1. Quantum Theory
and the Atom
ELECTRONS IN ATOMS AND THE PERIODIC TABLE
PREPARED BY: TYPE YOUR NAME HERE
2. LEARNING OBJECTIVE
Explain how the Quantum
Mechanical Model of the atom
describes the energies and
positions of the electrons
3. Learning Goals
Compare the Bohr and quantum mechanical
models of the atom.
Explain the impact of de Broglie’s wave particle
duality and the Heisenberg uncertainty principle on
the current view of electrons in atoms.
Identify the relationships among a hydrogen
atom’s energy levels, sublevels, and atomic
orbitals.
4. Bohr’s Model of the Atom
Einstein’s theory of light’s dual nature
accounted for several unexplainable
phenomena, but it did not explain why
atomic emission spectra of elements
were discontinuous.
5. Bohr’s Model of the Atom
In 1913, Niels Bohr, a Danish
physicist working in Rutherford’s
laboratory, proposed a quantum
model for the hydrogen atom that
seemed to answer this question.
6.
7. Bohr’s Model of the
Atom
The lowest allowable energy state of
an atom is called its ground state.
When an atom gains energy, it is in an
excited state.
8. Bohr’s Model of the Atom
Bohr suggested that an electron moves around the
nucleus only in certain allowed circular orbits.
9. Bohr’s Model of the Atom
Each orbit was given a
number, called the quantum
number.
Bohr orbits are like steps of a
ladder, each at a specific
distance from the nucleus and
each at a specific energy.
10. Bohr’s Model of the Atom
Hydrogen’s single electron is in the n =
1 orbit when it is in the ground state.
When energy is added, the electron moves
to the n = 2 orbit.
11. Bohr’s Model of the Atom
The electron releases energy as it falls
back towards the ground state.
12. Bohr’s Model of the Atom
Bohr’s model explained the hydrogen’s
spectral lines, but failed to explain any other
element’s lines.
For this and other reasons, the Bohr model
was replaced with a more sophisticated model
called the quantum-mechanical or wave-
mechanical model.
13. Quantum Mechanical
Model
Louis de Broglie (1892–1987) hypothesized
that particles, including electrons, could also
have wavelike behaviors.
Electrons do not behave like particles flying
through space.
We cannot, in general, describe their exact paths.
14. Quantum Mechanical
Model
Heisenberg showed it is impossible to take any
measurement of an object without disturbing it.
The Heisenberg uncertainty principle states
that it is fundamentally impossible to know
precisely both the velocity and position of a
particle at the same time.
15.
16. Quantum Mechanical
Model
The only quantity that can be
known is the probability for an
electron to occupy a certain
region around the nucleus.
17. Quantum Mechanical
Model
Schrödinger treated electrons as waves in a
model called the quantum mechanical
model of the atom.
Schrödinger’s equation applied equally well to
elements other than hydrogen (unlike Bohr’s
model).
18. Quantum Mechanical
Model
Orbitals are different from
orbits in that they represent
probability maps that show a
statistical distribution of where
the electron is likely to be
found.
19. Quantum Mechanical
Model
In the quantum-mechanical model, a
number and a letter specify an orbital.
The lowest-energy orbital is called
the 1s orbital.
It is specified by the number 1
and the letter s.
20. Hydrogen’s Atomic Orbitals
The number is called the Principal
quantum number (n) and it
indicates the relative size and
energy of atomic orbitals.
n specifies the atom’s major energy
levels, called the principal energy
levels.
28. Hydrogen’s Atomic Orbitals
Orbitals are sometimes represented by dots, where the
dot density is proportional to the probability of finding
the electron.
The dot density for the 1s orbital is greatest near the
nucleus and decreases farther away from the nucleus.
The electron is more likely to be found close to the
nucleus than far away from it.
31. Hydrogen’s Atomic Orbitals
At any given time, hydrogen’s electron
can occupy just one orbital.
When hydrogen is in the ground state, the
electron occupies the 1s orbital.
When the atom gains a quantum of energy,
the electron is excited to one of the
unoccupied orbitals.
32. Quantum Numbers
A set of quantum numbers gives an
information about the atomic orbital where an
electrons may be found
A. principal
B. Azimuthal
C. Magnetic
D. Spin
33. A. Principal quantum number (n)
- indicates the energy level
n= 1,2,3,4 ….
B. Azimutham Quantum Number (ℓ)
- specifies the sublevel or subshell
ℓ= 0 to n-1
34. c. Magnetic quantum number (mℓ)
- indicates the specific orbital within the sublevel where
the electron is found
-ℓ to +ℓ
Example: n=1, ℓ = 0 , mℓ = 0
n =2, ℓ = 0,1 , mℓ = 0, -1, 0,
+1
35. D. Spin quantum Number
- according to Pauli Exclusion
Principle, only a maximum of two
electrons can occupy an orbital, and
they must have opposite spins to
minimize repulsion between them.
+ ½ or - ½
37. 1.What are the possible sets of
quantum numbers that can describe a
2p electron in an atom?
2. Give the set of quantum numbers
for each of the six electrons that
occupy the 4p orbitals
38. 3.Give the electron configuration of Li.
Give the set of quantum numbers that
describe the outermost electron in
lithium as shown in the orbital diagram
below.
4. Give the set of quantum numbers
of Cr
39. Determine the element whose outermost valence electron
is represented by the following quantum numbers.
a. n=1, l= 0, ml= 0, ms=-1/2
b. n=2, l=1, ml= 0, ms= +1/2
c. n=3, l=1, ml= 0, ms= +1/2
d. n=4, l=2, ml= 0, ms= +1/2
e. n= 6, l=0, ml= 0, ms= -1/2
40. Which of the following are
permissible sets of quantum
numbers?
n = 4, l = 4, ml = 0, ms = ½
n = 3, l = 2, ml = 1, ms = -½
n = 2, l = 0, ml = 0, ms = ³/²
n = 5, l = 3, ml = -3, ms = ½
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