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Slide 1 ___________________________________ 5 Early Atomic Theory and Structure
___________________________________ ___________________________________ ___________________________________ ___________________________________ Lightning occurs when electrons
move to neutralize charge difference
between the storm clouds and Earth.
___________________________________ Foundations of College Chemistry, 14th Ed.
Morris Hein and Susan Arena
___________________________________ Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ Chapter Outline
2 5.1
Dalton’s Model of the Atom
5.2
Electric Charge
___________________________________ ___________________________________ A. Discovery of Ions
5.3
Subatomic Parts of the Atom
5.4
The Nuclear Atom
5.5
Isotopes of the Elements
5.6
Atomic Mass
3 ___________________________________ ___________________________________ ___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ ___________________________________ Early Theories on the Structure of Matter
___________________________________ Early models of the atom were developed by the Greeks.
Empedocles proposed matter was composed of
four basic elements: earth, air , water and fire.
___________________________________ Democritus proposed matter was composed of small,
indivisible particles he called atoms.
___________________________________ Atoms could combine in different ways,
giving rise to the diversity of compounds we observe.
___________________________________ ___________________________________ Aristotle, an influential philosopher,
supported Empedocles’ theory, so atomic theory was not
fully accepted until 2000 years later.
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ Slide 4 ___________________________________ Dalton’s Model of the Atom
___________________________________ Dalton’s theory of atoms,
proposed in the early 1800s, states:
1. Elements are composed of small, indivisible particles
called atoms.
2. Atoms of the same element are identical in mass and size.
___________________________________ ___________________________________ 3. Atoms of different elements differ in their mass and size.
4. Compounds are formed by combining two or more atoms
of different elements.
5. Atoms combine to form compounds in simple whole
number ratios.
___________________________________ 6. Atoms of two elements may combine in different ratios,
leading to formation of different compounds.
___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 5 ___________________________________ ___________________________________ Dalton’s Model of the Atom
___________________________________ ___________________________________ H2 O
___________________________________ H2 O 2
a. Atoms are individual particles which are different
for each element.
b./c. Atoms combine in fixed ratios to form compounds.
Two elements can combine in varying ratios
to give different compounds.
___________________________________ ___________________________________ Most of Dalton’s theory remains valid today.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 6 ___________________________________ ___________________________________ Dalton’s Model of the Atom
___________________________________ Revisions to Dalton’s Theory
___________________________________ 1. Elements can be decomposed under certain conditions.
___________________________________ 2. Not all atoms of the same element have identical mass.
These are called isotopes.
___________________________________ ___________________________________ 3. Atoms are not indivisible.
Atoms are composed of subatomic particles.
___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ Electric Charge
7 ___________________________________ Properties of Electric Charge
1. Charge may be either positive or negative.
2. Opposite charges (positive and negative) attract
while like charges (i.e. negative and negative) repel.
___________________________________ 3. Charge may be transferred from one object to another,
by contact or induction.
___________________________________ 4. The force of attraction between charges (F) is related to
the distance between charges by:
___________________________________ F=
kq1q2
___________________________________ r2
where q1 and q2 are the charges,
r is the distance between charges, and k is a constant.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 8 ___________________________________ ___________________________________ Discovery of Ions
Michael Faraday: English scientist who discovered
electrolytes (compounds that conduct electricity
when dissolved in water).
___________________________________ ___________________________________ Faraday also discovered that some compounds
decompose in water into their elements.
___________________________________ These elements were attracted to either negatively
or positively charged electrodes in the solution,
meaning they were no longer neutral.
___________________________________ These charged elements are called ions.
___________________________________ A light bulb glows when ions are present
in a saltwater solution when current is
passed through it.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ ___________________________________ The Nature of Ions
9 ___________________________________ Arrhenius extended Faraday’s work.
He proposed ions are atoms (or groups of atoms)
that carry a positive or negative charge.
Ex. NaCl in water dissociates into two ions,
The
Na+
and
___________________________________ Cl–.
___________________________________ Na+
(cation) produced is attracted to the negatively
charged electrode (cathode).
–
The Cl (anion) produced is attracted to the positively
charged electrode (anode).
___________________________________ Based on Faraday’s and Arrhenius’ work, Stoney proposed
the electron was a fundamental unit of electricity
associated with atoms. J. J. Thomson later
experimentally confirmed the existence of electrons.
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ ___________________________________ Slide 10 ___________________________________ Subatomic Parts of the Atom
___________________________________ A single atom is tiny (diameter of 0.1 to 0.5 nm).
Because atoms are so small, determining the presence
of subatomic particles was very difficult.
___________________________________ New instruments in the early 1900s permitted
detection of these particles.
