1. Unit 2 – Atomic Structure
Part II – Electron Configuration, EM Spectrum, & Planck’s Law

2. Unit 2 Part 2 Key Terms
Emission Spectrum - The range of all possible wave frequencies of electromagnetic radiation, waves created by the systematic interactions of oscillating electric and magnetic fields
Energy Level – discrete regions of space around the nucleus in the electron cloud where electrons can reside
Excited state - The state of an atom when one of its electrons is in a higher energy orbital than the ground state.
Gamma radiation - Electromagnetic radiation emitted during radioactive decay and having an extremely short wavelength
Ground state - The lowest energy state of an atom or other particle

3. Unit 2 Part 2 Key Terms (cont.)
Lewis dot structure -A model that uses electron-dot structures to show how electrons are arranged in molecules. Pairs of dots or lines represent bonding pairs
Noble gas configuration -An electron structure of an atom or ion in which the outer electron shell contains eight electrons, corresponding to the electron configuration of a noble gas, such as neon or argon
Orbital notation (diagram) -A way to show how many electrons are in an orbital for a given element. They can either be shown with arrows or circles
Planck’s constant - As frequency increases, the energy of the wave increases

4. Quantum Mechanical Model of Atomic Structure
1900: Max Planck – Develops law correlating energy to frequency of light
1905: Albert Einstein – Postulates dual nature of light as both energy and particles
1924: Louis de Broglie – Applies dual nature of light to all matter
1927: Werner Heisenberg – Develops Uncertainty Principle stating that it is impossible to observe both the location and momentum of an electron simultaneously
1933: Erwin Schrodinger – Refines the use of the equation named after him to develop the concept of electron orbitals to replace the planetary motion of the electron

5. Number of electrons (2n2)
Energy Levels
Energy levels correspond to the energy of individual electrons. Each energy level has a discrete numerical value.
Different energy levels correspond to different numbers of electrons using the formula 2n2 where “n” is the energy level
Energy Level
Number of electrons (2n2) 1
2(12) = 2 2
2(22)= 8 3
2(32)= 18 4
2(42)= 32 n
2n2

6. Orbitals Impossible to determine the location of any single electron
Orbitals are the regions of space in which electrons can most probably be found
Four types of orbitals
s – spherically shaped
p – dumbbell shaped
d – cloverleaf shaped
f – shape has not been determined
Each additional energy level incorporates one additional orbital type
Each type of orbital can only hold a specific number of electrons

7. Total # of electrons per orbital type
Orbital Types
Orbital Type
General Shape
Orbital
Sublevels
# of electrons
per sublevel
Total # of electrons per orbital type s
Spherical 1 2 p
Dumbbell 3 6 d
Clover leaf 5 10 f
unknown 7 14

8. Electron Configuration
Energy Level
Orbital Type
Orbital
Sublevel
# of orbitals per energy level (n2)
# of electrons per orbital type
# of electrons per energy level (2n2) 1 s 2 p 3 4 6 8 d 5 9 10 18 f 7 16 14 32

9. Electron Configuration Notation
Find the element on the periodic table
Follow through each element block in order by stating the energy level, the orbital type, and the number of electrons per orbital type until you arrive at the element. 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p

10. Samples of e- Configuration
Element Electron Configuration
H 1s1
He 1s2
Li 1s2 2s1
C 1s2 2s2 2p2
K s2 2s2 2p6 3s2 3p6 4s1
V 1s2 2s2 2p6 3s2 3p6 4s2 3d3
Br 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 (Note the overlap)
Pb 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p2

11. Noble Gas Electron Configuration Notation
Find element on the Periodic Table of Elements
Example: Pb for Lead
Move backward to the Noble Gas immediately preceding the element
Example: Xenon
Write symbol of the Nobel Gas in brackets
Example: [Xe]
Continue writing Electron Configuration Notation from the Noble Gas
Example: [Xe] 6s2 4f14 5d10 6p2

12. Valence Electrons
The electrons in the highest (outermost) s and p orbitals of an atom
The electrons available to be transferred or shared to create chemical bonds to form compounds
Often found in incompletely filled energy levels

13. Valence Electrons
Shortcut to finding valence electrons for main group elements
Family 1A (1) valence electron
Family 2A (2) 2 valence electrons
Family 3A (13) 3 valence electrons
Family 4A (14) 4 valence electrons
Family 5A (15) 5 valence electrons
Family 6A (16) 6 valence electrons
Family 7A (17) 7 valence electrons
Family 8A (18) 8 valence electrons
Family 3-12 have multiple possibilities and shortcuts do not work

