Chapter 3 The Building Blocks of Matter

1
Chapter 3 The Building Blocks of Matter,
Atomic Structure, and Nuclear Chemistry Note
Letters correspond to answers on assignment 1
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Ancient Thougths
3
The History of the Atom

• Time Line
• A) Democritus 400 B.C. Philosopher atom
• B) Indivisible cannot be broken down into
• smaller parts.
• C) Aristotle 384 322 B.C. Didnt agree with
  Dem.
• Mid to late 1700s ? better equipment ? laws
• 1700s late ? John Dalton Daltons Theory
• 1897 ? Thomson
• 1911 ? Rutherford
• 1913 ? Neils Bohr

4
Mid to Late 1700sQuantitative Analysis evolved

• Better equipment ?
• measuring masses?
• 3 important laws

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3 Laws

• D)
• Law of conservation of mass Mass is neither
  created nor destroyed ,only rearranged.
• Law of definite proportions A compound contains
  the same elements in exactly the same proportions
  by mass, regardless of the sample size. Pg 69
  Text
• Law of multiple proportions 2 or more different
  compounds can be composed of the same elements,
  but will have different whole number ratios of
  the atoms. Pg 69 Text
• Mrs. X. Story (class discussion)

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John Dalton E) G)

• Modern Atomic Theory
• All matter is made of atoms
• Atoms of an element have a characteristic
  average mass which is unique to that element.
• Atoms cannot be subdivided, created, or
  destroyed in ordinary chemical reactions.
  However, these changes CAN occur in nuclear
  reactions! The atom is divisible
• All matter is composed of atoms
• Atoms of any one element differ in properties
  from atoms of another element

• Daltons Theory
• Matter is made of small particles atoms
• Atoms of the same element are alike and atoms of
  different elements are different in terms o
  properties.
• Atoms are indivisible
• Atoms combine in small whole number ratios to
  form compounds
• Atoms are combined, separated, and rearranged in
  chemical reactions.

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Modern Theory Summary

• F)
• 1) All matter is composed of atoms
• 2) Atoms of any one element differ in properties
  from atoms of another element .

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John Dalton
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Atomic Particles H)-I) Atom the smallest part
of an element with all of the properties of that
element
Particle Charge Relative Mass Location
Electron -1 0 Electron cloud
Proton 1 1 Nucleus
Neutron 0 1 Nucleus
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Discovery of the Electron J)
In 1897, J.J. Thomson used a cathode ray tube to
deduce the presence of a negatively charged
particle.
Cathode ray tubes pass electricity through a gas
that is contained at a very low pressure.
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Conclusions from the Study of the Electron

• Cathode rays have identical properties
  regardless of the element used to produce them.
  All elements must contain identically charged
  electrons.
• Atoms are neutral, so there must be positive
  particles in the atom to balance the negative
  charge of the electrons indirect evidence
• Electrons have so little mass that atoms must
  contain other particles that account for most of
  the mass

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Thomsons Atomic Model L)
Thomson believed that the electrons were like
plums embedded in a positively charged pudding,
thus it was called the plum pudding model. He
knew the atom to be neutral, but could never
prove the positive protons.
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The Electron
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American PhysicistRobert Millikan

• K)
• Millikan proved the charge on the electron to be
  negative with his famous oil drop experiment.

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Rutherfords Gold Foil Experiment

• Alpha (radioactive) particles are helium nuclei
• Particles were fired at a thin sheet of gold
  foil
• Particle hits on the detecting screen (film) are
  recorded

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Rutherford
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Rutherfords Conclusions M)

• Most of the particles passed right through
• A few particles were deflected
• VERY FEW were greatly deflected

Like howitzer shells bouncing off of tissue
paper!
Conclusions

• The nucleus is small
• The nucleus is dense
• The nucleus is positively charged

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The Atomic Scale

• Most of the mass of the atom is in the nucleus
  (protons and neutrons)
• Electrons are found outside of the nucleus (the
  electron cloud)
• Most of the volume of the atom is empty space

q is a particle called a quark
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The Neutron
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About Quarks extra info
Protons and neutrons are NOT fundamental
particles.
Protons are made of two up quarks and one
down quark.
Neutrons are made of one up quark and two
down quarks.
Quarks are held together by gluons
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Forces within an atom N)

• Electromagnetic (electrostatic) forces-
• Attractive forces holds the atom together.
  Opposite charges attract.
• Repulsive forces exist in the nucleus
  between protons exist in the electron cloud
  between electrons. Like forces repel.
• Strong force Over powers the repulsive
  electromagnetic force
• Gravity the effect on a single atom is still
  not fully understood.
• Weak force associated with radioactive decay

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Atomic Number
Atomic number of an element is the number of
protons in the nucleus of each atom of that
element. Identifies the element.
Element of Protons Atomic
Carbon 6 6
Phosphorus 15 15
Gold 79 79
Neutral atoms Protons and electrons are equal
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Atomic Masses
Atomic mass is the average of all the naturally
occurring isotopes of that element.
Uranium 238.028..
Isotope Symbol Atomic mass in amus (atomic mass units) in nature
Uranium-234 U-234 234.040945 .0054
Uranium-235 U-235 235.043922 .7204
Uranium-238 U-238 238.050784 99.2742
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Isotopes
Isotopes are atoms of the same element having
different masses due to varying numbers of
neutrons.
Isotope Protons Electrons Neutrons Mass (Nucleus)
Hydrogen1 (protium) 1 1 0 1
Hydrogen-2 (deuterium) 1 1 1 2
Hydrogen-3 (tritium) 1 1 2 3
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• 2 ways to write isotopes
• Nuclear Notation

