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8/3/2019 Chemistry Notes Ch 3
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Chapter 3 1
Chapter 3
Atoms: The BuildingBlocks of Matter
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Chapter 3 2
Section 3-1
The Atom: FromPhilosophical Idea toScientific Theory
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Chapter 3 3
Foundations of Atomic Theory
In 400 B.C. Democritis called natures
basic particle the atom
Aristotle, however, did not believe inatoms, but thought all matter was
continuous.
His ideas were accepted for about 2000
years.
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Chapter 3 4
Foundations of Atomic Theory
In the late 1700s, during the
Enlightenment, science began to change
its ideas surrounding the structure ofmatter.
The modern definition of an element
came into general acceptance An element cannot be broken down into
simpler substances by ordinary means.
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Chapter 3 5
Foundations of Atomic Theory
In the late 1790s, chemists began the
quantitative study of chemical
reactions. Law of conservation of Mass
Mass is neither destroyed nor created
during ordinary chemical or physicalreactions.
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Chapter 3 6
Foundations of Atomic Theory
Law of Definite Proportions
The fact that a chemical compound
contains the same elements in exactly thesame proportions by mass regardless of
the size of the sample or source of the
compound. Example: NaCl is always NaCl
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Chapter 3 7
Foundations of Atomic Theory
Law of Multiple Proportions
If two or more different compounds are
composed of the same two elements, thenthe ratio of the masses of the secondelement combined with a certain mass ofthe first element is always a ratio of small
whole numbers. Example: CO and CO2
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Chapter 3 8
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Chapter 3 9
Daltons Atomic Theory
1. All matter is composed of extremely
small particles called atoms.
2. Atoms of a given element areidentical in size, mass, and other
properties; atoms of different
elements differ in size, mass, andother properties.
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Chapter 3 10
Daltons Atomic Theory
3. Atoms cannot be subdivided, created,or destroyed.
4. Atoms of different elements combinein simple whole-number ratios toform chemical compounds.
5. In chemical reactions, atoms arecombined, separated, or rearranged.
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Chapter 3 11
Daltons Atomic Theory
Therefore, chemical reactionsinvolve the
Combination Separation or
Rearrangement of atoms
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Chapter 3 12
Modern Atomic Theory
Not all of Daltons theories arecorrect.
We know that atoms are divisibleAtoms of the same element can have
different masses
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Chapter 3 13
Section 3-2
TheS
tructure of theAtom
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Chapter 3 14
The Structure of the Atom
Dalton was incorrect that atomswere indivisible.
Atom: the smallest particle of anelement that retains the chemical
properties of that element.
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Chapter 3 15
The Structure of the Atom
The atom contains three types ofsubatomic particles
1. Protons: Positively chargedparticles, in nucleus
2. Neutrons: Neutral particles, in
nucleus3. Electrons: Negatively charged
surrounding the nucleus.
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Chapter 3 16
Discovery of the Electron
J. J. Thomson - English physicist.1897
Made a piece of equipmentcalled a cathode ray tube.
It is a vacuum tube - all the airhas been pumped out.
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Chapter 3
Thomsons Experiment
Voltage source
+-
Vacuum tube
Metal Disks
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Chapter 3
Thomsons Experiment
Voltage source
+-
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Chapter 3
Thomsons Experiment
Voltage source
+-
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Chapter 3
Thomsons ExperimentThomsons Experiment
Voltage source
+-
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Chapter 3
Passing an electric current makes aPassing an electric current makes abeam appear to move from thebeam appear to move from the
negative to the positive endnegative to the positive end
Thomsons ExperimentThomsons Experiment
Voltage source
+-
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Chapter 3
Passing an electric current makes aPassing an electric current makes abeam appear to move from thebeam appear to move from the
negative to the positive endnegative to the positive end
Thomsons ExperimentThomsons Experiment
Voltage source
+-
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Chapter 3
Passing an electric current makes aPassing an electric current makes abeam appear to move from thebeam appear to move from the
negative to the positive endnegative to the positive end
Thomsons ExperimentThomsons Experiment
Voltage source
+-
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Chapter 3
Passing an electric current makes aPassing an electric current makes abeam appear to move from thebeam appear to move from the
negative to the positive endnegative to the positive end
Thomsons ExperimentThomsons Experiment
Voltage source
+-
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Chapter 3
Voltage source
Thomsons Experiment
By adding an electric field
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Chapter 3
Voltage source
Thomsons ExperimentThomsons Experiment
By adding an electric fieldBy adding an electric field
+
-
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Chapter 3
Voltage source
Thomsons ExperimentThomsons Experiment
By adding an electric fieldBy adding an electric field
+
-
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Chapter 3
Voltage source
Thomsons ExperimentThomsons Experiment
By adding an electric fieldBy adding an electric field
+
-
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Chapter 3
Voltage source
Thomsons ExperimentThomsons Experiment
By adding an electric fieldBy adding an electric field
+
-
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Chapter 3
Voltage source
Thomsons ExperimentThomsons Experiment
By adding an electric fieldBy adding an electric field
+
-
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Chapter 3
Voltage source
Thomsons ExperimentThomsons Experiment
By adding an electric field he foundBy adding an electric field he found
that the moving pieces were negativethat the moving pieces were negative
+
-
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Chapter 3 32
Discovery of the Electron
Thompson determined that thecharge/mass ratio of the negative
particle was constant. Concluded that all cathode rays
are composed of identical
negatively charged particlescalled electrons.
