•What is a model?
•Uses familiar ideas to
explain unfamiliar facts
observed in nature.
•It can be changed if you
get new info.
•Evidence you get about an
object without actually
seeing or touching the
object.
•You get a mental picture or
a model of the object.
• In the 5th century BC,
Democritus believed that
matter could be divided into
smaller & smaller pieces
forever until you got to the
smallest possible piece called
an atom (uncuttable).
•In 1803, Dalton published
his atomic theory from
studying weather & the
composition of air.
• 1) All matter is made of
atoms 2) Different elements
have different kinds of atoms
3) Compounds are formed by
joining atoms of 2 or more
elements.
• He discovered the electron & figured
it was part of an atom.
• Invented the Plum Pudding Model
• The atom was a positively charged
ball with lots of negatively charged
electrons stuck into it like “plums
in pudding.”
•
• In 1908, Rutherford
discovered the nucleus.
• He stated that the atom was
mostly empty space made up
of a positively charged nucleus
with negative electrons
scattered around it.
•
• In his experiment, Rutherford fired a
stream of alpha particles at a sheet of
gold foil and found that:
1. Most of the bullets passed right
through the gold sheet without
changing course which meant that
the gold atoms were made up of
empty space.
•
2. Some bullets bounced back
from the sheet which meant
that like charges repel. The
alpha particles were
positive so the nucleus must
then be positively charged.
•Bohr fixed up Rutherford’s
theory.
•He stated that electrons
orbited the nucleus on
definite paths like the
planets around the sun.
•
•Based on a prediction of
where the electrons
actually are using math
formulas.
•Basic idea of waves.
•Subatomic Particlesparticles smaller than an
atom
•3 Main Subatomic Particles:
Protons, Neutrons,
Electrons
Nucleus
• The tiny center of atom
• 99.9% of atom’s weight is the
nucleus but it is 100,000 times
smaller than the entire atom.
• Like a bee in Yankee Stadium
Protons
•Positively Charged particles
(+)
•Found in nucleus
•Weighs 1 AMU
Neutrons
•Neutral particles
•Found in nucleus
•Weighs 1AMU+
AMU
•ATOMIC MASS UNIT
•Special unit used to
measure the mass of
subatomic particles.
•1 proton = 1AMU
Atomic Number
•Number of protons in
nucleus of atom
•Determines what the
element is
•Hydrogen’s Atomic
number is 1 = 1 proton
•Carbon’s Atomic Number
is 6 = 6 protons
Isotopes
• Atoms of same element that
have the same number of
protons but a different
number of neutrons
• C12- C14- difference2 more neutrons
MASS NUMBER
• Sum of protons & neutrons
• distinguishes one isotope
from another
• Carbon = Mass# 12
6P + 6N= 12 total.
•Uranium238
146N + 92P = 238
Uranium235
143N + 92P = 235
Atomic Mass
• Average mass of all isotopes
of that element, usually a
decimal located on the
bottom of each card.
• Atomic mass of
carbon=12.011
Electrons
• Number of protons = number
of electrons outside nucleus.
• Electron fills cloud. Electrons
can be anywhere within the
space around nucleus
•Electrons are arranged in
energy levels according to
how much energy they
contain
• Electrons with lowest energy
are in level closest to
nucleus.
• Electrons with high energy
are in levels farther from
nucleus.
• Each level can only hold so
many electrons: 1st-2 2nd-8
rd
th
th
3 -18
4 -32
5 -18
Chemical makeup
• Properties of elements
depend on how many
electrons are in the various
energy levels.
• Bonding: some do/some don’t
• Quarks-3particles that make
up protons & neutrons