Download Ch. 1 - What is an atom? History of the atom A) Based on Philosophy

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