John Dalton (1766-1844), an English schoolteacher and chemist, studied the results of experiments by many other scientists. - PowerPoint PPT Presentation

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John Dalton (1766-1844), an English schoolteacher and chemist, studied the results of experiments by many other scientists.

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Title: John Dalton (1766-1844), an English schoolteacher and chemist, studied the results of experiments by many other scientists.


1
Atomic Structure Basic Concepts
Topic 2
Daltons Atomic Theory
  • John Dalton (1766-1844), an English schoolteacher
    and chemist, studied the results of experiments
    by many other scientists.

2
Atomic Structure Basic Concepts
Topic 2
Daltons Atomic Theory
  • Dalton proposed his atomic theory of matter in
    1803.
  • Although his theory has been modified slightly to
    accommodate new discoveries, Daltons theory was
    so insightful that it has remained essentially
    intact up to the present time.

3
Atomic Structure Basic Concepts
Topic 2
Daltons Atomic Theory
  • The following statements are the main points of
    Daltons atomic theory.

1. All matter is made up of atoms.
2. Atoms are indestructible and cannot be
divided into smaller particles. (Atoms are
indivisible.)
3. All atoms of one element are exactly
alike, but are different from atoms of
other elements.
4
Atomic Structure Basic Concepts
Topic 2
The Electron
  • Because of Daltons atomic theory, most
    scientists in the 1800s believed that the atom
    was like a tiny solid ball that could not be
    broken up into parts.
  • In 1897, a British physicist, J.J. Thomson,
    discovered that this solid-ball model was not
    accurate.
  • Thomsons experiments used a vacuum tube.

5
Atomic Structure Basic Concepts
Topic 2
The Electron
  • A vacuum tube has had all gases pumped out of it.
  • At each end of the tube is a metal piece called
    an electrode, which is connected through the
    glass to a metal terminal outside the tube.
  • These electrodes become electrically charged when
    they are connected to a high-voltage electrical
    source.

6
Atomic Structure Basic Concepts
Topic 2
Cathode-Ray Tube
  • When the electrodes are charged, rays travel in
    the tube from the negative electrode, which is
    the cathode, to the positive electrode, the
    anode.
  • Because these rays originate at the cathode, they
    are called cathode rays.

7
Atomic Structure Basic Concepts
Topic 2
Cathode-Ray Tube
  • Thomson found that the rays bent toward a
    positively charged plate and away from a
    negatively charged plate.
  • He knew that objects with like charges repel each
    other, and objects with unlike charges attract
    each other.

Click box to view movie clip.
8
Atomic Structure Basic Concepts
Topic 2
Cathode-Ray Tube
  • Thomson concluded that cathode rays are made up
    of invisible, negatively charged particles
    referred to as electrons.
  • These electrons had to come from the matter
    (atoms) of the negative electrode.

9
Atomic Structure Basic Concepts
Topic 2
Cathode-Ray Tube
  • From Thomsons experiments, scientists had to
    conclude that atoms were not just neutral
    spheres, but somehow were composed of
    electrically charged particles.
  • Reason should tell you that there must be a lot
    more to the atom than electrons.
  • Matter is not negatively charged, so atoms cant
    be negatively charged either.

10
Atomic Structure Basic Concepts
Topic 2
Cathode-Ray Tube
  • If atoms contained extremely light, negatively
    charged particles, then they must also contain
    positively charged particlesprobably with a much
    greater mass than electrons.

11
Atomic Structure Basic Concepts
Topic 2
Protons
  • In 1886, scientists discovered that a cathode-ray
    tube emitted rays not only from the cathode but
    also from the positively charged anode.
  • These rays travel in a direction opposite to that
    of cathode rays.

12
Atomic Structure Basic Concepts
Topic 2
Protons
  • Like cathode rays, they are deflected by
    electrical and magnetic fields, but in directions
    opposite to the way cathode rays are deflected.
  • Thomson was able to show that these rays had a
    positive electrical charge.
  • Years later, scientists determined that the rays
    were composed of positively charged subatomic
    particles called protons.

