Download Chapter 13 Electrons in Atoms

Chapter 13 Electrons in
Atoms
C. Smith
I. Models of the Atom
A. The Evolution of Atomic Models
•
•
1. There are four major models of the atom
that have been developed from John Dalton
theory.
2. Dalton Atomic Theory
a. He theorized that an atom was
indivisible, uniformly dense sphere.
b. He theorized that all atoms of the same
element have the same mass and the same
chemical behaviors.
c. He theorized that atoms of different
elements have different chemical behaviors.
d. He theorized that atoms of different
elements combine to form compounds. (Example
— H2O)
I. Models of the Atom
A. The Evolution of Atomic Models
•
3. J.J. Thomson realized that the accepted
model did not take electrons into account.
a. He is credited with the discovery of the
negatively charged particles called electrons.
b. He theorized that the atom is a dense
sphere with a positive charge and also contains
negative charged particles.
c. His model is also known as the Plum
Pudding model.
I. Models of the Atom
A. The Evolution of Atomic Models
•
4. Ernest Rutherford expanded on
Thomson’s theory.
a. The atom has a very dense center
of positive charge called the nucleus.
b. The nucleus contains the protons
for the atom and make up more than
99.9% of its mass.
c. The electrons surround the
nucleus.
I. Models of the Atom
A. The Evolution of Atomic Models
•
5. Niels Bohr proposed a model in which the
electrons move around the nucleus.
a. He theorized that the electron orbits the
nucleus.
b. He theorized that the orbits were different
energy levels that the electrons travel in and can be
excited to a high energy level.
c. He theorized that the electrons did not lose
energy and fall into the nucleus. (The weakness in
Rutherford’s theory.)
I. Models of the Atom
A. The Evolution of Atomic Models
•
6. A quantum of energy is the
amount of energy required to move an
electron from its present energy level
to the next higher one. (Also called a
quantum leap)
I. Models of the Atom
B. The Quantum Mechanical Model
•
1. Erwin Schrödinger related the
amplitude of the electron wave, Y
(psi), to any point in space around
the nucleus.
2. His equation treated the electron
as a wave and developed an equation
to describe this behavior.
I. Models of the Atom
B. The Quantum Mechanical Model
•
3. The quantum mechanical model comes from
the mathematical solutions to Schrödinger
equation.
4. The quantum mechanical model does not
define an exact path for the electron to take
around the nucleus but instead estimates a
probability of finding the electron in a certain
position.
5. Since the volume occupied by an electron is
somewhat vague, it is better to refer to an
electron cloud.
I. Models of the Atom
B. The Quantum Mechanical Model
I. Models of the Atom
C. Atomic Orbitals
•
1. Electrons can occupy only specific
energy levels.
2. These energy levels, referred to
as “n” is called the principal quantum
number.
3. The maximum number of electrons
that a level can contain is 2n2
(Whole number integers only).
I. Models of the Atom
C. Atomic Orbitals
•
4. These are referred to as sublevels
and the number of sublevels for each
energy level is equal to the value of
the principal quantum number.
5. The lowest energy level is “s”.
6. The second lowest is “p” ,the third
lowest level is “d”, and the remain
level is “f”.
I. Models of the Atom
C. Atomic Orbitals
•
7. The “s” orbital is spherical in shape and
contains 2 electrons and is also called the
ground state.
8. The “p” level is barbell shape and exist
along the axis of the plane.
9. The “d” orbitals exist in the plane.
10. The “s” level contains 1 pair of
electrons, “p” contains 3 pairs, “d“
contains 5 pairs, and “f” contains 7 pairs.
II. Electron Arrangement in Atoms
A. Electron Configurations
•
1. The ways in which electrons are
arranged around the nucleus is called
electron configuration.
2. The are three rule that tell you
how to find the configurations.
a. Aufbau principle
b. Pauli Exclusion principle
c. Hund’s Rule
II. Electron Arrangement in Atoms
A. Electron Configurations
•
2a This is called the Aufbau
principle.
1. Electrons enter at the lowest
energy level.
2. Some energy levels overlap
into the adjacent principal energy
level.
II. Electron Arrangement in Atoms
A. Electron Configurations
II. Electron Arrangement in Atoms
A. Electron Configurations
•
2b. This is called the Pauli exclusion
principle.
1. Spectral data shows that only 2
electrons can exist in the same orbital.
2. Electrons behave as if they were
spinning about their own axis.
3. When electrons occupy the same
orbital – they are said to spin in opposite
directions (assign +1/2 and – 1/2).
II. Electron Arrangement in Atoms
A. Electron Configurations
•
2c. This is called Hund’s Rule.
1. Also with the principle, you
must have all orbital filled with one
electron before you can add the
other electron with opposite spin to
the orbital.
2 . All elements would like to have
a completely filled orbital and the
maximum number of electrons that
can exist in a filled orbital is eight.
II. Electron Arrangement in Atoms
A. Electron Configurations
•
3. When writing electron configurations,
you must know the total number of
electrons for the element (atomic
number).
4. Write down the sequence of orbitals.
5. Draw circle to represent the orbitals.
6. Place arrows (or slashes) to represent
the electrons.