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Chapter 3 33
Discovery of the Electron
The electron has a very largecharge compared with its mass
In 1909, Millikan measured themass of the electron as9.109 x 10-31 kg
Also confirmed the negativecharge of the electron
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Chapter 3
Other particles
Proton - positively charged pieces
1840 times heavier than the
electron by E. Goldstein
Neutron - no charge but the same
mass as a proton by J. Chadwick Where are the pieces?
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Chapter 3
Rutherfords experiment
Ernest Rutherford -Englishphysicist. (1910)
Believed in the plum pudding modelof the atom
Wanted to see how big they are.
Used radioactivity.
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Chapter 3
Rutherfords experiment
Alpha particles - positively chargedpieces- helium atoms minus
electrons Shot them at gold foil which can be
made a few atoms thick.
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Chapter 3
Rutherfords experiment
When an alpha particle hits a
fluorescent screen, it glows.
Heres what it looked like (page
72)
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Chapter 3
Lead
blockUranium
Gold Foil
Fluorescent
Screen
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Chapter 3
He Expected
The alpha particles to pass throughwithout changing direction very much.
Because? the positive charges were thought tobe spread out evenly. Alone they were
not enough to stop the alpha particles.
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Chapter 3
What he expected
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Chapter 3
Because
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Chapter 3
He thought the mass was evenly
distributed in the atom
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Chapter 3
Since he thought the
mass was evenly
distributed in the atom
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Chapter 3
What he got
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Chapter 3
How he explained it
+
Atom is mostly empty.
Small dense,
positive pieceat center.
Alpha particles
are deflected by
it if they get close
enough.
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Chapter 3
+
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Chapter 3
Subatomic particles p.74
Electron
Proton
Neutron
Name Symbol Charge
Relative
mass
Actual
mass (g)
e-
p+
n0
-1
+1
0
1/1840
1
1
9.11 x 10-28
1.67 x 10-24
1.67 x 10-24
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Chapter 3 48
Composition of the Atomic Nucleus
The short-range proton-neutron,proton-proton, and neutron-
neutron forces that hold thenuclear particles together arereferred to as nuclear forces.
Colossians 1:17b In Christ, allthings hold together.
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Chapter 3 49
Section 3-3
Counting Atoms
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Chapter 3 50
Objectives
Explain what isotopes are
Define atomic number and mass
number, and describe how theyapply to isotopes
Given the identity of a nuclide,
determine its number of protons,neutrons and electrons
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Chapter 3 51
Objectives
Define mole in terms ofAvogadros number and define
molar mass Solve problems involving mass in
grams, amount in moles, and
number of atoms of an element.
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Chapter 3 52
Atomic Number
Atoms of the same element have thesame numbers of protons
Atoms of different elements havedifferent numbers of protons.
The atomic number of an element is
the number of protons in the nucleusof each atom of that element.
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Chapter 3 53
Atomic Number
Elements are arranged in theperiodic table in order by atomic
number. The atomic number identifies the
element.
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Chapter 3 54
Isotopes
Isotope: Atoms of the sameelement that have different
masses. The isotopes of a particular
element have the same number of
protons and electrons but differennumbers of neutrons.
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Chapter 3 55
Mass Number
Mass Number: the total numberof protons an neutrons in the
nucleus of an isotope
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Chapter 3 56
Designating Isotopes
Isotopes are identified byspecifying their mass number.
Two methods for identifyingisotopes:
Hyphen notation: Uranium-235
Nuclear symbol
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Chapter 3 57
Designating Isotopes
U23592AtomicNumber
Mass
Number
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Chapter 3 58
Designating Isotopes
See sample problem 3-1 on page77.
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Chapter 3 59
Relative Atomic Masses
1 amu or atomic mass unit isexactly 1/12 the mass of a carbon-
12 atom, or The atomic mass of any nuclide is
determined by comparison with
the carbon-12 atom.
kg10660540.127
v
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Chapter 3 60
Average Atomic Masses of Elements
Most elements occur as a mixtureof isotopes
Average atomic mass: theweighted average of the atomicmasses of the naturally occurring
isotopes of an element.
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Chapter 3 61
Average Atomic Masses of Elements
Suppose you have a boxcontaining two sizes of
marbles. If 25% have massesof 2.00 g, and 75% havemasses of 3.00 g, how is the
weighted average calculated?
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Chapter 3 62
Relating mass to numbers of atoms
The mole
A mole is the amount of
substance that contains asmany particles as there are inexactly 12 g of carbon-12.
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Chapter 3 63
Relating mass to numbers of atoms
Avogadros Number
The number of particles in
exactly 1 mole of a puresubstance
2310022.6 v
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Chapter 3 64
Relating mass to numbers of atoms
Molar Mass
The mass of one mole of a pure
substance is called the molarmass of that substance
Usually written in units of g/mol
For elements, molar mass can befound in the periodic table
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Chapter 3 65
Gram/Mole Conversions
The decimal number on the periodictable is also the mass of 1 mole ofthose atoms in grams.
12.01 grams of C has the same number ofpieces as 1.008 grams of H and 55.85grams of iron.
We can write this as12.01 g C = 1 mole C
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Chapter 3 66
Gram/Mole Conversions
The decimal number on the periodictable is also the mass of 1 mole ofthose atoms in grams.
12.01 grams of C has the same number ofpieces as 1.008 grams of H and 55.85grams of iron.
We can write this as12.01 g C = 1 mole C
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Chapter 3 67
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Chapter 3 68
Gram/Mole Conversions
Work through sample problems on p.82-85 together
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