Chp2

Chp2

1. Development of Atomic Theory

   • Democritus
     • atoms are indivisible particles
   • Dalton's Theory
     • correct
       • matter is made up of small, dense particles called atoms
       • atoms of different element have different masses & sizes
       • atoms cannot change into other atoms
       • chemical reactions are the separation,joining or re-arranging of atoms
       • atoms can combine with other atoms in simple ratios to form compounds
       • atoms of 2 elements can combined in different ratios to form different compounds
     • wrong
       • atoms are indestructible (can divided into proton, neutron, electron)
       • atoms of same element are identical( isotopes, different no. of neutrons)
   • Thomson
     • identical cathode ray were produced by diff. elements
       • these cathode rays were small negative charged particles called electrons
     • plum pudding model
       • 1st: atoms were positively charged spheres containing negatively charged particles
       • then: electrons & protons were distributed evenly throughout an atoms
   • Rutherford
     • most atoms are made up of empty spaces
     • mass & positive charge of atoms is concentrated at nucleus
     • electrons move around nucleus
   • Bohr's Model
     • electron rotates around the nucleus in definite orbit having specific amounts of energy. n=1 has lowest energy
     • only certain shells or energy level can exist. electron cannot be found between shells
     • electrons moving in a shell doesn't radiate energy.
     • electron can change orbit by absorbing or releasing a quantum of energy suitable for that transaction
   • Quantum-Mechanical theory
     • electrons & other sub-atomic particle have a wave nature
     • position of electrons can be calculated using Shrodinger Wave Equation
     • electron's position cannot be precisely define but only given a region of probability