Atomic Theory

• John Dalton - the first scientist to develop an atomic theory based on scientific observations.

  He believe that:

  1. All matter is made up of atoms
  2. Atoms cannot be broken down further
  3. Atoms within an element are the same; atoms from different elements are not
• John Dalton - an English scientist. He is often referred to as the Father of Atomic Theory. In 1803, he proposed the theory of the atom
• Compounds - are formed when atoms from two or more elements combine
• Law of Multiple Proportions - states that if two elements combine to form more than one compound, the masses of one element will combine with the other element in a whole-number ratio
• J.J. Thomson - an English physicist who is credited with the discovery of the electron and proposed the "plum pudding" model of the atom
• Part of Dalton's theory was disproved when Joseph John (J.J.) Thomson discovered the electron in 1897. Thomson used the idea of RADIATION energy that is transmitted in the form of waves, particles or rays
• Using electromagnetic radiation theory, Thomson built a CATHODE RAY TUBE to prove that negatively charged particles (electron) were present in atoms
• Cathode ray tube - a closed glass cylinder in which most of the air has been removed
• Inside the Cathode ray tube are two ELECTRODES, a CATHODE which is a negatively charged electrode and a ANODE which is a positively charged electrode
• Cathode - a negatively charged electrode
• Anode - a positively charged electrode
• When a high voltage of is applied between the electrodes, a beam of electrons travels from the anode to the cathode
• Ernest Rutherford - a British physicist, who took Thomson's idea a step further by using radio active particles
• Alpha particles - particles made up of two protons and two neutrons
• Nucleus - positively charged central core of an atom; contains nearly all of its mass
• Ernest Rutherford - a British physicist who named the center of an atom nucleus
• In 1909, Robert Andrews Millikan performed an experiment in which he was able to find the size of the charge on an electron
• Robert Andrews Millikan - am American physicist who received the Nobel Prize in Physics in 1923 for his work on measurement of the elementary electric charge
• The charge of an electron

  
• Unit of an electric charge

  
• Elementary electric charge - the charge of both the electron and proton
• The mass of the proton

  
• James Chadwick - a British physicist who discovered the neutron in 1932. He was awarded the Nobel Prize in Physics in 1935
• The Sub-atomic particles

  A) Proton

  B) Neutron

  C) Electron

  
• Multiple Law of Proportions - it states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in a ratio of small whole numbers. 
• Law of Multiple Proportions - This law supports the idea that elements combine in specific proportions because they are made up of indivisible atoms, each contributing a fixed amount of mass to the compounds they form.