Subatomic Particles and Atomic Models

Subatomic Particles

• Protons:

  • Positively charged particles found in the nucleus of an atom.
  • Mass of approximately 1 atomic mass unit (amu).
  • Number of protons defines the element (atomic number).

• Neutrons:

  • Neutral particles also located in the nucleus.
  • Similar mass to protons (approximately 1 amu).
  • Contribute to the atomic mass; stabilize the nucleus.

• Electrons:

  • Negatively charged particles that orbit the nucleus.
  • Much smaller mass than protons/neutrons (approximately 1/1836 amu).
  • The number of electrons in a neutral atom equals the number of protons.

Atomic Models

• Dalton's Model (1803):

  • Proposed atoms as indivisible and indestructible spheres.

• Thomson's Model (1897):

  • Introduced the "plum pudding" model, suggesting atoms contain negatively charged electrons in a positively charged “soup”.

• Rutherford's Model (1911):

  • Discovered the nucleus through gold foil experiment; proposed that most of the atom is empty space with a dense, positively charged nucleus.

• Bohr's Model (1913):

  • Suggested electrons orbit the nucleus in specific energy levels or shells.
  • Introduced quantized energy levels leading to fixed orbits.

• Quantum Mechanical Model (1920s):

  • Developed from wave-particle duality concepts, representing electrons in probability distributions (electron clouds) rather than fixed paths.

Electron Configuration

• Definition:

  • The distribution of electrons in an atom's orbitals, critical for understanding chemical properties.

• Principles:

  • Aufbau Principle: Electrons fill the lowest energy orbitals first.
  • Pauli Exclusion Principle: No two electrons can have identical quantum numbers within an atom.
  • Hund's Rule: Electrons will fill degenerate orbitals singly before pairing up.

• Notation:

  • Written using subscripts to indicate the number of electrons in each orbital (e.g., 1s² 2s² 2p⁶).
  • Energy levels (n) correspond to principal quantum numbers, while letters (s, p, d, f) represent types of orbitals.

• Electron Configuration Examples:

  • Hydrogen (H): 1s¹
  • Carbon (C): 1s² 2s² 2p²
  • Neon (Ne): 1s² 2s² 2p⁶ (noble gas configuration).

• Valence Electrons:

  • Electrons in the outermost shell involved in chemical bonding, crucial for predicting element reactivity.

Subatomic Particles

• Protons are positively charged particles located in the atom's nucleus.
• Protons have a mass of approximately 1 atomic mass unit (amu).
• The number of protons defines the element (atomic number).
• Neutrons are neutral particles also found in the nucleus.
• Neutrons have a mass similar to protons (approximately 1 amu).
• They contribute to the atomic mass and stabilize the nucleus.
• Electrons are negatively charged particles that orbit the nucleus.
• Electrons are much smaller in mass compared to protons and neutrons (approximately 1/1836 amu).
• The number of electrons in a neutral atom is equal to the number of protons.

Atomic Models

• Dalton's Model (1803) suggested that atoms are indivisible and indestructible spheres.
• Thomson's Model (1897), known as the "plum pudding" model, proposed that atoms contain negatively charged electrons embedded in a positively charged "soup."
• Rutherford's Model (1911), based on the gold foil experiment, discovered the nucleus. He proposed that most of the atom is empty space with a dense, positively charged nucleus.
• Bohr's Model (1913) suggested that electrons orbit the nucleus in specific energy levels or shells.
• Bohr introduced quantized energy levels, leading to fixed orbits.
• The Quantum Mechanical Model (1920s), developed from wave-particle duality concepts, represents electrons in probability distributions (electron clouds) rather than fixed paths.

Electron Configuration

• Electron configuration describes the distribution of electrons in an atom's orbitals, which is crucial for understanding its chemical properties.
• Key Principles:
  • Aufbau Principle: Electrons fill the lowest energy orbitals first.
  • Pauli Exclusion Principle: No two electrons in an atom can have identical quantum numbers.
  • Hund's Rule: Electrons will occupy degenerate orbitals singly before pairing up.
• Notation:
  • Electron configuration is written using subscripts to indicate the number of electrons in each orbital, like 1s² 2s² 2p⁶.
  • Energy levels (n) correspond to principal quantum numbers, while the letters (s, p, d, f) represent types of orbitals.
• Examples:
  • Hydrogen (H): 1s¹
  • Carbon (C): 1s² 2s² 2p²
  • Neon (Ne): 1s² 2s² 2p⁶ (noble gas configuration)
• Valence Electrons:
  • Electrons in the outermost shell are called valence electrons and are involved in chemical bonding. They are crucial in predicting the reactivity of an element.

This quiz covers the foundational concepts of subatomic particles, including protons, neutrons, and electrons, as well as historical atomic models proposed by Dalton, Thomson, and Rutherford. Test your knowledge on the nature of atoms and their components.