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Chemistry Chapter 4 The Structure of the Atom

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Title: Chemistry Chapter 4 The Structure of the Atom Author: egeringer Last modified by: Erin Geringer Created Date: 9/28/2009 1:34:29 PM Document presentation format – PowerPoint PPT presentation

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Title: Chemistry Chapter 4 The Structure of the Atom


1
Chemistry Chapter 4 The Structure of the Atom
2
1.)Who was John Dalton?
  • An English schoolteacher (1766 1844) who
    reintroduced Democritus concept of atomos. He
    called the particles atoms.

3
2.)What are the main points of Daltons 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.

4
3.) What two laws helped Dalton to develop his
atomic theory?
  • Law of conservation of mass and law of multiple
    proportions.

5
4.) How does Daltons atomic theory explain the
Law of Conservation of Mass?
  • Daltons atomic theory explains the conservation
    of mass in chemical reactions as being the result
    of the separation, combination and rearrangement
    of atoms.

6
5.) How does Daltons atomic theory explain the
Law of Multiple Proportions?
  • Daltons 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
    Daltons theory

7
Defining the atom
8
6.) What is the current definition of an atom?
  • The smallest particle of an element that retains
    all of the properties of that element

9
7.) Is there an instrument that actually allows
us to see atoms?
  • The scanning tunneling microscope.

10
8.) Scientists are now able to manipulate
individual atoms. What field has this lead to?
  • Nanotechnology.
  • look at page 107

11
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 1900s

12
Discovering the Electron
13
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)

14
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.

15
11.) What were scientists convinced of by the
late 1800s concerning cathode rays?
  • That the cathode ray was a stream of charged
    particles with mass.

16
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.

17
13.) Who was J.J. Thomson?
  • An English physicist (1856 1940) who performed
    many experiments with the cathode ray tube.

18
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20
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)

21
15.) Why is this significant?
  • Because it means that atoms are divisible. Up
    until this point atoms were considered
    indivisible.

22
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?
23
  • 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.

24
17.) What development did Robert Millikan add to
atomic theory in 1909?
25
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.

26
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27
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

28
The Nuclear Atom
29
Our understanding of the nucleus came from
another accidental discovery. By understanding
radioactivity, the nucleus of the atom was
discovered.
30
( Not in your book) What did Henri Bequerel
discover in 1896?
31
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.

32
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33
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.
34
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.
35
20.) Who was Ernest Rutherford?
36
20.) Who was Ernest Rutherford?
  • A New Zealand Chemist/Physicist
  • (1871-1937)

37
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)

38
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
    (ß)
  • Continued next slide

39
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
    (?)

40
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/physics-
    iv/atoms-and-nuclei/rutherfords-experiment-animati
    on.php

41
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.

42
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.

43
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.

44
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.

45
22.) What was the name of Rutherfords model?
Draw an example.
  • The planetary model

46
  • 23.) Most of an atom is __empty ___ space.

47
24.) Who discovered the proton?
  • Henry Mosley, a worker in Rutherfords lab.
    Because of Moseley's work, the modern periodic
    table is based on the atomic numbers of the
    elements.

48
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.

49
26.) Who discovered the neutron?
  • An English physicist James Chadwich (1891-1974)
    Chadwich was a co-worker of Rutherford.

50
27.) What is a neutron?
  • The neutral particle in the nucleus of an atom.
    The nuetrons add stability to the nucleus.(strong
    nuclear force)

51
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
52
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.

53
Section 3 How Atoms Differ
54
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.

55
How many protons are in an atom of
  • Carbon?
  • Lead?
  • Iodine?
  • Mendelevium?
  • Calcium?

56
How many protons are in an atom of
  • Carbon- 6
  • Lead- 82
  • Iodine- 53
  • Mendelevium-101
  • Calcium- 20

57
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

58
In the following atoms how many electrons are
there?
  • Carbon?
  • Lead?
  • Iodine?
  • Mendelevium?
  • Calcium?

59
In the following atoms how many electrons are
there?
  • Carbon- 6
  • Lead- 82
  • Iodine- 53
  • Mendelevium-101
  • Calcium- 20

60
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.

61
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.

62
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.

63
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.
64
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?
65
  • 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.

66
For example
  • Chlorine exists as about 75 Cl-35 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.

67
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.

68
37.)What can the reported atomic mass tell us
about an element?
  • It tells you which isotope is most common.

69
Section 4 Unstable Nuclei and Radioactive Decay
70
38.)What are nuclear reactions?
  • Reactions that involve a change to the atoms
    nucleus.
  • Atoms of one element change into another type of
    element.
  • Radioactive substances emit radiation because the
    nucleus is unstable.

71
39.)What is considered to be the half-life of a
radioactive substance?
  • The amount of time it takes for ½ of the
    substance to change or decay into another
    substance.

72
40.)What are the three types of radiation?
  • Alpha (?)
  • Beta (ß)
  • Gamma (?)

73
41.)Complete the following table
Radiation type Symbol Mass (amu) charge
Alpha ? 4 2
Beta ß 1/1840 1-
gamma ? 0 0
74
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

75
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

76
42.)Alpha decay example
  • Write the nuclear reaction for the alpha decay of
    Europium - 152

77
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.

78
43.) Beta Decay example
  • What is the nuclear equation for the beta decay
    of carbon 14?

79
43.)Beta Decay example
  • What is the nuclear equation for the beta decay
    of Hydrogen-3?

80
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.
  • Contd next slide

81
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.
  • Contd next slide

82
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.
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