13
Atomic Structure Basic Concepts
Topic 2
Protons
  • At this point, it seemed that atoms were made up
    of equal numbers of electrons and protons.

14
Atomic Structure Basic Concepts
Topic 2
Rutherfords Gold Foil Experiment
  • In 1909, a team of scientists led by Ernest
    Rutherford in England carried out the first of
    several important experiments that revealed an
    arrangement far different from the cookie-dough
    model of the atom.

15
Atomic Structure Basic Concepts
Topic 2
Rutherfords Gold Foil Experiment
  • The experimenters set up a lead-shielded box
    containing radioactive polonium, which emitted a
    beam of positively charged subatomic particles
    through a small hole.

Click box to view movie clip.
16
Atomic Structure Basic Concepts
Topic 2
Rutherfords Gold Foil Experiment
  • Today, we know that the particles of the beam
    consisted of clusters containing two protons and
    two neutrons and are called alpha particles.
  • The sheet of gold foil was surrounded by a screen
    coated with zinc sulfide, which glows when struck
    by the positively charged particles of the beam.

17
Atomic Structure Basic Concepts
Topic 2
The Gold Foil Experiment
18
Atomic Structure Basic Concepts
Topic 2
The Nuclear Model of the Atom
  • To explain the results of the experiment,
    Rutherfords team proposed a new model of the
    atom.
  • Because most of the particles passed through the
    foil, they concluded that the atom is nearly all
    empty space.

Click box to view movie clip.
19
Atomic Structure Basic Concepts
Topic 2
The Nuclear Model of the Atom
  • Because so few particles were deflected, they
    proposed that the atom has a small, dense,
    positively charged central core, called a
    nucleus.

20
Atomic Structure Basic Concepts
Topic 2
The Nuclear Model of the Atom
  • The new model of the atom as pictured by
    Rutherfords group in 1911 is shown below.

21
Atomic Structure Basic Concepts
Topic 2
Atomic Numbers
  • The atomic number of an element is the number of
    protons in the nucleus of an atom of that
    element.
  • It is the number of protons that determines the
    identity of an element, as well as many of its
    chemical and physical properties.

22
Atomic Structure Basic Concepts
Topic 2
Atomic Numbers
  • Because atoms have no overall electrical charge,
    an atom must have as many electrons as there are
    protons in its nucleus.
  • Therefore, the atomic number of an element also
    tells the number of electrons in a neutral atom
    of that element.

23
Atomic Structure Basic Concepts
Topic 2
Masses
  • The mass of a neutron is almost the same as the
    mass of a proton.
  • The sum of the protons and neutrons in the
    nucleus is the mass number of that particular
    atom.

24
Atomic Structure Basic Concepts
Topic 2
Atomic Mass
  • In order to have a simpler way of comparing the
    masses of individual atoms, chemists have devised
    a different unit of mass called an atomic mass
    unit, which is given the symbol u.
  • An atom of the carbon-12 isotope contains six
    protons and six neutrons and has a mass number of
    12.

25
Atomic Structure Basic Concepts
Topic 2
Atomic Mass
  • Chemists have defined the carbon-12 atom as
    having a mass of 12 atomic mass units.
  • Therefore, 1 u 1/12 the mass of a carbon-12
    atom.
  • 1 u is approximately the mass of a single proton
    or neutron.

26
Atomic Structure Basic Concepts
Topic 2
Information in the Periodic Table
  • The number at the bottom of each box is the
    average atomic mass of that element.
  • This number is the weighted average mass of all
    the naturally occurring isotopes of that element.

27
Atomic Structure Basic Concepts
Topic 2
Electrons in Motion
  • Niels Bohr (1885-1962), a Danish scientist who
    worked with Rutherford, proposed that electrons
    must have enough energy to keep them in constant
    motion around the nucleus.
  • Electrons have energy of motion that enables them
    to overcome the attraction of the positive
    nucleus.

28
Atomic Structure Basic Concepts
Topic 2
Electrons in Motion
  • This energy keeps the electrons moving around the
    nucleus.
  • Bohrs view of the atom, which he proposed in
    1913, was called the planetary model.

