Lecture Notes on Electrons in Atoms

Overview

• Discussion focused on electrons, specifically:
  • Spaces where electrons exist in an atom
  • Valence electrons
  • How to determine the number of valence electrons using the periodic table
  • Drawing electron dot diagrams

Structure of an Atom

• Diagram of an Atom:
  • Nucleus: Contains protons and neutrons.
  • Electron Spots: Represented as circles (energy levels or shells) for potential electron occupancy.
  • Energy Levels/Shells:
    • First shell holds 2 electrons (closest to nucleus).
    • Second shell holds 8 electrons.
    • Third shell (and beyond) also holds 8 electrons but is more complex.

Filling Electron Spaces Using the Periodic Table

• Periodic Table: Helps identify the number of electrons in an atom by looking at atomic number (number of protons).
• Neutral Atoms: Number of protons = number of electrons.

Examples:

1. Hydrogen (H):

   • Atomic Number: 1
   • Electrons: 1 (fills first shell)
   • Valence Electrons: 1

2. Lithium (Li):

   • Atomic Number: 3
   • Electrons: 3
   • Structure:
     • First shell: 2 electrons filled
     • Second shell: 1 electron filled
   • Valence Electrons: 1

3. Sodium (Na):

   • Atomic Number: 11
   • Electrons: 11
   • Structure:
     • First shell: 2 electrons filled
     • Second shell: 8 electrons filled
     • Third shell: 1 electron filled
   • Valence Electrons: 1

Valence Electrons

• Definition: Electrons in the outermost shell.
• Patterns:
  • Hydrogen, Lithium, Sodium: All have 1 valence electron.
  • Atoms in the same column of the periodic table share the same number of valence electrons.

Drawing Electron Dot Diagrams (Lewis Diagrams)

• Electron Dot Diagrams: Show valence electrons visually.
• Example for Group 1 Elements:
  • Hydrogen (H): H•
  • Lithium (Li): Li•

Group 2 Elements (Beryllium, Magnesium)

• Beryllium (Be):

  • Atomic Number: 4
  • Valence Electrons: 2
  • Dot Diagram: Be• •

• Magnesium (Mg):

  • Atomic Number: 12
  • Valence Electrons: 2
  • Dot Diagram: Mg• •

Group 3 Elements (Boron, Aluminum)

• Boron (B):

  • Atomic Number: 5
  • Valence Electrons: 3
  • Dot Diagram: B• • •

• Aluminum (Al):

  • Atomic Number: 13
  • Valence Electrons: 3
  • Dot Diagram: Al• • •

Group 4 Elements (Carbon, Silicon)

• Carbon (C):
  • Atomic Number: 6
  • Valence Electrons: 4
  • Dot Diagram: C• • • •

Group 5 Elements (Nitrogen, Phosphorus)

• Nitrogen (N):
  • Atomic Number: 7
  • Valence Electrons: 5
  • Dot Diagram: N• • • • •

Group 6 Elements (Oxygen, Sulfur)

• Oxygen (O):
  • Atomic Number: 8
  • Valence Electrons: 6
  • Dot Diagram: O• • • • • •

Group 7 Elements (Fluorine, Chlorine)

• Fluorine (F):
  • Atomic Number: 9
  • Valence Electrons: 7
  • Dot Diagram: F• • • • • • •

Noble Gases (Group 8)

• Helium (He):

  • Atomic Number: 2
  • Valence Electrons: 2 (full shell)

• Neon (Ne):

  • Atomic Number: 10
  • Valence Electrons: 8 (full shell)

• Argon (Ar):

  • Atomic Number: 18
  • Valence Electrons: 8 (full shell)

Summary

• Key Points:
  • Valence electrons indicate chemical reactivity.
  • Atoms in the same periodic table column have similar valence electron counts which dictate their behavior in reactions.
  • Understanding this helps predict chemical bonding and reactivity.