History of the atom

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History of the atom
And
The Atom’s Properties

Aristotle and Democritus
◦ Aristotle did not believe in atoms.
 Empty space?
◦ Democritus came up with the word “atom”
from atomos meaning indivisible.
 Thought they were the smallest unit of matter
and could not be broken down.
History of the atom

Joseph Proust
◦ Law of definite proportions
 Whenever two elements combine to make a
compound, they do so in a definite proportion by
mass
 Start of stoichiometry
History of the atom

John Dalton
◦ Dalton’s Atomic Theory
 Matter consists of small particles called atoms.
 All atoms of one particular element are identical
and their properties are identical.
 Atoms are indestructible. In chemical reaction,
the atoms rearrange or combine, but are not
destroyed.
 Atoms of different elements have different
properties.
 When atoms of different elements combine to
form compounds, they combine in a ratio of whole
numbers.
◦ Supports the Law of Conservation of Mass
History of the Atom

Joseph Gay-Lussac and A. Avogadro
◦ Studied ratios of combined gases.
◦ Did not fully understand correct chemical
formulas and atomic masses until Amedeo
Avogadro came along.
◦ Avogadro’s number
 6.02 x 1023
History of the atom
JJ. Thompson
 “Plum pudding model”

◦ Negatively charged particles that could be
removed from the atom.
◦ SUBATOMIC Particles called ELECTRONS.
History of the Atom
Robert A. Millikan
 “Millikan Oil-Drop Experiment”

◦ Determined the mass and charge of an electron
◦ 1.6 x 10 -19C
◦ 9.10 x 10-28 g
1/2000 the mass of a proton
History of the atom
Ernest Rutherford
 “Gold Foil Experiment”

◦ Discovered a NUCLEUS
 And that it was POSITIVELY CHARGED
◦ PROTONS
 Hans Geiger
was his student.
History of the Atom

Niels Bohr
◦ “BOHR MODEL OF THE ATOM”
◦ Orbits and energy levels of electrons
◦ Jump between energy levels- Quantum
mechanics
History of the Atom

Werner Heisenberg

Understood that there are certain parameters
of a particle that can’t be measured
simultaneously.
How can we take measurements of or collect
data about an electron?
Heisenberg said it is physically impossible to
measure simultaneously the exact position
and exact linear momentum of a particle. If
Δx is small then Δpx is large and vice versa.
We cannot measure position, time, velocity of
a particle with precision.



Heisenberg Uncertainty Principle

Basic Equations
C  f
E  hf
h  6.63 x10
 34
J s
c  3.00 x10 m / s
8
Equations

Equations
◦ Energy of a photon:
hc
E  hf 

◦ Momentum of a photon:
E hc h
p 

c c 

Heisenberg’s Uncertainty Principle


Equations:
xp x  h  xp x
h

4
h
4
remember : p  mv
Et 

Mass of an electron = 9.11 x 10-31 kg
Heisenberg Uncertainty Principle
Albert Einstein
 PHOTOELECTRIC EFFECT
 Won the Nobel Prize for this

◦ Collision between a particle of light(photon)
and an electron on the surface of a metal.
◦ Entry doors
◦ Photodiode: Pixel
◦ Video camera tubes
◦ Moon dust
◦ Solar cells
Photoelectric Effect

Parts:
 Nucleus: Neutrons, Protons
 Outer shell: electrons
Properties of the Atom


Properties
http://www.falstad.com/qmatom/
Atomic mass: number of protons and
neutrons
 Atomic number: number of protons
 Isotope: same element different mass.
 Ion: Charged atom. Gained or lost
electrons. Anion-negative Cation-positive

Properties of the Atom

Behavior
◦
◦
◦
◦
◦
Neutral atom when protons = electrons
Ion- different number of electrons
Only electrons move to or from the atom.
Responsible for behavior of atom/element.
Octet rule
Properties of the Atom

Electrons
◦ Quantum behavior
◦ EM spectrum
Properties of the Atom
Electrons in discrete
energy levels.
 n level
 Broken into smaller
levels:

◦ s, p, d, f
Quantum
Mechanics
Quantum Mechanics

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