14. Electron Dot Notation
Electron configuration notation using only the valence electrons of an atom.
The valence electrons are indicated by dots placed around the element’s symbol.
Used to represent up to eight valence electrons for an atom. One dot is placed on each side before a second dot is placed on any side.
Valance Electrons:
Sodium Magnesium Chlorine Neon
Electron Dot Notation:
  • • •• ••
Na Mg : Cl : : Ne :
• • ••
Oxidation Numbers:

15. Unit 2 Part III Key Terms
Emission spectrum: The range of all possible wave frequencies of electromagnetic radiation, waves created by the systematic interactions of oscillating electric and magnetic fields
Energy Levels - A certain volume of space around the nucleus in which an electron is likely to be found. Energy levels start at level 1 and go to infinity.
Excited state: The state of an atom when one of its electrons is in a higher energy orbital than the ground state.
Gamma radiation: Electromagnetic radiation emitted during radioactive decay and having an extremely short wavelength
Ground state: The lowest energy state of an atom or other particle
Planck’s constant: As frequency increases, the energy of the wave increases

16. Electromagnetic (EM) Spectrum
The EM Spectrum is the range of all possible wave frequencies of electromagnetic radiation, waves created by the systematic interactions of oscillating electric and magnetic fields
The general term for all electromagnetic radiation is light
The range of the EM Spectrum is from very low frequency known as radio waves to very high frequency known as gamma radiation
The visible spectrum of light is in the center portion of this EM Spectrum
All EM Spectrum travels at the same speed in a vacuum – this speed is known as the speed of light, 3.00 x 108 m/s

17. EM Spectrum
Image used courtesy of

18. Speed of Light and Frequency
Since the speed of all EM radiation is the same, there is a clear mathematical relationship between the frequency of the light and its wavelength
All waves travel at a speed that is equal to the product of its frequency (the reciprocal of time) and its wavelength (distance)
c = f λ
The speed of EM radiation is fixed at 3.00 x 108 m/s
Therefore:
3.00 x 108 m/s = f λ
Speed of light = frequency x wavelength
As frequency increases, wavelength decreases. As wavelength increases, frequency decreases
Example: If frequency doubles, wavelength is cut in half

19. As f ↑, λ↓: Calculations
If the wavelength of a radio wave is 15 meter, what is its frequency?
3.00 x 108 m/s = f (10 m)
(3.00 x 108 m/s) / 15 m = f
2.0 x107 s-1 = f
Frequency = 2.0 x107 Hertz
If the frequency of gamma radiation is 6.25 x 1022 Hertz, what is its wavelength?
3.00 x 108 m/s = (6.25 x 1022 s-1) λ
(3.00 x 108 m/s) / (6.25 x 1022 s-1) = λ
4.80 x10-15 m = f
Wavelength = 4.80 x10-15 m

20. As frequency increases, the energy of the wave increases
Planck’s Law
Max Planck determined in 1900 there was a mathematical relationship between the energy of EM radiation and the frequency of that radiation:
As frequency increases, the energy of the wave increases
E = h f
Energy = Planck’s constant x frequency
E = (6.63 x Joule seconds) f

21. Planck’s Law Calculations
Example: If the wavelength of green light is 5.21 x 10-7 meters, what is the energy of this light?
3.00 x 108 m/s = f (5.21 x 10-7 m)
(3.00 x 108 m/s) / 5.21 x 10-7 m = f
5.76 x1014 s-1 = f
Frequency = 5.76 x1014 Hertz
E = (6.63 x Joule seconds) (5.76 x1014 s-1)
E = 3.82 x10-19 Joules

22. Implication of Planck’s Law
In order to move an electron to a higher energy level, excite an electron, energy must be absorbed to move the electron
Since electrons exist in fixed energy levels with a specific amount of energy, the amount of energy needed is a finite amount equal to the difference in the energy associated with the ground state of the electron and the energy associated with the level to which the electron is excited
If the energy related to the excited electron is removed, the electron will return to its ground state and the energy released is equal to the energy absorbed to excite it
The energy released is released as light
The overall result is that every element has a unique spectra of light associated with it and the spectra can be used to identify the element