Atomic History and Subatomic Particles

Atomic History

• Democritus (400 BCE): Proposed the concept of indivisible particles called atoms.
• John Dalton (1803): Developed the atomic theory.
  • Atoms are indivisible (later disproven).
  • Atoms of the same element are identical.
  • Atoms combine in fixed ratios to form compounds.
• J.J. Thomson (1897): Discovered the electron using the cathode ray tube, proposing the plum pudding model (electrons embedded in a positive matrix).
• Ernest Rutherford (1911): Performed the gold foil experiment, discovering the nucleus.
  • Atoms are mostly empty space with a dense, positively charged nucleus.
• Niels Bohr (1913): Proposed electrons travel in specific energy levels around the nucleus.
• Erwin Schrödinger (1926): Developed the wave mechanical model, describing electrons in probabilistic regions called orbitals.
• James Chadwick (1932): Discovered the neutron, completing the atomic model.

Subatomic Particles

• Proton (p+): Charge +1, mass ≈ 1 amu, located in the nucleus.
• Neutron (n0): Charge 0, mass ≈ 1 amu, located in the nucleus.
• Electron (e−): Charge -1, mass ≈ 0.0005 amu, located in the electron cloud.

Isotopes

• Atoms of the same element with different numbers of neutrons.

• Isotope Notation: AZX (e.g., 146C)

  • A: Mass number (protons + neutrons)
  • Z: Atomic number (protons)
  • X: Element symbol

• Calculating Neutrons: Mass Number - Atomic Number

Electron ConfigurationAtomic History

• Democritus (400 BCE): Proposed the concept of indivisible particles called atoms.
• John Dalton (1803): Developed the atomic theory.
  • Atoms are indivisible (later disproven).
  • Atoms of the same element are identical.
  • Atoms combine in fixed ratios to form compounds.
• J.J. Thomson (1897): Discovered the electron using the cathode ray tube, proposing the plum pudding model (electrons embedded in a positive matrix).
• Ernest Rutherford (1911): Performed the gold foil experiment, discovering the nucleus.
  • Atoms are mostly empty space with a dense, positively charged nucleus.
• Niels Bohr (1913): Proposed electrons travel in specific energy levels around the nucleus.
• Erwin Schrödinger (1926): Developed the wave mechanical model, describing electrons in probabilistic regions called orbitals.
• James Chadwick (1932): Discovered the neutron, completing the atomic model.

Subatomic Particles

• Proton (p+): Charge +1, mass ≈ 1 amu, located in the nucleus.
• Neutron (n0): Charge 0, mass ≈ 1 amu, located in the nucleus.
• Electron (e−): Charge -1, mass ≈ 0.0005 amu, located in the electron cloud.

Isotopes

• Atoms of the same element with different numbers of neutrons.

• Isotope Notation: AZX (e.g., 146C)

  • A: Mass number (protons + neutrons)
  • Z: Atomic number (protons)
  • X: Element symbol

• Calculating Neutrons: Mass Number - Atomic Number

Electron Configuration

• Describes the arrangement of electrons in an atom's energy levels.

• Sublevel Filling Order:1s, 2s, 2p, 3s, 3p , 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s...

• Pauli Exclusion Principle: No two electrons can have the same set of quantum numbers.

• Aufbau Principle: Electrons fill lower energy sublevels first.

• Hund's Rule: Electrons occupy orbitals of the same sublevel singly before pairing.

Examples: Carbon (6)

• Electron Configuration: 1s22s22p2

Atomic Models

• Bohr Model: Electrons orbit the nucleus in specific energy levels. Energy is absorbed/emitted when electrons change levels. Limitations exist when dealing with multi-electron systems.

• Wave Mechanical Model: (Schrödinger Model): Electrons exist in orbitals (probabilistic regions), making it more accurate for multi-electron systems.

• Describes the arrangement of electrons in an atom's energy levels.

• Sublevel Filling Order:1s, 2s, 2p, 3s, 3p , 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s...

• Pauli Exclusion Principle: No two electrons can have the same set of quantum numbers.

• Aufbau Principle: Electrons fill lower energy sublevels first.

• Hund's Rule: Electrons occupy orbitals of the same sublevel singly before pairing.

Examples: Carbon (6)

• Electron Configuration: 1s22s22p2

Atomic Models

• Bohr Model: Electrons orbit the nucleus in specific energy levels. Energy is absorbed/emitted when electrons change levels. Limitations exist when dealing with multi-electron systems.
• Wave Mechanical Model: (Schrödinger Model): Electrons exist in orbitals (probabilistic regions), making it more accurate for multi-electron systems.