Download File - Mr. Henshaw`s Lab

(1) Matter is made of atoms; atoms are
indivisible and indestructible.
(2) All atoms of one element are exactly
identical to one another; atoms of different
elements are different from one another.
(3) Atoms are neither created nor
destroyed in chemical reactions.
(4)Atoms combine to form compounds. A
given compound always has the same
relative number and kind of atoms.
(5) Chemical reactions are needed to
rearrange compounds.
Which one of the following is not one of the
postulates of Dalton's atomic theory?
A. Atoms are made of protons, neutrons, and electrons.
B . All atoms of a given element are identical
C . Atoms are neither created nor destroyed in chemical
reactions.
D . Compounds are formed when atoms of more than one
element combine
E . Each element is composed of extremely small
particles called atoms.
In 1897, J.J. Thomson used a cathode ray
tube to deduce the presence of a negatively
charged particle: the electron
http://www.youtube.com/watch?v=O9Goyscbazk&feature=related
Cathode ray
tubes pass
electricity
through a gas
that is contained
at a very low
pressure.
Which one of the following is not true
concerning cathode rays?
A. They originate from the negative electrode.
B. They travel in straight lines in the absence of electric or
magnetic fields.
C. They impart a negative charge to metals exposed to them.
D. They are made up of electrons.
E. The characteristics of cathode rays depend on the material
from which they are emitted.
 He
knew that the
atom contained +
and – charges.
 The
atom was like
“Plum Pudding”
Electrons scattered
in a cloud of
positively charged
matter
Mass of the
electron is
9.11 x 10-28 g
The oil drop apparatus
1916 – Robert Millikan determines the mass
of the electron: 1/1840 the mass of a
hydrogen atom; has one unit of negative
charge
q was always an integer multiple of the same number,
which was given the symbol "e"
The currently accepted value of e is:
1.602x10-19 C
Knowing e allows the electron mass to be
calculated:
9.11 X 10 -31 kg
electrons x integers = charge
Which of these could be the charge of an object?
A. 0.80 x 10-19 C
B. 2.0 x 10-19 C
C. 3.2 x 10-19 C
D. 4.0 x 10-19 C
The magnitude of the charge on an electron
was determined in the __________.
A. cathode ray tube, by J. J. Thomson
B. Millikan oil drop experiment
C. Dalton atomic theory
D. atomic theory of matter
a) Cathode rays have identical properties
regardless of the element used to
produce them. All elements must contain
identically charged electrons.
b) Atoms are neutral, so there must be
positive particles in the atom to balance
the negative charge of the electrons
c) Electrons have so little mass that atoms
must contain other particles that account
for most of the mass
Alpha particles are helium nuclei The alpha particles were fired at a thin
sheet of gold foil
 Particles that hit on the detecting
screen (film) are recorded

Gold Foil
 Shot a particles at
gold.
 Most pass through.
 Very few deflected
 Giegor
and
Marsden were
scientists who
worked under
Rutherford to carry
out the experiment
Most of the particles passed right through
 A few particles were deflected
 VERY FEW were greatly deflected

Conclusions:
a) The nucleus is small
b) The nucleus is dense
c) The nucleus is positively
charged
d) The atom is mostly empty
space
The gold foil experiment performed in
Rutherford's lab __________.
A. confirmed the plum-pudding model of the atom
B . led to the discovery of the atomic nucleus
C. was the basis for Thomson's model of the atom
D. utilized the deflection of beta particles by gold foil
E. proved the law of multiple proportions
In the Rutherford nuclear-atom model:
A. the heavy subatomic particles reside in the nucleus
B. the principal subatomic particles all have essentially
the same mass
C. the light subatomic particles reside in the nucleus
D. mass is spread essentially uniformly throughout the
atom
Studied
the mass of the nucleus of
the atom and realized there is more
mass than number of protons.
The neutron accounted for the extra
mass.
It was so hard to find because it is
neutral and in the nucleus.
 Studied
the light
emitted from atoms
when excited by
electricity Spectroscopy
 Add Energy – electrons
jump up to a higher
level.
 Remove
Energy –
electrons fall back to
lower level.
Niels Bohr
1913
•Electrons exist on energy levels.
•Like planets orbiting the sun
• Each orbit only contains a set
number of electrons.
•Each orbit possessed a given
quantum of energy.
Bohr’s Atom
electrons in orbits
nucleus
 The
area in
space
surrounding
the nucleus
that has a high
probability of
holding an
electron.
 Schrodinger
developed the
cloud model.
 Atom
still has a
positive nucleus.
 Electron location
based on
probability.
 Created cloud
shapes to show the
most probable
location of an
electron.
HELIUM ATOM
Shell
proton
+
electron
N
N
+
-
neutron
ATOMIC STRUCTURE
Particle
Charge
Mass
proton
+ charge
1
neutron
No charge
1
electron
- charge
nil