First Year in Dentistry First Semester Al-Azhar University - Gaza Lama El Banna general chemistry

1. Chapter 6
Electronic Structure of Atoms

2. Electronic Structure
• The Wave Nature of Light
Wavelength and amplitude.
Wavelength (l) is the distance between
identical points on successive waves.
Amplitude: is the vertical distance from the
midline of a wave to the peak or trough.

3. Two waves having
different wavelengths
and frequencies. The
wavelength of the top
wave is three times that
of the lower wave, but its
frequency is only one-
third that of the lower
wave. Both waves have
the same
speed and amplitude.
frequency (n) is the number of waves that pass through a particular
point in 1 second (Hz = 1 cycle/s).
• The Wave Nature of Light

4. Types of electromagnetic radiation. Gamma rays have the shortest wavelength
and highest frequency; radio waves have the longest wavelength and the lowest
frequency. Each type of radiation is spread over a specifi c range of wavelengths
(and frequencies)

5. Visible light ranges from a wavelength of 400 nm (violet) to 700 nm (red).
All electromagnetic radiation
.= c

6. Mystery #1, “Black Body Problem”
Solved by Planck in 1900
Energy (light) is emitted or absorbed in discrete units
(quantum).
•Planck gave the name quantum to the smallest
quantity of energy that can be emitted (or absorbed) in
the form of electromagnetic radiation. The energy E
of a single quantum of energy is given by
E = h
h is called Planck’s constant = 6.63 x 10-34 J.s
E = hc/
7.1

7. Light has both:
1. wave nature
2. particle nature
Mystery #2, “Photoelectric Effect”
Solved by Einstein in 1905
Class practice :
Calculate the energy (in joules) of
A. a photon with a wavelength of 5.00 3 10 4 nm (infrared region) and
B. a photon with a wavelength of 5.00 X 10-22 nm (X ray region).
Solution
A. 3.98 X 10-21 J
B. 3.98 X 10-15 J
Because the energy of a photon increases with decreasing
wavelength, we see that an “X-ray” photon is 1 3 10 6 , or a million
times, more energetic than an “infrared” photon.

8. 1. e- can have only specific (quantized)
energy values
2. light is emitted as e- moves from one
energy level to a lower energy level
Bohr’s Model of
the Atom (1913)
En = -RH ( )
1
n2
n (principal quantum number) = 1,2,3,…
RH (Rydberg constant) = 2.18 x 10-18J
7.3

9. Ephoton = DE = Ef - Ei
Ef = -RH ( )
1
n2
f
Ei = -RH ( )
1
n2
i
i f
DE = RH ( )
1
n2
1
n2
7.3
RH is the Rydberg constant
n is the principal quantum number
En = -RH ( )
1
n2
Bohr showed the energy a H
atom can have is equal to:

10. • Knowing that light has a particle nature, it seems
reasonable to ask if matter has a wave nature.
• Using Einstein’s and Planck’s equations, de Broglie
showed:
• The momentum, mv, is a particle property, whereas  is a
wave property.
• de Broglie summarized the concepts of waves and
particles, with noticeable effects if the objects are small.
The Wave Behavior of Matter


m
h


11. The Uncertainty Principle
• Heisenberg’s Uncertainty Principle: on the mass scale
of atomic particles, we cannot determine exactly the
position, direction of motion, and speed simultaneously.
• For electrons: we cannot determine their momentum and
position simultaneously.
• If Dx is the uncertainty in position and Dmv is the
uncertainty in momentum, then
The Wave Behavior of Matter


4
h
mx DD

12. • Schrödinger proposed an equation that contains both
wave and particle terms.
• Solving the equation leads to wave functions.
• The wave function gives the shape of the electronic
orbital.
• The square of the wave function, gives the probability of
finding the electron,
• that is, gives the electron density for the atom.
Quantum Mechanics and Atomic Orbitals

13. Electron Density Distribution
Probability of finding an electron in a hydrogen atom in its ground
state.

14. 1. Schrödinger’s equation requires 3 quantum numbers:
2. Principal Quantum Number, n. This is the same as Bohr’s n. As n
becomes larger, the atom becomes larger and the electron is further
from the nucleus. (n = 1, 2, 3…)
2. Azimuthal Quantum Number, l. This quantum number depends on
the value of n. The values of l begin at 0 and increase to (n - 1). We
usually use letters for l (s, p, d and f for l = 0, 1, 2, and 3). Usually we
refer to the s, p, d and f-orbitals. (l = 0, 1, 2…n-1). Defines the shape
of the orbitals.
3. Magnetic Quantum Number, ml. This quantum number depends on
l. The magnetic quantum number has integral values between -l and
+l. Magnetic quantum numbers give the 3D orientation of each
orbital in space. (m = -l…0…+1)
The Three Quantum Numbers

15. Orbitals and Quantum Numbers

16. • All s-orbitals are spherical.
• As n increases, the s-orbitals get larger.
• As n increases, the number of nodes increase.
• A node is a region in space where the probability of
finding an electron is zero.
• At a node, 2 = 0
• For an s-orbital, the number of nodes is (n - 1).
Representations of Orbitals
The s-Orbitals

17. The s-Orbitals

18. • There are three p-orbitals px, py, and pz.
• The three p-orbitals lie along the x-, y- and z- axes of a
Cartesian system.
• The letters correspond to allowed values of ml of -1, 0,
and +1.
• The orbitals are dumbbell shaped.
• As n increases, the p-orbitals get larger.
• All p-orbitals have a node at the nucleus.
The p-Orbitals

19. The p-Orbitals
Electron-distribution
of a 2p orbital.

20. • There are five d and seven f-orbitals.
• Three of the d-orbitals lie in a plane bisecting the x-, y-
and z-axes.
• Two of the d-orbitals lie in a plane aligned along the x-,
y- and z-axes.
• Four of the d-orbitals have four lobes each.
• One d-orbital has two lobes and a collar.
The d and f-Orbitals

22. • Orbitals can be ranked in terms of energy to yield an
Aufbau diagram.
• As n increases, note that the spacing between energy
levels becomes smaller.
• Orbitals of the same energy are said to be degenerate.
Orbitals and Quantum Numbers

23. Orbitals and Their Energies

24. • Line spectra of many electron atoms show each line as a
closely spaced pair of lines.
• Stern and Gerlach designed an experiment to
determine why.
• A beam of atoms was passed through a slit and into a
magnetic field and the atoms were then detected.
• Two spots were found: one with the electrons spinning
in one direction and one with the electrons spinning
in the opposite direction.
Electron Spin and the Pauli Exclusion
Principle