Title: John Dalton 17661844, an English schoolteacher and chemist, studied the results of experiments by ma
1Atomic 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.
2Atomic 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.
3Atomic 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.
4Atomic Structure Basic Concepts
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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.
5Atomic Structure Basic Concepts
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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.
6Atomic Structure Basic Concepts
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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.
7Atomic Structure Basic Concepts
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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.
8Atomic Structure Basic Concepts
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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.
9Atomic 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.
10Atomic Structure Basic Concepts
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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.
11Atomic Structure Basic Concepts
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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.
12Atomic Structure Basic Concepts
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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.
13Atomic Structure Basic Concepts
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Protons
- At this point, it seemed that atoms were made up
of equal numbers of electrons and protons.
14Atomic Structure Basic Concepts
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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.
15Atomic Structure Basic Concepts
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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.
16Atomic 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.
17Atomic Structure Basic Concepts
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The Gold Foil Experiment
18Atomic Structure Basic Concepts
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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.
19Atomic Structure Basic Concepts
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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.
20Atomic Structure Basic Concepts
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The Nuclear Model of the Atom
- The new model of the atom as pictured by
Rutherfords group in 1911 is shown below.
21Atomic Structure Basic Concepts
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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.
22Atomic Structure Basic Concepts
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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.
23Atomic 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.
24Atomic Structure Basic Concepts
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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.
25Atomic Structure Basic Concepts
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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.
26Atomic Structure Basic Concepts
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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.
27Atomic Structure Basic Concepts
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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.
28Atomic Structure Basic Concepts
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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.
29Atomic Structure Basic Concepts
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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.
30Atomic Structure Basic Concepts
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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.
31Atomic Structure Basic Concepts
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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.
32Atomic Structure Basic Concepts
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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.
33Atomic Structure Basic Concepts
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The Electromagnetic Spectrum
34Atomic Structure Basic Concepts
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Electrons and Light
- The spectrum of light released from excited atoms
of an element is called the emission spectrum of
that element.
35Atomic Structure Basic Concepts
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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.
36Atomic Structure Basic Concepts
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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.
37Atomic Structure Basic Concepts
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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.
38Atomic 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.
39Atomic Structure Basic Concepts
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The Electron Cloud Model
40Atomic Structure Basic Concepts
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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.
41Atomic Structure Basic Concepts
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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.
42Atomic Structure Basic Concepts
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Energy Levels
- A hydrogen atom has only one electron. Its in
the first energy level.
43Atomic Structure Basic Concepts
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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.
44Atomic Structure Basic Concepts
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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.
45Atomic Structure Basic Concepts
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Lewis Dot Diagrams
- Because valence electrons are so important to the
behavior of an atom, it is useful to represent
them with symbols.
46Atomic Structure Basic Concepts
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Lewis Dot Diagrams
- A Lewis dot diagram illustrates valence electrons
as dots (or other small symbols) around the
chemical symbol of an element.
47Atomic Structure Basic Concepts
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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.
48Basic 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.
49Basic Concept Questions
Topic 2
Question 2
Write a Lewis dot diagram for each of the
following.
A. Chlorine
B. Calcium
C. Potassium
50Basic Concept Questions
Topic 2
Answer
A. Chlorine
B. Calcium
C. Potassium
51Basic 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
52Basic 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
53Atomic Structure Additional Concepts
Topic 2
Additional Concepts
54Atomic Structure Additional Concepts
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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.
55Atomic Structure Additional Concepts
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Energy Levels and Sublevels
- Notice that these spectra have many more lines
than the spectrum of hydrogen.
56Atomic Structure Additional Concepts
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Energy Levels and Sublevels
- Some lines are grouped close together, and there
are big gaps between these groups of lines.
57Atomic Structure Additional Concepts
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Energy Levels and Sublevels
- The big gaps correspond to the energy released
when an electron jumps from one energy level to
another.
58Atomic Structure Additional Concepts
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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.
59Atomic 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.
60Atomic 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
61Atomic 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.
62Atomic Structure Additional Concepts
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The Distribution of Electrons in Energy Levels
- A specific number of electrons can go into each
sublevel.
63Atomic Structure Additional Concepts
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The Distribution of Electrons in Energy Levels
- An s sublevel can have a maximum of two
electrons, a p sublevel can have six electrons,
64Atomic Structure Additional Concepts
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The Distribution of Electrons in Energy Levels
- a d sublevel can have ten electrons, and an f
sublevel can have 14 electrons.
65Atomic Structure Additional Concepts
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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.
66Atomic Structure Additional Concepts
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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.
67Atomic Structure Additional Concepts
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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.
68Atomic Structure Additional Concepts
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Building Electron Configurations
- The electron configuration for carbon is
1s22s22p2.
69Atomic Structure Additional Concepts
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Building Electron Configurations
70Atomic Structure Additional Concepts
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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.
71Atomic Structure Additional Concepts
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Noble Gases
- Each period ends with a noble gas, so all the
noble gases have filled energy levels and,
therefore, stable electron configurations.
72Atomic Structure Additional Concepts
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Noble Gases
73Atomic Structure Additional Concepts
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Calculating Atomic Mass
74Atomic Structure Additional Concepts
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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.
75Atomic Structure Additional Concepts
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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.
76Atomic 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.
77Atomic Structure Additional Concepts
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Calculating Atomic Mass
- The average atomic mass of the element is the sum
of the mass contributions of each isotope.
78Additional Assessment Questions
Topic 2
Question 1
Write electron configurations and abbreviated
electron configurations of the following elements.
A. Boron
B. Fluorine
C. Phosphorus
79Additional Assessment Questions
Topic 2
Answer
A. Boron
B. Fluorine
C. Phosphorus
80Additional 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.
81Additional Assessment Questions
Topic 2
Calculate the atomic mass of germanium.
82Additional Assessment Questions
Topic 2
Answer
72.59 amu