stream
could spin a paddle wheel.
13.) Who was J.J. Thomson?
An
English physicist
(1856– 1940) who
performed many
experiments with the
cathode ray tube.
14.) What did J.J. Thomson
determine after his experiments
with the cathode ray tube?
 He
determined the ratio of
charge to mass. He found the
charge in coulombs of a gram of
electrons. He also concluded that
the mass of the individual
charged particle was much less
than the mass of the smallest
atom (hydrogen)
15.) Why is this significant?
Because
it means that
atoms are divisible. Up
until this point atoms were
considered indivisible.
16.) How did J.J. Thomson address
the problem that matter for the
most part is neutral, and yet there
existed negatively charged
particles he called electrons?
 He
proposed the Plum Pudding
model of the atom. The model he
used to describe the atom had a
positively charged background
and electrons scattered
throughout. This way there could
be negatively charged particles
with the entire atom being
neutral.
17.) What development did Robert
Millikan add to atomic theory in
1909?
17.) What development did Robert
Millikan add to atomic theory in
1909?
 Robert
Millikan discovered the
charge on a single electron. His
experiment was called the oil
droplet experiment.
18.) J.J. Thomson knew the charge
on a gram of electrons. Once
Millikan determined the charge
on a single electron, he could
calculate the mass of a single
electron. What did Millikan
determine the mass of a single
electron to be?
 9.1
x 10-28 gram. This is 1/1840
the mass of a hydrogen atom
The Nuclear Atom
Our understanding of the nucleus
came from another accidental
discovery. By understanding
radioactivity, the nucleus of the atom
was discovered.
( Not in your book) What did Henri
Bequerel discover in 1896?
19.)( Not in your book) What did
Henri Bequerel discover in 1896?
 Henri
Bequerel placed a piece of
uranium on top of an envelope of
undeveloped film. Because the
exact image of the rock was
exposed on the film, Bequerel
knew that some sort of radiation
was coming from the uranium.
Radioactivity was discovered.
For the next 20 to 30 years many
scientists worked with radioactive
substances in order to have a better
understanding of radioactivity. Pierre
and Marie Curie were well known for
their work with radioactive
substances. They discovered both
Radium and Polonium.
Ernest Rutherford is well known for
his work with radioactivity. There are
two experiments that he performed
that are especially significant. We
will learn about them both.
20.) Who was Ernest Rutherford?
20.) Who was Ernest Rutherford?
A
New Zealand
Chemist/Physicist
(1871-1937)
24.) Describe the experiment in
which Rutherford discovered the
three types of radiation.
 Rutherford
placed a chunk of
radioactive substance in a lead
block. He directed the radiation
through one side of the block. He
then used charged plates to
determine the charge of
radiation.
(continued next slide)
24.) Describe the experiment in
which Rutherford discovered the
three types of radiation.
 He
realized that there were
three types of radiation.
 The negatively charged
radiation was attracted to the
postive plate. He called these
beta particles (β)
Continued next slide
24.) Describe the experiment in
which Rutherford discovered the
three types of radiation.
 The
positively charged
radiation was attracted to the
negative plate. He called
these alpha particles (⍺)
 The nuetral particles were unaffected
by the charged plates. He called
these gamma particles (ɣ)
21.) In 1911 Rutherford designed the
alpha scattering experiment.
Describe this experiment. How
did what actually happened in
this experiment compare to what
Rutherford expected to happen?
What did this tell Rutherford
about the structure of the atom?

http://www.tutorvista.com/content/physics/physicsiv/atoms-and-nuclei/rutherfords-experiment-animation.php
21.) Slide 1 of 4
 Rutherford
wanted to know
how alpha particles
interacted with a solid. He
placed an alpha emitter in a
lead block and aimed it at a
piece of gold foil. He either
expected all of the particles
to travel through with a small
amount of deflection or all of
them to bounce back.
21.) Slide 2 of 4
 What
happened was that
most of the particles went
straight through. Some were
slightly deflected and VERY
RARELY a particle completely
reversed direction.
21.) Slide 3 of 4
 When
most of the particles
went straight through it
meant that an atom is mainly
empty space. When rarely, an
alpha particle was completely
reversed, it meant that the
concentration of positive
charge was in a very small
area.
21.) Slide 4 of 4
 Rutherford
called this area
the nucleus. He proposes that
almost all of the mass in the
nucleus and that electrons
orbit the nucleus like planets
orbit the sun.
22.) What was the name of Rutherford’s
model? Draw an example.
 The
planetary model
23.) Most of an atom is
__empty ___ space.
24.) Who discovered the proton?
 Henry
Mosley, a worker in
Rutherford’s lab. Because of
Moseley's work, the modern
periodic table is based on the
atomic numbers of the elements.
25.) What are protons?
The
positively charged
particle in the nucleus of an
atom. The number of protons
determines which element an
atom is. The charge on the
proton is exactly equal to, but
opposite the charge of the
electron.
26.) Who discovered the neutron?

