Atomic Structure Chapter 3

1

• Atomic Structure (Chapter 3)
• Atom- The smallest particle of an element that
  retains the _______________of the element.
• Early Atomic Theory (pgs. 67-69 of text)
• 1. Democritus (around 400 B.C.) stated that the
  world was composed of 2 things empty space and
  small particles. He called these particles
  _________. He stated that the atom was the
  smallest particle possible for a form of matter.
  Aristotle refuted Democritus view and stated
  that all matter was continuous (this view held
  until Newton brought back the atomic viewpoint).
• 2. John Dalton (English Scientist) - was the
  first to propose an atomic theory based upon
  ________________ evidence. His theory was based
  upon the experimental evidence from the work of
  French scientists Antoine Lavoisier (discovered
  the law of conservation of ______) and Joseph
  Proust (discovered what Dalton referred to as the
  law of definite proportions).
• Daltons Atomic Theory
• 1. All elements are composed of tiny particles
  called __________.
• 2. Atoms of the same element are
  ____________(not true). The atoms of one element
  are different than those of another element.
• 3. Atoms cannot be subdivided created or
  destroyed (not true)
• 4. Atoms of different elements can combine with
  one another in _________ ratios by
• mass. This is called the Law of
  Definite Proportions. An example of the Law of
  Definite Proportions The ratio of the mass of
  Sodium to Chlorine in Sodium Chloride is always
  22.990g/35.453 g. This ratio holds regardless of
  the ______ of the sample.
• 5. Chemical reactions occur when _______ are
  separated, joined, or rearranged.
• However, the atoms of an element are
  not changed into________ of another element by
  the chemical reaction.

properties
atoms
experimental
mass
atoms
identical
fixed
size
atoms
atoms
2

• Law of Multiple Proportions (this was not based
  upon experimental evidence, but upon the other
  points of Daltons atomic theory). Whenever __
  elements form more than __ compound, the ratio of
  mass of an element present in each compound, for
  a given mass the other element present in each
  compound, is in a ratio of small ________
  numbers.
• Example of the Law of Multiple Proportions
  Hydrogen can react with Oxygen to form more than
  __ compound. These compounds are _____ (water)
  and _______ (Hydrogen Peroxide). For H2O and
  H2O2, each has the same number of ___ atoms. For
  H2O, there is __ Oxygen (mass is___ g/mol), in
  H2O2, there are ___ atoms of Oxygen (mass is ___
  g/mol). The ratio of mass of Oxygen in Hydrogen
  Peroxide (_________) to mass of Oxygen in Water
  (_______) is 32/16 _____.
• Example
• Carbon reacts with oxygen to form two compounds.
  Compound A contains 2.41 g carbon for each
• 3.22 g oxygen. Compound B contains 6.71 g of
  Carbon and 17.9 g of oxygen What is the lowest
  whole-number mass ratio of carbon that combines
  with a given mass of oxygen?
• SOLUTION
  
• For each compound find the grams of carbon that
  combine per 1.00 g of oxygen.
• Compound A 2.41g C 0.748 g C
• 3.22 g O 1.00 g O
• Compound B 6.71 g C 0.375 g C
• 17.9 g O 1.00 g O
• The
  mass ratio of carbon per gram of oxygen in the
  compounds is 21.
• 
  0.748 g C (in
  compound A) 2
• 
  0.375 g C (in
  compound B) 1

2
1
whole
1
H2O
H2O2
1
16
H
2
32
H2O2
H2O
2
3

• The Structure of the Atom (pg. 72-75)
• - Dalton stated that atoms were indivisible, the
  following experiments showed that Dalton was
  __________.
• 1. Discovery of the Electron (1897) J.J. Thomson
  is credited with the discovery of the electron.
  The electron was found through the use of a
  cathode ray tube (also called a gas discharge
  tube).
• a. Thomson found that the cathode rays would
  deflect in the presence of __________ or
  __________ fields (See fig. 4, 5 pg. 72, 73).
  This experiment led Thomson to the calculation of
  the mass to charge _________ of the electron
  1.758.108 C/g (C is the coulomb which is the SI
  unit of electrical _________).
• b. Robert Millikan, found the _________ of an
  electron. To do this he levitated an oil drop,
  covered in ____________ , between charged plates.
  The value of the charge of an electron was found
  to be 1.6.10-19 Coulombs.
• c. From the combination of Thomsons and
  Millikans work, the mass of the electron was
  seen to be 1.6.10-19 C / 1.758.1011 C/kg
  ______________ kg (see page 73 of text).
• d. The charge of the electron was assigned a unit
  less value of -1 and the symbol of the electron
  was designated _________.

