Chemistry

• Atom


  An extremely small, electrically neutral particle which has a tiny but massive positive core or nucleus and one or more electrons relatively far outside its nucleus
• Democritus


  • Matter is made up of small particles called "atomos" (indestructible / indivisible / uncuttable particles)
• John Dalton


  Father of the Atomic Theory
• John Dalton's Atomic Theory

  • 1.) All matter is made up of atoms
  • 2.) The element is made up of one kind of atom
  • 3.) Atoms of two or more elements combine to form compounds in ratios of simple whole numbers (Law of Definite Proportion & Law of Multiple Proportion)
  • 4.) An atom cannot be created nor destroyed (Law of Conservation of Matter)
• J.J. Thompson


  • Discovered Electrons (Cathode Ray Tube experiment)
  • Devised the Plum Pudding Model: The atom is a large, positive, solid sphere where negatively-charged particles are embedded in the positively-charged sphere
• Ernest Rutherford


  • Discovered Protons (Alpha Scattering experiment)
  • Devised the Nuclear Model: Atoms are made up of a very dense and positively-charged nucleus surrounded by free moving electrons. In between the nucleus and the electron is almost empty space
• James Chadwick


  • Discovered Neutron (Alpha Particles on Beryllium Experiment)
  • Improved the Nuclear Model: There is already an inclusion of the neutron in the nucleus together with the proton
• Niels Bohr


  • Discovered Energy Levels (a circular path around the nucleus where electrons move without losing energy)
  • Devised the Planetary Model: An atom has a nucleus made up of protons and neutrons with atoms distributed at energy levels moving around the nucleus
• Erwin Schrodinger


  • Proposed the Electron Cloud (the probability of locating an electron around the nucleus)
  • Devised the Electron Cloud Model: An atom consists of electrons moving around a central nucleus without a fixed orbit
• Atomic Models


  • Bowling Ball Model (Democritus and Dalton)
  • Plum Pudding Model (JJ Thompson)
  • Nuclear Model (Ernest Rutherford)
  • Improved Nuclear Model (James Chadwick)
  • Planetary Model (Niels Bohr)
  • Electron Cloud Model (Erwin Schrodinger)
• Proton


  Positively charged particle in the nucleus, discovered by Ernest Rutherford
• Neutron


  Neutral particle in the nucleus, discovered by James Chadwick
• Electron


  Negatively charged particle outside the nucleus, discovered by J.J. Thompson
• The number of Protons, Neutrons, and Electrons determine what type of atom it is
• Atomic Number


  The number of protons in an atom
• Mass Number


  The total number of protons and neutrons in an atom
• The general notation used to represent the mass number and atomic number of an atom is A Z X, where X is the symbol of the element, A is the mass number, and Z is the atomic number