1. Electron Arrangement
Unit 3

2. NC Essential Standards
Chm.1.1.2
• Analyze diagrams related to the Bohr model of the hydrogen atom in terms of allowed, discrete energy levels in the emission spectrum.
• Describe the electron cloud of the atom in terms of a probability model.
• Relate the electron configurations of atoms to the Bohr and electron cloud models.
Chm.1.1.3
• Understand that energy exists in discrete units called quanta
Describe the concept of ground and excited states of electrons in an atom
1. When an electron gains an amount of energy equivalent to the energy difference, it moves from its ground state to a higher energy level.
2. When the electron moves to a lower energy level, it releases an amount of energy equal to the energy difference in these levels as electromagnetic radiation (emissions spectrum).
• Articulate that this electromagnetic radiation is given off as photons.
• Understand the inverse relationship between wavelength and frequency, and the direct relationship between energy and frequency.
• Use the “Bohr Model for Hydrogen Atom” and “Electromagnetic Spectrum” diagrams from the Reference Tables to relate color, frequency, and wavelength of the light emitted to the energy of the photon.
• Explain that Niels Bohr produced a model of the hydrogen atom based on experimental observations. This model indicated that:
1. an electron circles the nucleus only in fixed energy ranges called orbits;
2. an electron can neither gain or lose energy inside this orbit, but could move up or down to another orbit;
3. that the lowest energy orbit is closest to the nucleus.
• Describe the wave/particle duality of electrons.

3. Essential Standard 1.3.2

4. Energy is related to the Electron’s orbits
Overview
Energy is related to the Electron’s orbits
When an atom is:
The electron will:
Start at the
Jump to
Number of jumps is related to
Key researchers: Bohr, Plank, Einstein
Schrodinger

5. Bohr’s Model of the Atom
Electrons orbit the nucleus at:
Electrons can be excited by:
When excited, an electron will absorb only a certain amount of energy, (

6. Bohr’s model When excited, the electron
Called the _________ state
The electron does not stay in the excited state but falls back toward the nucleus and releases

7. Bohr’s model

8. 8

9. 9 9

10. Bohr’s model Ground vs. excited state
Number of electrons that exist at specific energy levels
Bohr’s model works for hydrogen but not for the complex atoms

11. Development of the Modern Atomic Model
Here are several models of the atom as they were developed in history:
Development of the Modern Atomic Model

12. Electron Cloud Model Quantum Mechanical Model
Based on determining the probable location of the electron
Within the boundary of the
atom, its electrons can be
found 90% of the time
(based on probability)

14. Methods for Writing Electron Arrangements
Orbital notation
Electron configuration
Noble gas notation
How are you going to remember the names
for each method of writing the electron arrangement?

15. Rules for Electron Arrangement
Aufbau:
Place the electron at the lowest energy orbital possible. *
Pauli’s exclusion principle: Place a maximum of 2 electrons in each orbital.
Hund’s rule: Place an electron in each orbital of a sublevel before pairing up.
* Check the diagram for the order of increasing energy level

16. Electron Arrangement Diagram
n= principal energy level
Sublevels – s, p, d, f
Orbitals
Each orbital holds 2 electrons with opposite spins, shown by arrows:

17. Energy Diagram n = principal energy level Sublevels: Orbitals
Electrons & spin
Increasing Energy
Nucleus

18. SPUD Farm
Memory tool

19. Principal Energy Level
Location of the
Valence electrons

20. Energy Diagram n = principal energy level Sublevels: Orbitals
Electrons & spin
Increasing Energy
Examples: Sulfur & Iron
Nucleus

21. Energy Diagram Students: Phosphorus Calcium Krypton
n = principal energy level
Sublevels:
Orbitals
Electrons & spin
Increasing Energy
Students:
Phosphorus
Calcium
Krypton
Nucleus

22. Energy Diagram n = principal energy level Sublevels: Orbitals
Electrons & spin
Increasing Energy
Nucleus

23. Energy Diagram n = principal energy level Sublevels: Orbitals
Electrons & spin
Increasing Energy
Nucleus

24. Orbital Notation
The orbital is indicated by a line____ wioth the name written below.
Arrows represent the electrons.
Examples
Ne: ___ ___ ___ ___ ___
1s 2s 2p 2p 2p
___ ___ ___ ___ ___ ___ ___ ___ ___ ___
Note: You must write both the lines and the orbital designations under the lines

25. Electron Configuration
Element
Atomic #
Orbital diagram
Electron Configuration H He Li Be B C N O F Ne Na

26. Practice Orbital Notation Element Atomic # (Z) ___ H 1s He ___ ___ Li
___ ___
1s s
1s 2s
___ ___ ___ ___ ___
1s 2s 2p 2p 2p
Element Atomic # (Z) H He Li Be B

27. Practice C N O F Ne
___ ___ ___ ___ ___
1s s 2p 2p 2p
1s 2s 2p 2p 2p

28. Electron Configuration
Principal energy level + sublevel
Use superscripts to show number of electrons in each sublevel
1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

29. Electron Configuration: Sublevel diagram
Determining order: Aufbau rules
n=1
n=2
n=3
n=4
n=5
see figure 5-19 on p.138
Know how to
make this chart!

30. Electron Configuration
Element
Atomic #
Orbital diagram
Electron Configuration H He Li Be B C N O F Ne Na

31. Check your electron configuration answers using the Periodic Table
S, P, D, F
Blocks
Periods 18

32. Valence Electrons
Electrons in the outermost (highest) principal energy level
Important
Participate in bonds to make compounds
1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
1s² 2s² 2p⁶ 3s² 3p⁴
1s² 2s² 2p⁶ 3s¹
1s² 2s²
1s¹

33. Review: Electron Configuration
Write
Potassium
Aluminum
Chlorine
Circle the valence electrons.

34. K Al Cl Electron Dot Notation Represents valence electrons
Maximum number = 8
Octet rule: atoms will lose, gain or share electrons to have 8 valence electrons & become stable

35. Introducing Noble Gas Notation
Analyze the following examples and propose the rules for writing Noble Gas Notation.
chlorine [Ne] 3s²3p⁵
iron [Ar] 4s²3d⁶
zinc [Ar] 4s²3d¹⁰
barium [Xe] 6s²

36. Noble Gas Notation Short cut method for electron arrangement
Use the noble gas in the period above the element
Example:
Na 1s² 2s² 2p⁶ 3s¹
Use Neon
Represent neon’s configuration 1s² 2s² 2p⁶
as [Ne]
- Use in Na: [Ne] 3s¹

38. Noble Gas Notation 1s² 2s² 2p⁶ 3s² 3p⁴ Element 1s² 2s² 2p⁶ 3s² 3p⁶

39. Noble Gas Notation Element 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹º4p⁵

40. Noble Gas Notation 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹º 4p⁶ 5s²4d¹⁰ 5p⁵

41. Periodic Table: Order based on Electron Configuration
Identify element
Write atomic number (Z)
Symbol
Circle or highlight the valence electrons
Write the electron dot notation

43. Write the Electron Dot in the correct location for the element

46. Electron Configuration
Aufbau is the Rule.
Note: However, sometimes the electron configurations are written in energy level sequence rather than Aufbau sequence.
This is mostly used for the “d” sublevel.
Aufbau sequence
Ti: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d²
Energy level sequence
Ti: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d² 4s²