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Atomic Structure & Fundamental Particles
Basic Composition of an Atom
- An atom consists of a central nucleus and electrons revolving around it.
- The nucleus contains:
- Protons: Positively charged particles.
- Neutrons: Neutral particles (no electric charge), with a mass nearly equal to that of a proton.
- Electrons: Negatively charged particles that revolve around the nucleus.
Key Discoveries
- Atomic Nucleus: Discovered by Ernest Rutherford.
- Neutron: Discovered by James Chadwick.
- Radioactivity: Discovered by Henri Becquerel.
Classification and Properties of Particles
Fundamental Particles (Basic building blocks not made of smaller particles):
- Electron: Carries a negative charge.
- Quark: A fundamental particle with fractional charge and fractional spin. (Protons and neutrons are composed of quarks).
- Positron: The antiparticle of the electron; has a positive charge and integral spin.
- Neutrino: A particle with zero (or nearly zero) mass.
- Photon: A particle of light; it is not a part of an atom’s structure.
Composite Particles (Made of fundamental particles):
- Proton: Positively charged; resides in the nucleus.
- Neutron: Neutral; resides in the nucleus.
- Alpha (α) Particle: Carries two positive charges; mass is nearly equal to the nucleus of a helium atom.
- Beta (β) Particle: Carries a negative charge (is a high-energy electron).
- Deuteron: The nucleus of a deuterium atom; not considered a fundamental sub-atomic particle.
Quasiparticles (Collective excitations in a material):
- Phonon: A quasiparticle representing a quantum of lattice vibration; has integral spin.
Special Case:
- Higgs Boson: Also known as the “God Particle”. Its discovery is important because it helps scientists understand why elementary particles have mass.
Atomic Properties and Principles
Atomic Number and Mass Number
- Atomic Number: The number of protons in an atom’s nucleus (defines the element).
- Mass Number: The sum of the number of protons and neutrons in an atom’s nucleus.
- Number of Neutrons = Mass Number – Atomic Number.
- *Example: Plutonium-242 (₉₄Pu²⁴²)*
- Atomic Number (protons) = 94
- Mass Number = 242
- Number of Neutrons = 242 – 94 = 148.
- *Example: Plutonium-242 (₉₄Pu²⁴²)*
- Hydrogen is the only element whose most common isotope has no neutrons in its nucleus.
Key Quantum Principles
- Aufbau Principle: Governs the order in which electrons fill the orbitals in an atom.
- Pauli’s Exclusion Principle: No two electrons in an atom can have the same set of four quantum numbers.
- Hund’s Rule: Every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin.
- Heisenberg’s Uncertainty Principle: It is impossible to determine simultaneously both the position and momentum of an electron with absolute precision.
- Magnetic Quantum Number: Specifies the orientation of an orbital in space.
Nuclear Phenomena
Radioactivity
- Discovery: Discovered by Henri Becquerel.
- Measurement: Measured using a Geiger Counter.
- Types of Radiation:
- Alpha (α) particles: Positive charge.
- Beta (β) particles: Negative charge.
- Gamma (γ) rays: Neutral, high-energy electromagnetic waves.
Nuclide Classification
- Isotopes: Atoms of the same element (same atomic number/protons) with different numbers of neutrons (and thus different mass numbers).
- Isobars: Atoms of different elements (different atomic numbers) that have the same mass number.
- Isotones: Atoms of different elements that have the same number of neutrons.
- Example: ₆C¹⁴, ₇N¹⁵, and ₈O¹⁶ are isotones because they all have 8 neutrons.
Key Figures
- Antoine Lavoisier: Regarded as the Father of Modern Chemistry.
- Ernest Rutherford: Credited with the discovery of the atomic nucleus.
- James Chadwick: Discovered the neutron.
- Henri Becquerel: Discovered radioactivity.
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