Ch. 3: Atomic Structure

1
Ch. 3 Atomic Structure

• The Theory of the Atom
• ________________, a famous Greek teacher who
  lived in the 4th Century B.C., first suggested
  the idea of the atom.
• ________ __________ came up with his atomic
  theory based on the results of his experiments.
  (See p. 56)
• The Atom
• The smallest particle of an ________________ is
  an atom.
• The atom is made up of three ________________
  particles.
• The electron was discovered in _______ by J. J.
  Thomson by using a cathode ray tube. The
  electron has a _______ charge. Its mass is much
  smaller than the other 2 subatomic particles,
  therefore its mass is usually ______________.

Democritus
John Dalton
element
subatomic
1897
(-)
ignored
2
Cathode Ray Tube
3
()

• (2) The proton has a ______ charge, and it was
  discovered in _________ by E. Goldstein.
• (3) The neutron does not have a charge. In other
  words, it is ________. It was discovered in ____
  by James Chadwick. The neutron has about the
  same _________ as the proton.
• These three particles make up all the
  ____________________ in the Universe!
• There are other particles such as neutrinos,
  positrons, and quarks, but are typically left for
  2nd year chemistry courses.

1886
neutral
1932
mass
visible matter
4

• Nuclear Atomic Structure
• The atom is made up of 2 parts/sections
• (1) The ______________ --- (in the center of the
  atom)
• (2) The ____________ _________ --- (surrounds
  the nucleus)

nucleus
electron cloud
(p n0)
e- cloud
5

• The Nucleus
• Discovered by Ernest ________________ in
  ________.
• He shot a beam of positively charged alpha
  particles, which are ___________ nuclei, at a
  thin sheet of ______ _____.

Rutherford
1911
helium
gold foil

• 99.9 of the particles went right on through to
  the ______________.
• Some were slightly deflected. Some even
  ____________ ________ towards the source!
• This would be like shooting a cannon ball at a
  piece of tissue paper and having it bounce off.

detector
bounced back
6
Rutherfords Experiment
7
Conclusions about the Nucleus

• (1) Most of the atom is more or less _________
  ___________.
• (2) The nucleus is very _________. (Stadium
  Analogy)
• (3) The nucleus is very ___________. (Large Mass
  Small Volume)
• (4) The nucleus is ______________ charged.

empty space
tiny
dense
positively

• Counting Subatomic Particles in an Atom
• The atomic of an element equals the number of
  ____________ in the nucleus.
• The mass of an element equals the sum of the
  _____________ and ______________ in the nucleus.
  
• In a neutral atom, the of protons of
  ______________.
• To calculate the of neutrons in the nucleus,
  ______________ the ___________ from the
  __________ .

protons
protons
neutrons
electrons
subtract
atomic
mass
8
Practice Problems

• Find the of e-, p and n0 for sodium. (mass
  23)
• Find the of e-, p and n0 for uranium. (mass
  238)
• 3) What is the atomic and mass for the
  following atom? e- 15 n0 16

Atomic 11 e- p
neutrons 23-11 12
Atomic 92 e- p
neutrons 238-92 146
Atomic 15 e- p
Mass p n0 1516 31
The element is phosphorus!
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Isotopes

• An isotope refers to atoms that have the same
  of ___________, but they have a different of
  ___________.
• Because of this, they have different _________
  s (or simply, different ___________.)
• Isotopes are the same element, but the atoms
  weigh a different amount because of the of
  ______________.
• Examples---gt (1) Carbon-12 Carbon-13
• (2) Chlorine-35 Chlorine-37
• (The shown after the name is the mass .)
• For each example, the elements have identical
  ___________ s, ( of p) but different
  _________ s, ( of n0).
• Another way to write the isotopes in shorthand is
  as follows

protons
neutrons
mass
masses
neutrons
atomic
mass
C
Cl
12
35
6
17
mass
atomic
The top number is the ________ , and the bottom
is the __________ number. Calculating the n0
can be found by _____________ the s!
subtracting
10
Figure 3.10 Two isotopes of sodium.
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More Practice Problems

• Find the e-, p and n0 for Xe-131.
• Find the e-, p and n0 for
• 3) Write a shorthand way to represent the
  following isotope
• e- 1 n0 0 p 1

Atomic 54 p e- n0 131 - 54
77
Cu
63
29
Atomic 29 p e- n0 63 - 29 34
Atomic p e- 1 mass n0 p
1 0 1
H-1 or
H
1
1
12
Ions

• An atom can gain or lose electrons to become
  electrically charged.
• Cation (___) charged atom created by
  ___________ e-s.
• Cations are ______________ than the original
  atom.
• _____________ generally form cations.
• Anion (___) charged atom created by
  _____________ e-s.
• Anions are ____________ than the original atom.
• _______________ generally form anions.
• Practice Problems Count the of protons
  electrons in each ion.
• a) Mg2 p _____ e- ______
• b) F-1 p _____ e- ______

losing
smaller
Metals
-
gaining
larger
Nonmetals
12
10
9
10
13
Atomic Mass

• Based on the relative mass of Carbon-12 which is
  exactly _______.
• 1 p __ atomic mass unit (amu) 1 n0 __ amu
  1e- __ amu
• The atomic masses listed in the Periodic Table
  are a weighted average of all the isotopes of
  the element.

12
1
1
0
Weighted Average

• Practice Problems
• (1) Mrs. Smiths geometry semester grades are
  calculated using a weighted average of three
  category scores
• Major Grades 60 of your grade
• Minor Grades 30 of your grade
• Semester Exam10 of your grade
• If a student had the following scores, what would
  they receive for the semester?
• Major 80 (B - )
• Minor 60 (D -)
• Semester Exam65 (D)

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Weighted Average

• Step (1) Multiply each score by the that it
  is weighted.
• Step (2) Add these products up, and that is the
  weighted average!
• 60 x 80 48.0
• 30 x 60 18.0
• 10 x 65 6.5
• Add them up!!
• A normal average would be calculated by simply
  adding the raw scores together and dividing by 3
• 80 60 65 205 3 68.3 D

72.5 (C-)
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Average Atomic Mass

• Practice Problems
• (2) In chemistry, chlorine has 2 isotopes
• Cl-35 (75.8 abundance) Cl-37 (24.23
  abundance)
• What is the weighted average atomic mass of
  chlorine?
• 35 x 0.758 26.53
• 37 x 0.2423 8.9651
• Add them up!!!
• (3) Oxygen has 3 isotopes
• O-16 (99.76) O-17 (0.037) O-18 (0.2)
• Estimate oxygens average atomic mass.

35.4951 amu
Barely over 16.0 amu
16
Average Atomic Mass

• (4) Copper has an average atomic mass of 63.546
  amu.  It contains only two natural isotopes,
  which are Cu-63, with an isotope mass of 62.940
  and Cu-65 with an isotope mass of 64.928.  What
  are the percent of the two isotopes in naturally
  occurring copper?

Avg. Atomic Mass (Cu-63 x Mass Cu-63)
(Cu-65 x Mass Cu-65)
Cu-63 Cu-65 100
Cu-63 Cu-65 1
OR
63.546 (Cu-63 x 62.940) (Cu-65 x 64.928)