An English physicist James Chadwich
(1891-1974) Chadwich was a co-worker of
Rutherford.
27.) What is a neutron?
The
neutral particle
in the nucleus of an
atom. The nuetrons
add stability to the
nucleus.(strong
nuclear force)
Fill in the table
Particle
Symbol
Location
Relative
charge
Relative
mass
Electron
e-
Outside
nucleus
1-
0
(1/1840)
Proton
P+
Inside
nucleus
1+
1 amu
Nuetron
n0
Inside
Nucleus
0
1 amu
29.) What is our concept of the atom
today?

Our currently accepted model is the
electron cloud model. Electrons are in
regions around the nucleus called the
electron cloud. Where the cloud is
most dense the probability of finding
an electron is greatest. The nucleus
contains the protons, neutrons and
most of the mass. All atoms are
nuetral. The number of protons is
equal to the number of electrons.
Section 3: How Atoms Differ
30.) What is atomic number?
It
is the number of
protons in the nucleus of
an atom. All atoms of a
given element have the
same atomic number.
How many protons are in an atom of :
Carbon?
 Lead?
 Iodine?
 Mendelevium?
 Calcium?

How many protons are in an atom of :
Carbon- 6
 Lead- 82
 Iodine- 53
 Mendelevium-101
 Calcium- 20

31.) In an atom, how does the atomic
number relate to the number of
electrons?
 In
an atom the number of
protons is equal to number of
electrons
In the following atoms how many
electrons are there?
 Carbon?
 Lead?
 Iodine?
 Mendelevium?
 Calcium?
In the following atoms how many
electrons are there?
 Carbon-
6
 Lead- 82
 Iodine- 53
 Mendelevium-101
 Calcium- 20
32.) What is an isotope?
Atoms
of the same
element with different
numbers of neutrons. All
atoms of any element
have the same number of
protons. Isotopes have
the same number of
protons but different
numbers of neutrons.
33.) What is the mass number?
 The
mass number is the sum
of the number of protons and
neutrons. The number of
neutrons can be determined
by subtracting the number of
protons (atomic number)
from the mass number.
34.) What is the atomic mass unit
(amu)?
1
atomic mass unit is the
mass of 1/12 the mass of a
single carbon 12 atom.
 Carbon-12 has 6 protons and
6 neutrons.
Scientists could have chosen any
isotope to use to define the atomic
mass unit. There is nothing special
about the carbon 12 isotope. It is just
the isotope they chose.
35.) On the periodic table you will
notice that a lot of the atomic
masses listed have decimals. If
the mass is determined by the
number of neutrons and protons,
which are 1 amu each, how can
there be decimal values?
Because
the masses listed
are a weighted average of
all of the isotopes that
exist. Also, a proton and
neutron are exactly equal
in mass.
For example
 Chlorine
exists as about 75% Cl35 and 25% Cl -37.
 (35) (.75) + (37)(.25) = 35.5

(Mass #)(% abundance) + (mass #)(%abundance)
 The
weighted average is always
closer to the isotope with the
greatest percent abundance.
36.)How do you calculate the
weighted atomic mass of
different isotopes of the same
element?
Multiply
the mass of each
isotope by its % abundance
and add the results.
37.)What can the reported atomic
mass tell us about an element?
It
tells you which isotope is
most common.
Section 4: Unstable Nuclei and
Radioactive Decay
38.)What are nuclear reactions?
Reactions
that involve a
change to the atom’s
nucleus.
Atoms of one element change
into another type of element.
Radioactive substances emit
radiation because the nucleus
is unstable.
39.)What is considered to be the halflife of a radioactive substance?
The
amount of time it takes
for ½ of the substance to
change or decay into another
substance.
40.)What are the three types of
radiation?
Alpha
(⍺)
Beta (β)
Gamma (Ɣ)
41.)Complete the following table
Radiation
type
Symbol
Mass
(amu)
charge
Alpha
⍺
4
2+
Beta
β
1/1840
1-
gamma
Ɣ
0
0
42.)Describe alpha radiation
An
alpha particle is
ejected from the nucleus.
Since the alpha particle is
made up of 2 protons and
2 neutrons the mass # is
decreased by 4 amu.
Continued next slide
42.)Describe alpha radiation
 Because
the type of element
is determined by the number
of protons, the element
changes to an element with
two less protons(atomic #
decreases by 2)
 Continued next slide
42.)Alpha decay example

Write the nuclear reaction for the alpha
decay of Europium - 152
43.)Describe beta radiation.
 With
beta radiation, an
electron is ejected from the
nucleus and a nuetron
becomes a proton.
 The mass number stays the
same, but the atomic number
increases by one.
43.) Beta Decay example
 What
is the nuclear equation for
the beta decay of carbon 14?
43.)Beta Decay example
 What
is the nuclear equation for
the beta decay of Hydrogen-3?
44.)Describe gamma radiation
 This
is the most dangerous type
of radiation.
 Gamma radiation usually
accompanies alpha and beta
radiation.
 Gamma radiation accounts for
most of the energy lost during
radioactive decay.
 Cont’d next slide
44.) Describe gamma radiation
The
emission of gamma rays
by themselves do not create
new atoms.
We will not have nuclear
equation for gamma decay.
Cont’d next slide
48.)What is the reason that radiation
occurs?
The
primary factor is the
stability of the atom which is
the result of the proton to
neutron ratio
Unstable nuclei lose energy
through radioactive decay to
produce a more stable
nucleus.