The smallest particle into
which an element can be
divided and still be the same
Atoms are so small that, until
recently, no one had ever seen
one. But ideas, or theories,
about atoms have been around
for over 2,000 years.
A pure substance that cannot be
separated into simpler substances by
physical or chemical means.
Atoms make up elements.
Elements are made of only one kind of
Elements combine to form compounds.
All matter is made of elements or
compounds, so all matter is made of
A unifying explanation for a broad range
of hypotheses and observations that
have been supported by testing.
Democritus (440 B.C.)
Democritus proposed that if you kept
cutting a substance in half forever,
eventually you would end up with an
He called these particles atoms,
Democritus is an Ancient
Greek philosopher born in
Abdera, Thrace, Greece
He was said to be the first
step toward the current
Hypothesized that all matter is
composed of tiny
indestructible units, called
6. His atomic theory contradicted the idea
that matter can be infinitely divided.
According to him, atoms cannot be divided
In the long run, the object will become so
small and invisible that you cannot divide it
He said that these indivisible invisible
particles are ATOMS. The word atom
means not to be cut or indivisible.
7. TAKE NOTE!
He DID NOT MAKE THE
ATOMIC THEORY. He just
He learned this from the
founder of the atomic theory,
9. Democritus thought that atoms were small, hard
particles of a single material and in different
shapes and sizes.
He thought that atoms were always moving and
formed different materials by combining with each
Aristotle disagreed with Democritus’s idea that
you would end up with an indivisible particle.
Because Aristotle had greater public influence,
Democritus’s ideas were ignored for centuries.
10. John Dalton (1803)
He is best known for his
pioneering work in the
development of modern
11. Scientists knew that
with each other in
to form compounds.
Dalton claimed that
the reason for this was
because elements are
made of atoms.
12. He published his own three-part
1) All substances are made of atoms.
Atoms are small particles that cannot be
created, divided, or destroyed.
2) Atoms of the same element are exactly
alike, and atoms of different elements
3) Atoms join with other atoms to make
13. 5 POINTS of Dalton’s Theory
All matter consists of tiny particles called
atoms. These are indivisible and
All atoms of a given element are identical
in mass and properties.
The atoms of a given element are
different from those of any other element;
the atoms of different elements can be
distinguished from one another by their
respective relative atomic weights.
14. Compounds are formed by a
combination of two or more different
kinds of atoms.
Compounds are pure substances.
They can’t be separated into elements
by phase changes because the atoms
of different elements are bonded to
one another and are not easily
separated from one another.
A chemical reaction results to
rearrangement of atoms.
15. Joseph John “JJ”
•Born on December 18
•Discoverer of electron
•Discoverer of isotopes
16. •Invented the mass
•Proposed first waveguide
•Proposed the Plum pudding
•Awarded the 1906 Nobel Prize
17. •Sometimes visualized as having a cloud of
positive charge, a striking contrast to the most
recent atomic model, which describes the
positive nucleus to be surrounded by an
•Electrons were free to rotate within the cloud
of positive substance.
•These orbits were stabilized in the model by
the fact that when an electron moved farther
from the center of the positive cloud, it felt a
larger net positive inward force, because there
was more material of opposite charge, inside
18. Ernest Rutherford
•Born on August 30
•New Zealand chemist and
•Father of nuclear physics
•Discovered that atoms have
their positive charge
concentrated in a very small
19. •Gold Foil Experiment
•Discoverer of proton
•Awarded Nobel Prize in Chemistry in
•Widely credited as splitting the atom in
•Leading the first experiment to “split
21. EUGENE GOLDSTEIN
•Early investigator of
•Discoverer of anode rays
•Credited with the discovery
• subatomic particle with
an electric charge of +1
• found in the nucleus of
each atom, along with
neutrons, but is also
stable by itself
23. JAMES CHADWICK
• English Nobel laureate in
physics awarded for his
discovery of the neutron.
• Hughes Medal of the Royal
• Nobel Prize for Physics
• Chadwick discovered a previously
unknown particle in the atomic
•Particle became known as electron
because of lack of electric charge
25. • Unlike positively charged alpha particles
(consist of two protons and two neutrons
bound together into a particle identical to
a helium nucleus), which are repelled by
the electrical forces present in the nuclei of
other atoms, neutrons do not need to
overcome any Coulomb barrier and can
therefore penetrate and split the nuclei of
even the heaviest elements.
•subatomic particle with no net
electric charge and a mass
slightly larger than that of a
•usually found in atomic nuclei
- nuclei of most atoms consist of
protons and neutrons, which are
therefore collectively referred to
27. ATOMIC NUMBER AND
• p- proton
• n- neutron
• z- atomic number
• a- atomic mass
28. Atomic number
• the number of protons in the
nucleus of an atom.
H1 = Hydrogen has one proton
29. Atomic Mass
• the sum of the proton and
neutron of an atom
Proton + neutron = atomic mass
30. Additional info.
•Neutrons are all identical to each other,
just as protons are.
• Atoms of a particular element must
have the same number of protons but
can have different numbers of
• When an atom does not have the
same number of protons and neutrons,
it is called an isotope.
Ion is an atom or molecule
where the total number of
electrons is not equal to the
total number of protons, giving
it a net positive or negative
33. PLUM PUDDING MODEL
•Also known as the “Chocolate
Chip Cookie or Blueberry Muffin
•Atom is composed of electrons
surrounded by a soup of
positive charge to balance the
electron’s negative charge, like
surrounded by positively-
34. Bohr’s Model
also known as the
neutrons and protons
are in the nucleus
while the electrons are
orbiting the nucleus
electrons are able to
jump from one orbit to
35. Electron Cloud Model
consists of a dense nucleus composed of
protons and neutrons surrounded by
electrons that exist in different clouds at
the various energy levels.
Erwin Schrodinger and Werner Heisenburg
developed probability functions to
determine the regions or clouds in which
electrons would most likely be found.