Atomic Theories and the Periodic Table

• Democritus


  Suggested that matter is composed of tiny indivisible particles known as atoms.
• Aristotle


  Suggested that there is no vacuum and that matter is composed of four elements: earth, air, fire, and water.
• Dalton


  (Compact atom)

  1. All matter is composed of tiny, indivisible particles called atoms.
  2. The atoms of any element are the same in mass, volume, and chemical properties.
  3. Atoms of different elements have different properties.
• Thompson


  (Charged atom)

  Atoms contain positive and negative charges.
• Rutherford


  (Nuclear atom)

  The atom has a positive, small, and massive nucleus.
• Bohr


  (Planetary atom)

  The atom contains a nucleus (protons and neutrons) surrounded by shells with electrons.
• Modern model


  (Electron cloud)

  Central positive nucleus and negative electron cloud.
• Atom


  Is the smallest part that keeps the element properties.
• Atomic volume


  Is extremely small that it can be imaged by scanning tunneling microscope (STM) only.
• Electron


  It is a small negative subatomic particle moving around the nucleus.

  Discovered by Thompson using cathode ray tube.
• Electron cloud


  Is an instant shot that describes the movement of an electron around the nucleus.
• Energy Level


  It is the region with a high probability of finding the electron around the nucleus.
• Principle Quantum Number


  Describes the energy level and its volume.

  Takes whole number values (n = 1, 2, 3...).
• Level


  The main energy level (shell) can contain different sublevels (subshells). Sublevels are divided into orbitals, and every orbital can be filled with 2 electrons max.
• Sublevels


  (s) with one orbital and 2 electrons

  (p) with 3 orbitals and 6 electrons

  (d) with 5 orbitals and 10 electrons

  (f) with 7 orbitals and 14 electrons
• Total number of electrons


  Total number of electrons in a particular energy level = 2n^2
• First Energy Level


  No. of Electrons: 2

  1s^2
• Second Energy Level


  No. of Electron: 8

  2s^2 2p^6
• Third Energy Level


  No. of Electron: 18

  3s^2 3p^6 3d^10
• Fourth Energy Level


  No. of Electron: 32

  4s^2 4p^6 4d^10 4f^14
• Aufbau Principle


  Electrons fill lower-energy atomic orbitals before filling higher-energy ones.
• Paulis Exclusion Principle


  Orbitals can be filled by maximum 2 electrons in opposite spins.
• Hunds Rule


  Every orbital in a sublevel is singly occupied before any orbital is doubly occupied.