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

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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.

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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.

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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.
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Atomic 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.

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Atomic 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.

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Atomic 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.

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Atomic 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.
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Atomic 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.

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Atomic Structure Basic Concepts
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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.

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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.

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Atomic 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.

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Atomic 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.

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Atomic 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.

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Atomic 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.

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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.
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Atomic Structure Basic Concepts
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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.

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Atomic Structure Basic Concepts
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The Gold Foil Experiment
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Atomic 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.
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Atomic 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.

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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.

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Atomic 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.

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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.

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Atomic Structure Basic Concepts
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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.

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Atomic 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.

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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.

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Atomic 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.

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Atomic 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.

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Atomic 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.

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Atomic 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.

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Atomic 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.

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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.

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Atomic 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.

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Atomic Structure Basic Concepts
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The Electromagnetic Spectrum
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Atomic 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.

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Atomic 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.

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Atomic 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.

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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.

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Atomic Structure Basic Concepts
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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.

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Atomic Structure Basic Concepts
Topic 2
The Electron Cloud Model
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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.

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Atomic 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.

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Atomic Structure Basic Concepts
Topic 2
Energy Levels

• A hydrogen atom has only one electron. Its in
  the first energy level.

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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.

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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.

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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.

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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.

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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.

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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.
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Basic Concept Questions
Topic 2
Question 2
Write a Lewis dot diagram for each of the
following.
A. Chlorine
B. Calcium
C. Potassium
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Basic Concept Questions
Topic 2
Answer
A. Chlorine
B. Calcium
C. Potassium
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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
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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
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Atomic Structure Additional Concepts
Topic 2
Additional Concepts
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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.

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Atomic Structure Additional Concepts
Topic 2
Energy Levels and Sublevels

• Notice that these spectra have many more lines
  than the spectrum of hydrogen.

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Atomic 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.

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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.

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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.

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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.

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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

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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.

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Atomic Structure Additional Concepts
Topic 2
The Distribution of Electrons in Energy Levels

• A specific number of electrons can go into each
  sublevel.

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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,

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Atomic 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.

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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.

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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.

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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.

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Atomic Structure Additional Concepts
Topic 2
Building Electron Configurations

• The electron configuration for carbon is
  1s22s22p2.

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Atomic Structure Additional Concepts
Topic 2
Building Electron Configurations
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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.

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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.

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Atomic Structure Additional Concepts
Topic 2
Noble Gases
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Atomic Structure Additional Concepts
Topic 2
Calculating Atomic Mass
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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.

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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.

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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.

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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.

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Additional Assessment Questions
Topic 2
Question 1
Write electron configurations and abbreviated
electron configurations of the following elements.
A. Boron
B. Fluorine
C. Phosphorus
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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.
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Additional Assessment Questions
Topic 2
Calculate the atomic mass of germanium.
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Additional Assessment Questions
Topic 2
Answer
72.59 amu