Transcript Chapter 1: Matter and Measurement

A Call For Volunteers
• I have been approached by the special needs
department here at the university requesting
a student interested in helping another
student in class by taking notes.
• Anyone interested in this should see me
after class to make arrangements.
Slide 1 of 25
Chemistry 140 Fall 2002 Dutton
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What about a supersaturated solution?
• Consider a supersaturated salt solution.
• Because it is a mixture it is chemically
heterogeneous (salt and water)
• Because there is dissolved and undissolved
salt in the beaker, there are two phases of
the salt making it physically heterogeneous
(two different phases).
Slide 2 of 25
Chemistry 140 Fall 2002 Dutton
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General Chemistry
Principles and Modern Applications
Petrucci • Harwood • Herring
8th Edition
Chapter 2: Atoms and the Atomic Theory
Slide 3 of 25
Chemistry 140 Fall 2002 Dutton
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Contents
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•
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Early chemical discoveries
Electrons and the Nuclear Atom
Chemical Elements
Atomic Masses
The Mole (save this for Friday)
Slide 4 of 25
Chemistry 140 Fall 2002 Dutton
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Early Discoveries
Antoine Lavoisier
Law of conservation of mass
Before reaction = 0.455 g Mg + 2.315 g O2 = 2.770 g
After reaction = ? g MgO + 2.015 g O2 = 2.770 g
0.755 g MgO
Proust 1799
Slide 5 of 25
Law of constant composition
Chemistry 140 Fall 2002 Dutton
Prentice-Hall © 2002
Early Discoveries
Lavoisier 1774
Law of conservation of mass
Before reaction = 0.455 g Mg + 2.315 g O2 = 2.770 g
After reaction = ? g MgO + 2.015 g O2 = 2.770 g
0.755 g MgO
Proust 1799
Law of constant composition
Sample A
Composition
10.000 g
Slide 6 of 25
Sample B
27.000 g
1.119 g H
% H = 11.19
3.021 g H
8.881 g O
% O = 88.81
23.979 g O
Chemistry 140 Fall 2002 Dutton
Prentice-Hall © 2002
Dalton’s Atomic Theory (1803-1808)
 Each element is composed of small
particles called atoms.
 Atoms are neither created nor destroyed
in chemical reactions.
 All atoms of a given element are identical.
 Compounds are formed when atoms of
more than one element combine.
Slide 7 of 25
Chemistry 140 Fall 2002 Dutton
John Dalton
(1766-1844)
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Consequences of Dalton’s theory
 Law of Definite Proportions: combinations of elements are
in ratios of small whole numbers.
 In forming carbon monoxide, 1.33 g
of oxygen combines with 1.0 g of
carbon.
 In the formation of carbon dioxide
2.66 g of oxygen combines with 1.0 g
of carbon.
Slide 8 of 25
Chemistry 140 Fall 2002 Dutton
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Behavior of charges
Like charges repel each other
Opposite charges attract
Oppositely charged
particles are deflected
in opposite directions
by a magnetic field.
Slide 9 of 25
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Cathode ray tube (Discovery of Electrons)
Slide 10 of 25
Chemistry 140 Fall 2002 Dutton
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Properties of cathode rays
Electric Field
Magnetic Field
Electron m/e = -5.6857 x 10-9 g coulomb-1
Slide 11 of 25
Chemistry 140 Fall 2002 Dutton
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Charge on the electron
 From 1906-1914 Robert Millikan showed ionized oil drops
can be balanced against the pull of gravity by an electric field.
The charge is an integral multiple of the electronic charge, e.
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Chemistry 140 Fall 2002 Dutton
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Radioactivity
Radioactivity is the spontaneous emission of radiation
from a substance.
 X-rays and g-rays are high-energy light.
 a-particles are a stream of helium nuclei, He2+.
 b-particles are a stream of high speed electrons
that originate in the nucleus.
Slide 13 of 25
Chemistry 140 Fall 2002 Dutton
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The nuclear atom
Geiger and
Rutherford
1909
To study
Thompson’s model
of the atom
1. Majority of α-particles penetrated undeflected.
2. Some α-particles experienced slight deflections.
3. A few (1/20000) suffered serious deflections.
4. A few didn’t penetrate but deflected back from where they came.
Slide 14 of 25
Chemistry 140 Fall 2002 Dutton
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The a-particle experiment
 Most of the mass and all of the
positive charge is concentrated in a
small region called the nucleus .
What actually
happened
What was expected
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 There are as many electrons outside
the nucleus as there are units of
positive charge on the nucleus
Chemistry 140 Fall 2002 Dutton
Prentice-Hall © 2002
The nuclear atom
Rutherford
1. Most of the mass and all
of the positive charge are protons 1919
centered in a very small
region called the nucleus.
2. The magnitude of the
positive charge is
different for different
atoms and is ½ of the
atomic weight.
3. The atom as a whole is
electrically neutral.
Protons = electrons.
Slide 16 of 25
James Chadwick
neutrons 1932
Chemistry 140 Fall 2002 Dutton
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Nuclear Structure
Atomic Diameter 10-8 cm
Nuclear diameter 10-13 cm
1Å
Particle
Electron
Proton
Neutron
Slide 17 of 25
Mass
kg (SI)
9.109 x 10-31
1.673 x 10-27
1.675 x 10-27
amu
0.000548
1.00073
1.00087
Chemistry 140 Fall 2002 Dutton
Charge
Coulombs (SI)
–1.602 x 10-19
+1.602 x 10-19
0
(e)
–1
+1
0
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Scale of Atoms
The heaviest atom has a mass of only 4.8 x 10-22 g
and a diameter of only 5 x 10-10 m.
Useful units:
 1 amu (atomic mass unit) = 1.66054 x 10-24 kg
 1 pm (picometer) = 1 x 10-12 m
 1 Å (Angstrom) = 1 x 10-10 m = 100 pm = 1 x 10-8 cm
Biggest atom is 240 amu and is 50 Å across.
Typical C-C bond length 154 pm (1.54 Å)
Molecular models are 1 Å /inch or about 0.4 Å /cm
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Isotopes, atomic numbers and mass numbers
To represent a particular atom we use the symbolism:
A= mass number
Slide 19 of 25
Z = atomic number
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Measuring atomic masses
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Chemistry 140 Fall 2002 Dutton
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