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Ch. 1 - What is an atom? History of the atom A) Based on Philosophy 1. Democritus (460-370 BC) matter made up of tiny indivisible particles called atoms matter is discontinuous ex. pencil 2. Aristotle (384 - 322 BC) matter made up of 4 elements (air, water, fire, earth) matter is continuous ex. pencil B) Based on Science 1. Dalton 2. J.J. Thomson 3. Rutherford Rutherford and the Gold Foil Experiment (McGill U., 1911) Radioactive substances can give off alpha (+), beta (-) and gamma (neutral) radiation Rutherford bombarded gold foil with alpha (+) particles The design: The results: 1- ________ alpha particles ( α ) ___________________________________________. They are __________________________________. 2- _________________ α particles are ________________________________. 3- _________________ α particles ___________________________________! 4*- When a metal with a higher atomic mass was used, more alpha particles were deflected. Conclusions: 1- Since the majority of α particles went through the foil undeflected: The atom must be ___________________________________________________________________. 2- α particles that were deflected have gone close to a ___________________________________________________________________. 3- Since few α particles were deflected the nucleus ___________________________________________________________________. (100 000 X smaller than atom; fly in Olympic Stadium) 4*- Electrons move around nucleus. Rutherford’s Atomic Model The nucleus contains positively (+) charged particles called __________________ The atom is __________________. There has to be an equal number of negatively (-) charged particles called ___________________ circling the nucleus so the charges cancel each other out. Problems with Rutherford’s Model .... Bohr to the rescue! 1- How can positive particles (protons) co-exist in a tiny space when they should repel each other? _______________________________________________________________ 2- How can negatively charged electrons move around a positively charged nucleus without being pulled into it? _______________________________________________________________ - white light is broken into the electromagnetic spectrum Bohr’s conclusions: electrons could occupy specific orbits (energy levels, shells) electrons could jump orbits when energy (heat or electricity) is supplied When an electron falls back to its original orbit it gives off the energy in the form of coloured light. Rutherford-Bohr Model of the atom characteristics: 1- ____________________________________________________________ 2- ____________________________________________________________ 3- ____________________________________________________________ Drawing the first 20 elements: 1- Look at the atomic # a) atomic # = _______________________________ b) # of protons = ____________________________ ex. Carbon: ____ protons = _____ electrons 2- Place protons in __________________ 3- Electrons fill _________________________________________________ # electrons = 2n2 1st level: 2nd level: 3rd level: 4th level: Practice: beryllium chlorine calcium phosphorus __________ __________ __________ __________ The Simplified Atomic Model (Similar to Rutherford-Bohr except...) (ENRICHED) Chadwick discovered the ____________________ It is in the ________________________ It holds protons together It is ________________________ The number of Neutrons is determined by The Atomic Mass can also be determined by Practice: element symbol #e- #p boron chlorine hydrogen helium Practice drawing Simplified Atomic Models: lithium oxygen argon sodium #n