II. Electron Arrangement in Atoms
A. Electron Configurations
II. Electron Arrangement in Atoms
A. Electron Configurations
II. Electron Arrangement in Atoms
B. Exceptional Electron Configurations
•
1. Filled sublevels are more stable
than partial filled or half-filled
sublevels.
2. But sometimes half-filled may be
more stable than other
configurations.
III. Physic and the Quantum Mechanical
Model
A. Light and Atomic Spectra
•
1. This energy consist of variation in
electric and magnetic fields taking
place in a regular, repeating fashion.
(Electromagnetic energy)
2. Light is a form of electromagnetic
radiation
III. Physic and the Quantum
Mechanical Model
A. Light and Atomic Spectra
•
3. If you plot the strength of the
variation against time, the graph
shows “waves” of energy.
4. The number of waves peaks
that occur in a unit of time is
called the frequency of the wave
(Greek letter v and units are
Hertz (Hz)).
III. Physic and the Quantum
Mechanical Model
A. Light and Atomic Spectra
•
5. The distance between the peaks
is the wavelength (Greek letter λ)
and the amplitude of a wave is the
height from the maximum
displacement from zero.
6. These characteristics of waves
are related by the statement c= λv
where c is the speed of light which
is 3.0 x 10 8 m/s.
III. Physic and the Quantum
Mechanical Model
A. Light and Atomic Spectra
•
7. The wavelengths of light can
separate into a spectrum of colors.
8. This is part of the visible
spectrum.
9. There are two types of
spectrums.
a. Adsorption spectrum.
b. Emission spectrum.
III. Physic and the Quantum
Mechanical Model
A. Light and Atomic Spectra
•
10. Adsorption spectrum is when
the energy gained by the excited
electron is is absorbed so that it is
missing in visible spectrum.
11. Emission spectrum is when the
excited electrons lose the energy
and it is emitted at specific points
on the visible spectrum that appear
as single lines on a detector.
III. Physic and the Quantum
Mechanical Model
B. The Quantum Concept and
the Photoelectric Effect
•
1. Max Planck used Bohr’s theory
to develop his hypothesis.
2. He assumed that energy is given
off in packets called quanta or
photons instead of a steady
stream.
III. Physic and the Quantum
Mechanical Model
B. The Quantum Concept and the
Photoelectric Effect
•
3. He stated that the amount of
energy given off is related to the
frequency of light (v - Greek
letter nu).
4. He thought a quantum energy
was equal to E = hv where h is the
constant 6.63 x 10 -34 J/Hz (Hz =
Hertz).
III. Physic and the Quantum
Mechanical Model
B. The Quantum Concept and
the Photoelectric Effect
•
5. Albert Einstein proposed that
light could be described as a quanta
of energy that behaved as if they
were particles.
6. The dual wave-particle behavior
is called the photoelectric effect.
III. Physic and the Quantum
Mechanical Model
B. The Quantum Concept and
the Photoelectric Effect
•
7. In the photoelectric effect,
metals eject electrons when light
shines on them.
8. The frequency and the
wavelength of the light determine if
the photoelectric effect will occur.
III. Physic and the Quantum
Mechanical Model
C. An Explanation of
Atomic Spectra
•
1. Consider the electron of a
hydrogen atom in its lowest energy
level, or ground state.
2. The quantum numbers represent
the different energy states.
III. Physic and the Quantum
Mechanical Model
C. An Explanation of
Atomic Spectra
•
3. The difference between these
energy states corresponds to the
lines in the hydrogen spectrum.
4. With more complex atoms more
than one electron is present and
the interaction between electrons
make solution to the equation
impossible because electrons have
the same charge.
III. Physic and the Quantum
Mechanical Model
C. An Explanation of Atomic
Spectra
•
5. It is possible to approximate the
electronic structure of a multi-electron
atom.
6. This approximation is made by first
calculating the various energy states
and quantum numbers.
7. It is assumed that the various
electrons in multi-electron atom occupy
the same energy states without affecting
each other.
III. Physic and the Quantum
Mechanical Model
D. Quantum Mechanic
•
1. Louis De Broglie proposed an idea
based on Planck’s theory and
Einstein’s relationship of matter and
energy.
2. Using the two formulas, he
equated mc2 = hν (v = frequency).
III. Physic and the Quantum
Mechanical Model
D. Quantum Mechanic
•
3. He substituted v * for the
velocity of light (c) so that mv *2 =
hv and v /λ for v to get mv *2 =
hv /λ. (λ - Lamda = wavelength)
4. To determine wavelength (λ),
the equation becomes λ = h/mv .
III. Physic and the Quantum
Mechanical Model
D. Quantum Mechanic
•
5. This allows for predictions of
the wavelength of a particles.
6. Werner Heisenburg refined
ideas about atomic structure.
7. He stated that it is impossible
to know the exact position and
momentum of an electron in an
atom.
III. Physic and the Quantum
Mechanical Model
D. Quantum Mechanic
•
8. Using the equation for momentum, he
proposed that mv = p where m is mass
and p is momentum.
9. The uncertainty of position and
momentum are related to Planck’s
constant ∆p ∆x > h where p is
momentum and x is position (∆ =
change).
10. Because h is constant, ∆ p and ∆ x
are inversely proportional to each other.