29
Atomic Structure Basic Concepts
Topic 2
The Electromagnetic Spectrum
  • To boost a satellite into a higher orbit requires
    energy from a rocket motor.
  • One way to increase the energy of an electron is
    to supply energy in the form of high-voltage
    electricity.
  • Another way is to supply electromagnetic
    radiation, also called radiant energy.

30
Atomic Structure Basic Concepts
Topic 2
The Electromagnetic Spectrum
  • Radiant energy travels in the form of waves that
    have both electrical and magnetic properties.
  • These electromagnetic waves can travel through
    empty space, as you know from the fact that
    radiant energy from the sun travels to Earth
    every day.

31
Atomic Structure Basic Concepts
Topic 2
The Electromagnetic Spectrum
  • As you may already have guessed, electromagnetic
    waves travel through space at the speed of light,
    which is approximately 300 million meters per
    second.

32
Atomic Structure Basic Concepts
Topic 2
The Electromagnetic Spectrum
  • Electromagnetic radiation includes radio waves
    that carry broadcasts to your radio and TV,
    microwave radiation used to heat food in a
    microwave oven, radiant heat used to toast bread,
    and the most familiar form, visible light.
  • All of these forms of radiant energy are parts of
    a whole range of electromagnetic radiation called
    the electromagnetic spectrum.

33
Atomic Structure Basic Concepts
Topic 2
The Electromagnetic Spectrum
34
Atomic Structure Basic Concepts
Topic 2
Electrons and Light
  • The spectrum of light released from excited atoms
    of an element is called the emission spectrum of
    that element.

35
Atomic Structure Basic Concepts
Topic 2
Evidence for Energy Levels
  • Bohr theorized that electrons absorbed energy and
    moved to higher energy states.
  • Then, these excited electrons gave off that
    energy as light waves when they fell back to a
    lower energy state.

36
Atomic Structure Basic Concepts
Topic 2
Evidence for Energy Levels
  • Because electrons can have only certain amounts
    of energy, Bohr reasoned, they can move around
    the nucleus only at distances that correspond to
    those amounts of energy.
  • These regions of space in which electrons can
    move about the nucleus of an atom are called
    energy levels.

37
Atomic Structure Basic Concepts
Topic 2
The Electron Cloud Model
  • As a result of continuing research throughout the
    20th century, scientists today realize that
    energy levels are not neat, planetlike orbits
    around the nucleus of an atom.
  • Instead, they are spherical regions of space
    around the nucleus in which electrons are most
    likely to be found.

38
Atomic Structure Basic Concepts
Topic 2
The Electron Cloud Model
  • Electrons themselves take up little space but
    travel rapidly through the space surrounding the
    nucleus.
  • These spherical regions where electrons travel
    may be depicted as clouds around the nucleus.
  • The space around the nucleus of an atom where the
    atoms electrons are found is called the electron
    cloud.

39
Atomic Structure Basic Concepts
Topic 2
The Electron Cloud Model
40
Atomic Structure Basic Concepts
Topic 2
Electrons in Energy Level
  • How are electrons arranged in energy levels?
  • Each energy level can hold a limited number of
    electrons.
  • The lowest energy level is the smallest and the
    closest to the nucleus.

41
Atomic Structure Basic Concepts
Topic 2
Electrons in Energy Level
  • This first energy level holds a maximum of two
    electrons.
  • The second energy level is larger because it is
    farther away from the nucleus. It holds a maximum
    of eight electrons.
  • The third energy level is larger still and holds
    a maximum of 18 electrons.

42
Atomic Structure Basic Concepts
Topic 2
Energy Levels
  • A hydrogen atom has only one electron. Its in
    the first energy level.

43
Atomic Structure Basic Concepts
Topic 2
Electrons in Energy Level
  • The electrons in the outermost energy level are
    called valence electrons.
  • You can also use the periodic table as a tool to
    predict the number of valence electrons in any
    atom in Groups 1, 2, 13, 14, 15, 16, 17, and 18.
  • All atoms in Group 1, like hydrogen, have one
    valence electron. Likewise, atoms in Group 2 have
    two valence electrons.

