Unit #1Unit #2Unit #3Unit #4Unit #5Unit #6Unit #7Unit #8Unit #9Unit #10
spacerUNIT # 3  
spacerspacerIntroduction
spacerspacerObjectives
spacerspacerReading

spacer3.1
Structure
spacerof the Atom

spacerAtomic Number - Number of Protons
spacerNumber of Electrons
spacerMass Number - Number of Neutrons
spacer3.2 Isotopes
spacer3.3 Arrangement
spacerof Electrons

spacerThe Bohr Model
spacerBohr Diagram
spacerThe Lewis Electron-dot Symbol
spacerThe Quantum Mechanical Model of the Atom
spacerElectrons in the sublevels

spacer3.4 Electron
spacerConfigura
tions

spacerFilling Order of the Sublevels

spacerElectron Configuration Notations
spacerElectron Configuration for Atoms of the First 20 Elements
spacerElectron Configuration and the Periodic Table
spacer3.5 Atomic Mass
spacerCalculation of Atomic Mass
spacerCalculate the Atomic Mass of Carbon

spacerspacerProblems
spacer1 | 2 | 3
   

Unit #3 ATOMIC STRUCTURE

3.3 - Arrangement of Electrons

3.3.1a - Bohr Diagram

Let's take a look at how to draw Bohr diagrams:

  1. For a hydrogen atom, H, the one electron goes into the first energy level.
    1. Draw a circle and label it with the symbol of the nucleus, H.
    2. Write the number of protons for the nucleus, 1p+.
    3. Draw an arc to represent the first energy level. Label the arc 1e- to represent that there is one electron in this energy level.

  2. For a helium atom, He, the two electrons go into the first energy level.
    1. Draw a circle and label it with the symbol of the nucleus, He.
    2. Write the number of protons for the nucleus, 2p+.
    3. Draw an arc to represent the first energy level. Label the arc 2e- to represent that both electrons reside in this energy level.

  3. For a lithium atom, Li, two of the three electrons go into the first energy level. The third electron goes into the second energy level. This electron in the outer energy level is called the valence electron. The two electrons in the first energy level are called the core electrons.
    1. Draw a circle and label it with the symbol of the nucleus, Li.
    2. Write the number of protons for the nucleus, 3p+.
    3. Draw an arc to represent the first energy level. Label the arc 2e- to represent that 2 of the 3 electrons reside in this energy level.
    4. Draw a second arc to represent the second energy level. Label the arc 1e- to represent that the 3rd electron resides in this outer energy level.

Let's see if you've grasp the idea. You should be able to draw Bohr diagrams for the first 20 elements of the periodic table. Click here to check your diagrams.

Section 4.6
Arrangement of Electrons in Principal Energy Levels ..p87

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