Atomic Models and Structure: From Plum Pudding to Bohr

Plum Pudding Model

• The first model to explain the structure of the atom.
• Development was based on the fact that electron mass is significantly smaller than proton mass.
• The nucleus, containing protons, occupies a central space, while electrons are embedded within it.
• This model explains the formation of ions:
  • Anion: An atom that gains electrons, becoming negatively charged.
  • Cation: An atom that loses electrons, becoming positively charged.

Rutherford Model

• Rutherford experimentally proved the Thomson model was not possible.
• He suggested the atom is essentially empty space, with mass concentrated in a small, positive nucleus and electrons revolving around it.
• Discrepancies between electron and proton mass led to the discovery of neutral particles: neutrons.

Bohr Atomic Model

• Problem with Rutherford's model: Electrons spinning at high speeds should emit energy (radioactivity), lose speed, and collapse into the nucleus.
• Bohr's Hypothesis: Electrons revolve around the nucleus in specific, stable orbits without emitting energy.
• Energy Levels:
  • Electrons possess specific energy levels depending on their orbit (higher energy the further they are from the nucleus).
  • Electrons "jump" between orbits by absorbing or releasing energy.

Atomic Properties

• Atomic Number (Z): The number of protons in an atom.
• Mass Number (A): The total number of particles within the nucleus (protons + neutrons).

Atomic Structure and Electronic Configuration

• Electrons are distributed in shells around the nucleus.
• Shells increase in energy as they move further from the core.
• Each shell has a maximum capacity for electrons.
• Shells contain up to 4 subshells or orbitals: s, p, d, f.

Isotopes

Isotopes are atoms of the same element with the same atomic number (Z) but different mass numbers (A) due to a varying number of neutrons.