44
Atomic Structure Basic Concepts
Topic 2
Electrons in Energy Level
  • An oxygen atom has eight electrons. Two of these
    fill the first energy level, and the remaining
    six are in the second energy level.

45
Atomic Structure Basic Concepts
Topic 2
Lewis Dot Diagrams
  • Because valence electrons are so important to the
    behavior of an atom, it is useful to represent
    them with symbols.

46
Atomic Structure Basic Concepts
Topic 2
Lewis Dot Diagrams
  • A Lewis dot diagram illustrates valence electrons
    as dots (or other small symbols) around the
    chemical symbol of an element.

47
Atomic Structure Basic Concepts
Topic 2
Lewis Dot Diagrams
  • Each dot represents one valence electron.
  • In the dot diagram, the elements symbol
    represents the core of the atomthe nucleus plus
    all the inner electrons.

48
Basic Concept Questions
Topic 2
Question 1
How does the atomic number of an element differ
from the elements mass number?
Answer
The atomic number of an element is the number of
protons in the nucleus. The mass number is the
sum of the number of protons and neutrons.
49
Basic Concept Questions
Topic 2
Question 2
Write a Lewis dot diagram for each of the
following.
A. Chlorine
B. Calcium
C. Potassium
50
Basic Concept Questions
Topic 2
Answer
A. Chlorine
B. Calcium
C. Potassium
51
Basic Concept Questions
Topic 2
Question 3
Give an example for each type of electromagnetic
energy listed below.
A. Ultraviolet light
B. Infrared light
C. Visible light
52
Basic Concept Questions
Topic 2
Answer
Sample answers
A. ultraviolet light
part of sunlight
radiant heat
B. infrared light
the spectrum of light we see as color
C. visible light
53
Atomic Structure Additional Concepts
Topic 2
Additional Concepts
54
Atomic Structure Additional Concepts
Topic 2
Energy Levels and Sublevels
  • The emission spectrum for each element has a
    characteristic set of spectral lines.
  • This means that the energy levels within the atom
    must also be characteristic of each element.
  • But when scientists investigated multi-electron
    atoms, they found that their spectra were far
    more complex than would be anticipated by the
    simple set of energy levels predicted for
    hydrogen.

55
Atomic Structure Additional Concepts
Topic 2
Energy Levels and Sublevels
  • Notice that these spectra have many more lines
    than the spectrum of hydrogen.

56
Atomic Structure Additional Concepts
Topic 2
Energy Levels and Sublevels
  • Some lines are grouped close together, and there
    are big gaps between these groups of lines.

57
Atomic Structure Additional Concepts
Topic 2
Energy Levels and Sublevels
  • The big gaps correspond to the energy released
    when an electron jumps from one energy level to
    another.

58
Atomic Structure Additional Concepts
Topic 2
Energy Levels and Sublevels
  • The interpretation of the closely spaced lines is
    that they represent the movement of electrons
    from levels that are not very different in
    energy.
  • This suggests that sublevelsdivisions within a
    levelexist within a given energy level.

59
Atomic Structure Additional Concepts
Topic 2
Energy Levels and Sublevels
  • If electrons are distributed over one or more
    sublevels within an energy level, then these
    electrons would have only slightly different
    energies.
  • The energy sublevels are designated as s, p, d,
    or f.

60
Atomic Structure Additional Concepts
Topic 2
Energy Levels and Sublevels
  • Each energy level has a specific number of
    sublevels, which is the same as the number of the
    energy level.
  • For example, the first energy level has one
    sublevel. Its called the 1s sublevel.
  • The second energy level has two sublevels, the 2s
    and 2p sublevels

61
Atomic Structure Additional Concepts
Topic 2
Energy Levels and Sublevels
  • The third energy level has three sublevels the
    3s, 3p, and 3d sublevels and the fourth energy
    level has four sublevels the 4s, 4p, 4d, and 4f
    sublevels.
  • Within a given energy level, the energies of the
    sublevels, from lowest to highest, are s, p, d,
    and f.

62
Atomic Structure Additional Concepts
Topic 2
The Distribution of Electrons in Energy Levels
  • A specific number of electrons can go into each
    sublevel.

