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

3.4 - Electron Configurations of Atoms

3.4.2 - Electron Configuration Notations

There is a way to represent precisely the electron arrangement in atoms. Let's take a look at the simplest atom, hydrogen.

A hydrogen atom has 1 electron. That electron will occupy the lowest principal energy level, n = 1, and the only sublevel, s. We denote the electron configuration of hydrogen as

Electron configuration notation
Mouseover the image for a description of the symbols.

Similarly,

  • Helium has 2 electrons; the 2 electrons both occupy the s sublevel in principal energy level 1.
    • Helium's electron configuration is 1s2
  • Lithium has 3 electrons; 2 of the 3 electrons occupy the s sublevel in principal energy level 1. The 3rd electron must go in the next available sublevel, 2s.
    • Lithium's electron configuration is 1s2 2s1
  • Beryllium has 4 electrons; 2 of the 3 electrons occupy the s sublevel in principal energy level 1. The 3rd and 4th electrons must go in the next available sublevel, 2s.
    • Beryllium's electron configuration is 1s2 2s2

     

As an exercise, write the electron configuration for the first 20 elements on the periodic table. Then click to check your answers.

(section 3.4.3)

Section 4.8
Arrangement of Electrons in Sublevels ..p91


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