• All _____________is composed of atoms.
•Definition:
•If an atom were the size of a football field, the nucleus would be the size of a ___________ and nearly all of the mass of the atom is in the nucleus.
•The space around the nucleus and the electron have very, very little mass.
This means that matter is mostly __________!
• Democritus (BC 400) and the “Atomists” debate the “four” elements
(_________, ____________, ______________, ______________.)
•Democritus concluded that matter _________________________into smaller and smaller pieces forever. Eventually, the smallest piece of matter would be found.
• He used the word “___________” to describe the smallest possible piece of matter.
Draw an example of his model of the atom

The Dalton Model 1808
•All elements are composed of _________________________.
•Atoms of the same element are ____________________
( isotopes not known yet).
•Atoms of different elements are ___________________.
•__________________are formed by joining atoms of two or more elements.
Has the model of the atom changed?
How is his different from Democritus? Why do you think so?
Thompson’s “Plum Pudding” Model 1897
• Discovered ___________________________particles coming off a gas known to be neutral.
•Called these “early” electrons, ___________________.
•Predicted that there must be positive particles (_________________) present in equal number to balance negative charges.
•Proposed atoms were made of pudding like positive charges, with negative electrons inside scattered like plums.

DRAW & LABEL THOMSON’S MODEL.
Robert A. Millikan 1909
•Experiments showed that the mass of an electron is smaller than the simplest type of _____________________atom.
• Mass of electron =
•_____________________has a negative charge.
Based on what was learned about electrons, Two other inferences were made about atomic structure:
1. Because atoms are electrically ________________, they must contain a positive charge to balance the negative electrons.
2. Because _________________________________, atoms must contain other particles that account for most of their mass.
How has this model changed from that of Democritus? What major reason lead to this?

Rutherford’s Model 1911
•Fired tiny positive particles at
____________…most went through without change of course. What did this prove?
•Some particles bounced back as if they hit something solid.
•Reasoned that they were repelled by
___________________________________.
•Discovered and proved the existence of the _______________.
•Reasoned that atoms are mostly “empty” space, but with a
____________________with positive charges.
•These deflections were not consistent with _________________________.
Rutherford was forced to discard the Plum Pudding model.
•He reasoned that the only way the alpha particles could be deflected backwards was if
__________________________________________________.
•He thus developed the “planetary model” of the atom which put all the protons in the nucleus and the electrons orbited around the nucleus like planets around the sun.
DRAW & LABEL HIS MODEL Of THE ATOM:
ATOMIC NUCLEUS
•Atoms are electrically neutral because they contain ______________ numbers of protons and electrons.
••Protons have a ___________________charge.
•Mass of Proton = _________________
•The number of protons present determines the _______________________.
•________________________ are electrically neutral.
•Mass of Neutron = _________________

Nuclear Forces
•You would expect a nucleus with like charged protons to repel one another and be very unstable.
•However, when two protons are extremely close to each other, there is a strong attraction between them.
•The short-range _________________, ___________________, and
___________________ forces hold the nuclear particles together .
The Bohr Model 1913
•Amended __________________“planetary” model in 1913.
•Brought the model in line with the regular patterns (spectral series) of
__________ emitted by real ___________________atoms.
•Bohr’s model worked well explaining simple atoms like hydrogen, but didn’t work for more complex atoms.
•Orbiting electrons of circular orbits had discrete radii
(___________________________________________). They each had discrete __________________________ in the emission spectrum.
•Light, he proposed, radiated from atoms only when an electron made a transition from an _____________________ to one closer to the nucleus.
•Electrons travel in defined ______________________around the
_______________.
•The orbits are labeled by an integer, the ______________________ n .
Electrons can jump from one orbit to another by emitting or absorbing energy.

The Modern Atomic Model--Present Day
• Based on wave mechanics, this model proposes that electrons have
______definite path in an atom (unlike ___________model).
•The ________________ location of an electron is based on how much energy it has. The more ______________________an electron has, the farther from the nucleus.
•The small, positively charged _________________ is surrounded by a large space in which there are enough electrons to make the atom neutral.