63
Atomic Structure Additional Concepts
Topic 2
The Distribution of Electrons in Energy Levels
  • An s sublevel can have a maximum of two
    electrons, a p sublevel can have six electrons,

64
Atomic Structure Additional Concepts
Topic 2
The Distribution of Electrons in Energy Levels
  • a d sublevel can have ten electrons, and an f
    sublevel can have 14 electrons.

65
Atomic Structure Additional Concepts
Topic 2
Orbitals
  • In the 1920s, Werner Heisenberg reached the
    conclusion that its impossible to measure
    accurately both the position and energy of an
    electron at the same time.
  • This principle is known as the Heisenberg
    uncertainty principle. In 1932, Heisenberg was
    awarded the Nobel Prize in Physics for this
    discovery, which led to the development of the
    electron cloud model to describe electrons in
    atoms.

66
Atomic Structure Additional Concepts
Topic 2
Orbitals
  • The electron cloud model is based on the
    probability of finding an electron in a certain
    region of space at any given instant.
  • In any atom, electrons are distributed into
    sublevels and orbitals in the way that creates
    the most stable arrangement that is, the one
    with lowest energy.

67
Atomic Structure Additional Concepts
Topic 2
Electron Configurations
  • This most stable arrangement of electrons in
    sublevels and orbitals is called an electron
    configuration.
  • Electrons fill orbitals and sublevels in an
    orderly fashion beginning with the innermost
    sublevels and continuing to the outermost.

68
Atomic Structure Additional Concepts
Topic 2
Building Electron Configurations
  • The electron configuration for carbon is
    1s22s22p2.

69
Atomic Structure Additional Concepts
Topic 2
Building Electron Configurations
70
Atomic Structure Additional Concepts
Topic 2
Building Electron Configurations
  • At element number 10, neon, the p sublevel is
    filled with six electrons.
  • The electron configuration for neon is 1s22s22p6.
  • Neon has eight valence electrons two are in an s
    orbital and six are in p orbitals.

71
Atomic Structure Additional Concepts
Topic 2
Noble Gases
  • Each period ends with a noble gas, so all the
    noble gases have filled energy levels and,
    therefore, stable electron configurations.

72
Atomic Structure Additional Concepts
Topic 2
Noble Gases
73
Atomic Structure Additional Concepts
Topic 2
Calculating Atomic Mass
74
Atomic Structure Additional Concepts
Topic 2
Calculating Atomic Mass
  • Copper exists as a mixture of two isotopes.
  • The lighter isotope (Cu-63), with 29 protons and
    34 neutrons, makes up 69.17 of copper atoms.
  • The heavier isotope (Cu-65), with 29 protons and
    36 neutrons, constitutes the remaining 30.83 of
    copper atoms.

75
Atomic Structure Additional Concepts
Topic 2
Calculating Atomic Mass
  • The atomic mass of Cu-63 is 62.930 amu, and the
    atomic mass of Cu-65 is 64.928 amu.
  • Use the data above to compute the atomic mass of
    copper.

76
Atomic Structure Additional Concepts
Topic 2
Calculating Atomic Mass
  • First, calculate the contribution of each isotope
    to the average atomic mass, being sure to convert
    each percent to a fractional abundance.

77
Atomic Structure Additional Concepts
Topic 2
Calculating Atomic Mass
  • The average atomic mass of the element is the sum
    of the mass contributions of each isotope.

78
Additional Assessment Questions
Topic 2
Question 1
Write electron configurations and abbreviated
electron configurations of the following elements.
A. Boron
B. Fluorine
C. Phosphorus
79
Additional Assessment Questions
Topic 2
Answer
A. Boron
B. Fluorine
C. Phosphorus
80
Additional Assessment Questions
Topic 2
Question 2
The table on the next slide shows the five
isotopes of germanium found in nature, the
abundance of each isotope, and the atomic mass of
each isotope.
81
Additional Assessment Questions
Topic 2
Calculate the atomic mass of germanium.
82
Additional Assessment Questions
Topic 2
Answer
72.59 amu
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