wrong
electric magnetic
ratio
charge
charge
electrons
9.11.10-31
e-1
4

• Homework
• How did Democritus and Aristotles viewpoints of
  the atom differ?
• What is an atom?
• 3a. What scientist is credited with the discovery
  of the electron?
• b. Describe the instrumentation was used to
  discover the electron.
• c. What else did this scientist discover about
  the electron?
• 4a. What scientist is credited with the discovery
  of the charge of the electron?
• b. Describe the instrumentation used to
  discover the charge of the electron.
• c. What about the electron was discovered from
  the combined works of the scientists in question
  3 and 4?
• d. What is the symbol of the electron?
• 5a. What are the positive and negative electrodes
  of a cathode-ray tube called?
• b. Of what is a cathode ray composed?
• c. Why are they called cathode rays?
• d. What can deflect cathode rays?
• 6. What scientist was the first to come up with
  an atomic model based upon experimental evidence?
• 7a. Whose work was Daltons atomic theory based
  upon?
• b. What did each of these scientists discover?
• c. What about Daltons theory is known to be
  untrue?
• d. Describe the Law of Definite Proportions.

5

• Atomic Structure Continued
• 2. Discovery of the Proton (not on test)
• a. E. Goldstein, in 1885, discovered the proton
  using a modified cathode ray tube (recall that
  the cathode is the - electrode.
• b. He placed holes in the cathode and found
  particles traveled from the cathode (the -
  electrode), through the holes in the cathode and
  struck the glass on the other side.
• c. These particles were called protons. Their
  charge was designated as 1 which equal but
  opposite in sign to the electrons -1 charge.
• d. Thomson found the mass to be about 2000 times
  larger than an electron .
• 3. Discovery of the Neutron (not on test)
• a. A third particle, the neutron was discovered
  by James Chadwick in 1930.
• b. A neutron has no charge and has a mass
  approximately equal to the protons mass.
• 4. Discovery of the Nucleus
• a. During the time period of 1912-1913, Lord
  Rutherford brought together a team of physicists
  including Niels Bohr, Hans Geiger, and Ernest
  Marsden. The development of the modern model of
  ___________ structure was determined from this
  teams experiments and Rutherfords guidance.
• b. Geiger and Marsden shot a stream of high speed
  alpha particles (an alpha particle is a
  positively charged Helium ion) from a radioactive
  source at a very thin piece of ______ foil. (See
  fig. 6 pg 74)
• c. They found that most of the particles
  _________straight through the gold foil. Some of
  the particles were ___________ at large angles.
  About 1 in 8000 of the particles ___________ back
  in the opposite direction. (Lord Rutherford said
  that this was like shooting a 15 inch shell at a
  tissue paper and having it bounce back and hit
  you).
• d. From the experiment Rutherford concluded that
  the atom was mostly _________ space. He also
  concluded that the atom had a very small core
  that was positively charged and contained most of
  the ________ of the atom. This core is now
  referred to as the ____________.

atomic
gold
passed
deflected
bounced
empty
mass
nucleus
6
empty

• e. Dimensions of the average atom which shows the
  atom is mostly________ space. The diameter of
  most atoms is between 100 and 500 pm (recall a pm
  is __________m). The nucleus of atoms ranges from
  0.0012 to 0.0075 pm and the radius of the
  electron is 0.00282 pm. Therefore, the nucleus
  occupies one trillionth of the volume of the
  atom. (Analogy imagine the nucleus is the size
  of a ping pong ball. The electron would then be
  roughly the size of a pea. The distance between
  the nucleus (ping pong ball) and the nearest
  electron (tennis ball) would be 1.35 km or nearly
  a mile).
• 5. Isotopes, Atomic and Mass Numbers
• Isotopes
• While working with Neon, J.J. Thomson found two
  types of neon atoms.
• These neon atoms behaved the same chemically, but
  differed in mass.
• Atoms which behave the same chemically but
  differed in mass are called _____________.
• Isotopes have the ______ number of protons but
  differ in the number of neutrons.
• Atomic Number
• In 1913, Henry Moseley discovered the atomic
  number.
• The atomic number (symbol Z) represents the
  number of __________ present in an atom of an
  element and is used to identify the element.
• Mass Number
• The ___________ number (symbol A) represents the
  total number of ___ and ___ (are called
  nucleons). A of protons of neutrons
• Since elements have a neutral charge, they
  contain the __________ number of protons
• and electrons.
• Example protium (hydrogen-1 or 1 1H), deuterium
  (hydrogen-2 or 21H) and tritium (hydrogen-3 or
  31H), all contain ___ proton but contain
  different numbers of neutrons (protium 0 no,
  deuterium 1 no, and tritium 2 no). Table 3 pg. 79

