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Transcript
Bell Ringer
1) Get out your Ch. 5 book pages
and your notes we started.
Schedule
1. Bell Ringer
2. CH. 5 Notes
3. Flame Test Pre-lab
HOMEWORK: Print Ch. 5 Notes
I CAN……solve chemistry problems
by being an independent, creative
thinker.
Teachers open the door, but you must
enter by yourself. 
Dalton
• Proposed model for atom
• Dalton’s Atomic Theory
Elements composed of atoms
Atoms of same elements are alike in mass and size***
Atoms of different elements have different mass and size
Chemical compounds are formed by the union of two or
more atoms of the different elements
– Atoms combine to form compounds in simple numeric
ratios
– Atoms of two elements may combine in different ratios to
form more than one compound
–
–
–
–
• Modifications to Dalton’s original theory:
– Atoms are composed of subatomic particles
– ***Not all atoms of same element have the same mass
– Under certain circumstances, atoms can decompose
Use of Models
• Models are used to explain behavior
• Dalton’s Atomic Model:
– Explains behavior of atoms, compounds
and molecules
• Modifications made when new
information arises
Law of Definite Composition
• Compounds contain two or more elements
chemically combined in definite proportions by
mass
• Water is always a 1 : 2 ratio, oxygen to hydrogen
• Hydrogen peroxide is always a 2 : 2 ratio, oxygen
to hydrogen
Law of Multiple Proportions
• Atoms of two or more elements may
combine in different ratios to produce
more than one compound
• CuCl CuCl2
• CH4
C8H18
Significance of the two
Laws…why are they so
important???
• Composition of a substance will
ALWAYS be the same
• Composition of different compounds
formed from the same elements will
be unique
Law v. Model
• Law
– Summary of observed behavior
– Remain constant
• Model (theory)
– Attempt to explain the observed behavior
– Can be modified
Electric Charge
•
•
•
•
•
Positive
Negative
Unlike charges attract
Like charges repel
Charge may transfer form one object to another:
induction or contact
– Induction: influence of a charged object, NOT
BY CONTACT
Force, charge and distance
F = kq1q2
r2
Ions
( Faraday and Arrhenius)
• Positive = cations
• Negative = anions
• Gain or transfer of electrons (Stoney /
Thomson)
Subatomic Particles
• Electron (Thomson) e– Negative charge
– Mass 9.11 x 10-28 g
• Proton (Goldstein,
Thomson) p+
– 1.637 x10 -24 g
– Positive charge
• Neutron (Chadwick) n°
– Neutral charge
– 1.675 x10 -24 g
Rutherford and the Nucleus of
the Atom
• Gold Foil Experiment
Top: Expected results:
alpha particles passing
through the plum
pudding model of the
atom undisturbed.
Bottom: Observed
results: a small
portion of the particles
were deflected,
indicating a small,
concentrated positive
charge. Note that the
image is not to scale;
in reality the nucleus
is vastly smaller than
the electron shell.
Atomic Arrangement
• What makes
an atom
neutral?
• Same
number of
protons and
electrons
What do the numbers mean?
• Atomic # = # p+
• Whole number increasing from left to
right on the periodic table
• # p+ = # e• Mass number = n° + p+
Isotopes
• Atom with same
atomic number
and different
numbers of
neutrons in
nucleus of atom
Isotopes
• Most elements occur in nature as
mixtures of isotopes
• Not all are stable
• Radioactive isotopes
• Decompose
Atomic Mass
• Atomic mass or atomic weight
• Measured in atomic mass units or amu
• Atomic mass is average relative mass
of all naturally occurring isotopes of
that element
• The atomic mass of an element is
compared to the atomic mass of
carbon-12 (12.00 amu)