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Chapter 3:
Atoms, the Building
Blocks of Matter
Atomic Theory has Evolved!
Leave a couple of lines!
Law of Conservation of Mass
Mass is neither created nor destroyed during
an ordinary chemical reaction or physical
change.
Remember the Candle Lab:
C25H52 + O2 + E
CO2 + H2O + C + E
Draw a picture and explain
why it happens?
Leave about a half a page for an activity…
Pioneers of the
Atomic Theory
Chapter 3
Observant people have been looking at
matter and pondering why different
phenomenon occur for hundreds of
years.
Early PhilosophersAristotle and Democritus
Didn’t agree!!
Dead Dude #1- Democritus
Ancient philosopher- 460BC
Matter is made of indivisible
particles.
Atomos means “that which
cannot be further broken
down”
Shortcomings
It is a conceptual definition, not based on
science.
Doesn’t talk about subatomic particles.
Dead Dude#2- Dalton
Explained the Laws

John Dalton (early
1800s)

Atom is a solid,
indestructible mass
(like a billiard ball)
All Atomic Theory builds on Dalton’s Law
All matter is made of tiny particles called
atoms.
2. All atoms of a given element are identical in
size, mass and properties Atoms of each
element are different.
3. Atoms cannot be subdivided, created or
destroyed.
4. Compounds consist of atoms of different
elements combined together. Compounds
have constant composition (fixed ratio of
atoms).
5 Chemical reactions involve the
rearrangement of those atoms.
1.
Dead Dude #3
J.J Thomson- 1850
A ball of positive mass
containing a number of
electrons that are
embedded.
Getting the idea that
there are protons and
electrons (nucleus).
Shortcomings
Doesn’t explain the existence of electrons
outside the nucleus or their importance in
bonding.
No neutrons- can’t explain radioactivity or
the existence of isotopes.
What did experiments with the
cathode ray tubes teach us?
Late 1800’s
Discovery of and
experiments using
the cathode ray tube
led to our
understanding of the
electron.
Millikan Oil Drop Experiment
Henri Becquerel- 1897
Researched newly discovered Xrays (Phosphorescence).
Accidently discovered that
uranium emits radiation that could
be measured using photographic
plates.
Discovered Radioactivityelectrically charged particles.
The Dr’s Curie- 1898
Discovered new
elements- Polonium and
Radium.
Very unstable elements
that give off energy.
This led to an understanding of Alpha, Beta
and Gamma particles.
Dead Dude #4

Rutherford Model- 1905
– Mass of the atom is
concentrated in the center of
a positively charged region
called the nucleus.
– The Planetary Model
Gold Foil Experiment- Draw this and leave some room to
write about the experiment.
Shortcomings
Doesn’t place the electrons.
Doesn’t include neutrons.
Bohr Model-1920
Believed that electrons
traveled in precise orbits
around the nucleus of an
atom
Schrodinger Quantum
Mechanical Model.
Describes mathematically
the wave properties of
electrons and other very
small particles
The nucleus is at the center
of the atom and the
electrons are in the electron
cloud.