2. The AtomThe Atom
From the Greek prefix A- meaning
“not”
And the Greek Root –tomos meaning
“cut””
Together meaning “uncuttable”
The ancient Greeks wanted to learn about
the smallest particle of matter
4. Ancient Greek Model of
Atoms
The ancient Greeks were one of the
earliest cultures to investigate the concept
of the atom.
Democtitus and Aristotle , two Greek
philosophers came up with two alternate
theories
5. Democritus’ “Atom”
DemocritusDemocritus believed that all matter
consisted of extremely small particles that
could not be divided.
He called these particles atoms (from the
Greek “ατοµος”, meaning “uncut” or
“indivisible”).
6. Democritus’ “Atom”
He believed there were different types of
atoms with specific sets of properties. The
atoms in liquids, for example, were round
and smooth, but the atoms in solids were
rough and prickly
8. Aristotle’s “Atom”
Aristotle did not think there was a limit to
the number of times matter could be
divided.
He thought that all substances were built
up from only four elements—earth, air,
fire, and water. These elements were a
combination of four qualities—hot, cold,
dry, and wet.
11. Dalton’s Model of the Atom
Dalton proposed the theory that all matter
is made up of individual particles, called
atoms, which cannot be divided.
All atoms of the same element have the
same mass, and atoms of different
elements have different masses.
12. Dalton’s Model of the Atom
Compounds contain atoms of more than
one element.
He developed a theory to explain why the
elements in a compound always join in the
same way
In a particular compound, atoms of
different elements always combine in the
same way
15. J. J. Thomson’s Model of theJ. J. Thomson’s Model of the
AtomAtom
In Thomson’s experiments with beams of
charged particles in a sealed glass tube
led him to the conclusion that atoms were
made of even smaller particles
Thomson reasoned that if the charge of an
atom is neutral, the atom must contain
particles with both positive and negative
charges in equal amounts.
16. J. J. Thomson’s Model of theJ. J. Thomson’s Model of the
AtomAtom
In Thomson’s experiments with beams of
charged particles in a sealed glass tube
led him to the conclusion that atoms were
made of even smaller particles
Thomson reasoned that if the charge of an
atom is neutral, the atom must contain
particles with both positive and negative
charges in equal amounts.
17. The Thomson ModelThe Thomson Model
In Thomson’s model
of the atom, the
negative charges
were evenly scattered
throughout an atom
filled with a positively
charged mass of
matter. The model is
called the “plum
pudding” model.
19. Rutherford’s Model of theRutherford’s Model of the
AtomAtom
To account for these results, Rutherford
hypothesized that the positive charge of
an atom must be concentrated in a very
small area that he called the nucleus.
Further experiments with other elements
led him to conclude that the positive
charge of an atom is determined by the
number of protons in the nucleus.
Each proton has a charge of +1.
20. Rutherford’s Model of the AtomRutherford’s Model of the Atom
and Gold Foil Testand Gold Foil Test
22. The Bohr Model of the AtomThe Bohr Model of the Atom
In Bohr’s model, electrons move with
constant speed in fixed orbits around
the nucleus, like planets around a
sun.
Electrons gain or lose energy when
they move between orbits or energy
levels. Energy levels are like stairs on
a staircase or shelves in a bookshelf
23. The Bohr Model of the AtomThe Bohr Model of the Atom
Evidence for discrete, unique energy
levels comes from the light given off
when energy is added to the atoms of
an element (such as when fireworks
explode or electricity is added to a
neon light). No two elements have the
same set of energy levels, so the
emission pattern can be used to
identify the element.
27. Schrodinger & Heisenberg’sSchrodinger & Heisenberg’s
Electron Cloud ModelElectron Cloud Model
An electron in an atom can moveAn electron in an atom can move
from one energy level to anotherfrom one energy level to another
when the atom gains or loseswhen the atom gains or loses
energyenergy.
28. Scientists discovered that electrons
are less predictable than in Bohr’s
model of fixed orbits. They use an
electron cloud model to show the
most likely locations for electrons
as they move around the nucleus.
29. The electron cloud represents all
the orbitals in an atom. An orbital is
a region of space around the
nucleus where an electron is likely
to be found. Orbitals come in
different sizes, shapes, and
locations
30. An electron configuration is the
arrangement of electrons in the
orbitals of an atom. The most stable
electron configuration is the one in
which the electrons are in orbitals
with the lowest possible energies
32. The Nature of Science
Each scientist was
correct for his time
and ability to make
observations.
As improvements in
technology came
about, each later
scientist proved the
previous scientist(s)
slightly incorrect.
Now there is a totally
different model of the
atom from the first
model presented by
Thompson.
Only some of the
theories of each
scientist remain.
In general…
33. The Nature of ScienceThe Nature of Science
As the ability toAs the ability to
make bettermake better
observationsobservations
improves, theimproves, the
knowledge mayknowledge may
prove or disproveprove or disprove
what we have heldwhat we have held
to be true into be true in
science.science.