Mass number (p no)
Element symbol
Atomic number (number of p)
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2. Hyphen - Notation

• U - 235

Mass number (p no)
Element symbol
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Mass Number
NOT ON THE PERIODIC TABLE Mass number is the sum
of protons and neutrons in the nucleus of a given
isotope.
Mass p n0
Nuclide (radioactive nucleus) p n0 e- Mass
Oxygen - 10
- 33 42
- 31 15
8
8
18
18
Arsenic
75
33
75
Phosphorus
15
31
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Nuclide worksheets (I) and (II)
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Types of Radioactive Decay

• Alpha production (a) helium nucleus
• Beta production (b ) sometimes called
• b - negative

4
He
2
0
e
-1

• Positron production sometimes called b

0
e
1
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Marie Curie
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Alpha Radiation
Limited to VERY large nuclei.
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Beta RadiationBeta (-)
Converts a neutron into a proton.
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Other Types of Radioactive Decay Extra info.

• gamma ray production (g)
• electron capture (inner-orbital electron is
  captured by the nucleus)

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Types of Radiation
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Nuclear EquationsTransmutation
Alpha
Beta
Beta

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NuclearStability
Decay will occur in such a way as to return a
nucleus to the band (line) of stability.
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Half-life Concept
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Sample Half-Lives
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A radioactive nucleus reaches a stable state by a
series of steps
A Decay Series
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Half life calculations

• (½) n
• n of ½ life's that have occurred
• Mass (g) x (½)n mass remaining
• Sample Calculation
• Fluorine -21 has a half-life of approx. 5
  seconds. What fraction of the nuclei would remain
  after 1 minute?
• If you began with 42 grams of fluorine, how
  many grams of fluorine would remain?

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Workspace
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Deflection of Decay Particles
attract
Opposite charges_________ each other.
repel
Like charges_________ each other.
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Nuclear Fission and Fusion

• Fusion Combining two light nuclei to form a
  heavier, more stable nucleus.
• Fission Splitting a heavy nucleus into two
  nuclei with smaller mass numbers.

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Fission
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Fission Processes
A self-sustaining fission process is called a
chain reaction.
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A Fission Reactor
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Fusion
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QuestionIs it possible to relate amus to grams,
numbers of atoms and the mole? YES!!!!!

• C 12
• C -12 has been assigned 12 a.m.us
• (atomic mass units)
• This is the standard that was arbitrarily chosen.
• \

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The Mole
1 dozen
12
1 gross
144
1 ream
500
1 mole
6.022 x 1023 parts
There are exactly 12 grams of carbon-12 in one
mole of carbon-12. 6.022 x 10 23 C-12 atoms
1mol C-12
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Avogadros Number
6.022 x 1023 is called Avogadros Number in
honor of the Italian chemist Amadeo Avogadro
(1776-1855).
I didnt discover it. Its just named after me!
Amadeo Avogadro
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Answer

• Multiply
• amus from periodic table (pick any element)
• mass of p (1.67 x 10 -24 grams)
• Avogadros number (6.022 x 10 23 atoms/mol)
• Ex
• 12.0107 amus X 1.67 x 10 -24 grams X 6.022 x
  1023 atoms/mol

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Molar mass Summary
to Question

• Molar Mass mass in grams of one mole of any
  pure substance
• Units g/mol
• Note The Modern text will round the molar mass
  to 100th place.
• Molar mass for atoms Na, K, Cu, N, Br, O
• Molar mass for 1 molecule of the following
  compounds H2O CO CO2
• CaCl2
  Ca(C2H3O2)2

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Conversion Roadway!

• molar mass (g/mol)
  
  Avogadros
• from periodic table
  1
  6.022 x 10 23
• Mass (g) MOL
  Parts
• 
  (atoms),
• 
  
  (molecules)

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Calculations Converting moles to grams
How many grams of lithium are in 3.50 moles of
lithium?
3.50 mol Li
6.94 g Li
?g Li
g Li
24.3
1 mol Li
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Calculations Converting grams to moles
How many moles of lithium are in 18.2 grams of
lithium?
18.2 g Li
1 mol Li
?mol Li
mol Li
2.62
6.94 g Li
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Calculations converting moles to atoms
How many atoms of lithium are in 3.50 moles of
lithium?
?atoms Li
3.50 mol Li
6.022 x 1023 atoms Li
atoms Li
2.11 x 1024
1 mol Li
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Calculations Converting grams to atoms
How many atoms of lithium are in 18.2 g of
lithium?
? Atoms Li
18.2 g Li
1 mol Li
6.022 x 1023 atoms Li
6.94 g Li
1 mol Li
atoms Li
1.58 x 1024
(18.2)(6.022 x 1023)/6.94