1.10-12
isotopes
same
protons
mass
p no
equal
1
7

• Practice problems 1-3 pg. 80
• Ions-An atom that has lost or gained
  ______________.
• How many protons, neutrons and electrons are
  contained in 23Na1 and 36Cl-1?
• 23Na1 11 p , 10 e- 12 no 36Cl-1 17 p , 18
  e- 19 no
• Atomic Mass Units
• 1. Recall that the mass of a proton is 1836
  times larger than an electron and is essentially
  ______ to the mass of a neutron.
• 2. Because the mass of protons and neutrons are
  so much larger than electrons, most of the mass
  of the atom is contained in the __________.
• 3. Because mass of an atom is extremely________,
  chemists discuss the mass of atoms using what are
  called atomic mass units (symbol u or amu). An
  atomic mass unit is based upon the mass of a
  nuclide of _____________ having a mass of exactly
  12 amu. A single atomic mass unit is ____ the
  mass of a carbon-12 nuclide (look at pg. 76 and
  notice that the masses of protons and neutrons
  are nearly 1 amu).
• Average Atomic Mass A weighted average of the
  atomic masses of the naturally occurring isotopes
  of an element.
• Determining Average Atomic Mass (see example
  pg. 81)
• Example 1 What is the atomic mass of hafnium
  if, out of every 100 atoms, 5 have a mass of
  176.00 amu, 19 have a mass of 177.00 amu, 27 have
  a mass of 178.00 amu, 14 have a mass of 179.00
  amu, and 35 have a mass of 180.00 amu?

electrons
equal
nucleus
small
1/12th
carbon-12
Avg mass (5 (176.00 amu) 19(177.00
amu)27(178.00 amu)14(179.00 amu)35(180.00
amu))
100
Avg mass 178.55 amu
8

• Example 2 What is the atomic mass of silicon if
  92.21 of its atoms have a mass of 27.977 amu,
  4.70 have a mass of 28.976 amu, and 3.09 have a
  mass of 29.974 amu?
• Homework
• Day 1 pg. 89 s 7-12, 19 and pg. 93 13 (also
  How many protons, neutrons and electrons are
  contained in 40Ca2 and 16O-2?) Bonus pg. 90 20

Avg mass (0.9221 (27.977 amu) 0.0470
(28.976amu) 0.0309 (29.974 amu))
Avg mass 25.7976 amu 1.3619 amu 0.92620 amu
Avg mass 28.09 amu
9

• Relative Mass to Numbers of Atoms
• The Mole If Avogadros (6.02.1023) of atoms
  of a compound are placed on a balance the balance
  will record the atomic mass in ________. For
  Example if 6.02.1023 atoms of carbon are placed
  on a balance the balance will read ________ g. A
  mole of a substance is merely a collection of
  particles like 12 make a dozen or 24 cans in a
  case or 144 make a gross.
• Molar Mass the mass of 1 mole of a substance is
  called the molar mass and has units of _______
• Example Problems
• Sample B pg. 84

grams
12.011
g/mol
?g Cu 3.50 mol Cu .
63.546 g Cu mol Cu
/

222 g Cu
/
Sample C pg. 85
?mol Al 11.9 g Al .
mol Al 26.981 g Al
0.441 mol Al
/
/
Sample D pg. 86
mol Ag 6.02.1023 atoms Ag
0.500 mol Ag
?mol Ag 3.01.1023 atoms Ag .
/
/
Sample E pg. 86
/
mol Cu . 6.02.1023 atoms
63.546 g Cu mol Cu
?g Cu 1.20.108 atoms Cu .
/
1.27.10-14 g Cu
/
/
63.546 g Cu 6.02.1023 atoms
/
1.27.10-14 g Cu
?g Cu 1.20.108 atoms Cu .
/
10
Homework Day 1 Practice 1-2 (top of page 85)
1-2 (bottom of pg. 85) 1-2 (pg. 86) 1-2 (pg.
87) Day 2 pg. 89-90 17 a,e 18a,c 21a,c
22c,e 23 a,d