1. 4.1 NOTES The History of the Atom

2. I. Early Theories of Matter
A. The philosophers
1. Democritus: First person to propose the idea of the atom; Atomos means indivisible b/c thought the atom could not be furthered divided (it was the smallest piece of matter possible).
2. Aristotle: Claimed there were 4 elements earth, wind, fire, water
Lavoisier - father of modern chem. – called H and O elements

3. B. John Dalton and his atomic theory:
Billiard ball model of the atom: Father of the Modern Atomic Theory
Five principles:
all matter composed of extremely small particles called atoms
all atoms of a given element are identical and atoms of a specific element are different from those of any other element
atoms cannot be created, divided or destroyed
different atoms combine in simple whole-number ratios to form compounds
in a reaction, atoms are separated, combined or rearranged
Flaws w/ theory – #2 (isotopes) and #3 (subatomic particles)

4. Dalton

5. C. Defining the atom What truly defines an atom? 1. Size
Diameter – 1.28 x 10-10m
World Population – 6,000,000,000
Atoms in a Penny – 29,000,000,000,000,000,000,000
2. Seeing the atom
Scanning Tunneling Microscope
Can see shapes and patterns around atoms
3. Field of nanotechnology
The potential for molecular manufacturing – new materials and chemicals

7. II. Subatomic Particles and the Nuclear Atom
1. Crookes and the cathode ray tube
Cathode ray tube is a glass tube in which most of the air (and matter) has been removed. Metal electrodes are found on each end of the tube with an electrode attached to the negative battery terminal (cathode) and one attached to the positive terminal (anode). Beams of energy travel from the cathode towards the anode are known as cathode rays.

8. 2. J.J. Thomson
Found the beam of energy produced in the cathode ray could be deflected with magnets and he was able to determine the beam was composed of negatively charged particles and he called these particles electrons (0e-1).
Plum Pudding Model
Disproved Dalton’s theory of the atom with the discovery of the first subatomic particle.
The atom is a solid sphere of positive charge and the negatively charged electrons are embedded within the solid sphere.
Today might be called the chocolate chip cookie dough model.

10. 3. Millikan’s oil drop experiment
Determined Terminal Velocity
Which helped determine size and
Charge.

11. B. The nuclear atom Ernest Rutherford and the nucleus –
Placed alpha particles in lead and “shot” them
at a piece of Au foil (malleability of metals!). Around foil placed a fluorescent screen. Found most of the particles went straight through and a small percentage was slightly to completely deflected.
Conclusions:
the nucleus (small, dense charged core) must be located in the center of the atom
the atom is mostly of space.

13. C. Completing the atom
1. Protons: positively charged; amu (mass) of 1; abbreviated - 1p1 or p+
Moseley – used x-rays and discovered each element has a unique number of protons that never changes – known as atomic number

14. 2. James Chadwick and the neutron: Discovered neutron using a beam of energy produced by Be (much like Thomson used the cathode ray) and found the beam could not be deflected by magnets. Conclusion – beam was neutral and he called the neutral particles the neutron. Abbreviated - 1n0 or n0
3. Nucleus contains __protons and neutrons____.

15. Bohr suggested the planetary model of the atom
. Bohr suggested the planetary model of the atom. According to the planetary model, the electrons “orbit” the nucleus. He studied the energy levels for hydrogen extensively to develop his model.

16. TIMELINE!