Atomic Structure Detailed Notes

ATOMIC STRUCTURE NOTES

1. Periodic Table of the Elements

  • Elements Listed: Basic format of the periodic table with atomic numbers and symbols including:
    • Helium (He)
    • Lithium (Li)
    • Sodium (Na)
    • Magnesium (Mg)
  • Atomic Masses: Each element has an associated atomic mass.
  • Understanding the Layout: Organized by increasing atomic number from left to right.

2. Atom Structure – The Basic Unit of Matter

  • Components of an Atom:
    • Protons: Positively charged particles
    • Neutrons: Neutral particles, found in the nucleus
    • Electrons: Negatively charged particles that orbit the nucleus in shells
  • Atomic Mass Formula: Calculated as protons + neutrons.

3. Electron Shells

  • Shell Configuration:
    • Shell 1: Can hold 2 electrons
    • Shell 2: Can hold 8 electrons
    • Shell 3: Can hold 8 electrons
  • Energy Levels: Electrons at higher shells have more energy.

4. Representing Atoms

4.1. Bohr Diagram
  • Usage: Most common method to illustrate atom structure showing all shells and electrons.
4.2. Lewis Dot Diagram
  • Usage: Highlights bonding by showing only the valence electrons.

5. Identifying Elements

  • Example:
    • Aluminum (Al): 13 Protons, 13 Neutrons, Atomic Mass 26.9815386
    • Calcium (Ca): 20 Protons, 20 Neutrons, Atomic Mass 40.08
    • Neon (Ne): To be filled.

6. Isotopes and Ions

  • Isotopes:

    • Variation of elements based on neutron count (different atomic masses).
    • Example: Aluminum-26

  • Ions:

    • Charged atoms, resulting from the loss or gain of electrons, do not change the element.
    • Example: Lithium ion (Li+)

7. Relationship between Protons, Neutrons, and Electrons

Changing Particles:

  • Protons: Change element identity.
  • Electrons: Change charge of atom (ion formation).
  • Neutrons: Change atomic mass without affecting charge.

8. Nuclear Symbol

  • Format:
    • Mass Number (A) = Total of protons + neutrons
    • Atomic Number (Z) = Number of protons
    • Symbol: Element abbreviation (e.g., Carbon is C, and for Carbon-12 it is written as [^{12}C]).

9. Worked Example 2.1

  • Example a: For neutral atom 19F, determine the neutrons:

    • Formula: n° = A - Z
    • Calculation: n° = 19 - 9 = 10 neutrons

  • Example b: For negative ion 14N 3- (extra electrons):

    • Calculate electrons: e¯ = Z - ionic charge
    • Calculation: e¯ = 7 - (-3) = 10 electrons.

10. Summary Table - Determining Subatomic Particles

  • For Neutral Atom:

    • Proton (p+) = Z
    • Neutron (n°) = A - Z
    • Electron (e¯) = Z

  • For Ion:

    • Proton (p+) = Z
    • Neutron (n°) = A - Z
    • Electron (e¯) = Z - ionic charge

  • For Isotope:

    • Proton (p+) = Z
    • Neutron (n°) = atomic mass - Z
    • Electron (e¯) = Z

Conclusion

  • Mastering atomic structure is essential for understanding chemistry and the behavior of matter.