___________________________________ ___________________________________ ___________________________________ ___________________________________ A scanning tunneling microscope (STM) image shows an array of Cu atoms.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 11 ___________________________________ Subatomic Parts of the Atom
___________________________________ A Crooks tube permits generation of cathode rays,
which are streams of electrons.
___________________________________ ___________________________________ ___________________________________ ___________________________________ A Crooks (cathode) ray tube. The stream of electrons passes between the electrodes.
The electron beam is deflected by both electric
and magnetic fields, indicating it has charge.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 12 ___________________________________ ___________________________________ Electrons and Protons
___________________________________ Electrons (e–):
A particle with negative electrical charge
(assigned a relative charge of –1).
Electrons have a very small mass
(9.110 x 10–28 g) and size (<10–12 cm).
___________________________________ Protons (p):
___________________________________ ___________________________________ A particle with positive electrical charge
(assigned a relative charge of +1).
Protons have a much larger mass
(~1837 times the mass of an electron).
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ ___________________________________ Slide 13 ___________________________________ The Effect of Subatomic Particles
___________________________________ Thomson’s work demonstrated the atom is composed
of smaller, charged particles.
Dalton’s theory of the atom then had to be revised.
___________________________________ Thomson’s Model of the Atom
___________________________________ Electrons are negatively charged particles which are
embedded in a positively charged atomic sphere.
___________________________________ Electrons
+ charged
sphere
___________________________________ Thomson’s “plum pudding”
model of the atom.
___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 14 ___________________________________ The Effect of Subatomic Particles
___________________________________ Atoms can become ions by gaining or losing
electrons from this sphere.
___________________________________ ___________________________________ Electrons are lost from atoms to give cations.
___________________________________ ___________________________________ ___________________________________ Electrons are gained from atoms to give anions.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 15 ___________________________________ Neutrons
___________________________________ The last subatomic particle was discovered
by Chadwick in 1932.
___________________________________ Neutrons (n)
___________________________________ A particle with no electrical charge.
Neutrons have a mass similar to that of a proton.
___________________________________ ___________________________________ ___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 16 ___________________________________ Summary of Subatomic Particles
___________________________________ Atoms are composed of three smaller, subatomic
particles: electrons, protons and neutrons.
___________________________________ ___________________________________ ___________________________________ Chemical properties of atoms can be described
based on the electrons, protons and neutrons.
___________________________________ Though other subatomic particles are now known,
the theories of atomic structure are based
only on these 3 subatomic particles.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 17 ___________________________________ ___________________________________ Nuclear Model of the Atom
In 1911, Ernest Rutherford established the nuclear model
of the atom by bombarding gold atoms with α particles.
___________________________________ ___________________________________ ___________________________________ ___________________________________ Most of the particles passed through the gold foil,
but some were deflected and some even bounced back!
___________________________________ This suggested the gold atoms must have a densely,
positively charged nucleus to affect the path of an
α particle (a positively charged He atom).
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 18 ___________________________________ ___________________________________ Nuclear Model of the Atom
___________________________________ Because most of the particles were not deflected,
this suggested most of the atom is empty space.
___________________________________ ___________________________________ ___________________________________ Protons and neutrons are located in the nucleus.
Electrons are dispersed throughout the remainder
of the atom (mainly open space).
Neutral atoms contain the same number of protons
and neutrons to maintain charge balance.
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ ___________________________________ Slide 19 ___________________________________ Atomic Number
___________________________________ Atomic Number: Number of protons in the
nucleus of an atom.
___________________________________ The atomic number determines the identity of the atom.
___________________________________ Atomic numbers for every element are above the
element’s symbol in the periodic table.
___________________________________ 27
___________________________________ Atomic Number
Co
___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 20 ___________________________________ Isotopes of the Elements
___________________________________ After discovery of the nuclear model of the atom,
the mass of almost all atoms was found to be larger than
expected, based on the number of protons and electrons.
This led to the discovery of neutrons.
___________________________________ Though all atoms of the same element have the same
number of protons, atoms of the same element may have
different numbers of neutrons.
___________________________________ ___________________________________ ___________________________________ Isotopes: atoms of an element with the same atomic
number but different numbers of neutrons.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 21 ___________________________________ ___________________________________ Isotopes of the Elements
Example: Isotopes of Hydrogen
Protium
Deuterium
___________________________________ Tritium
___________________________________ ___________________________________ 1 proton
0 neutrons
1 proton
1 neutron
1 proton
2 neutrons
___________________________________ Standard Isotopic Notation
Mass Number
A
Atomic Number
Z
E
___________________________________ Element Symbol
Mass number: Total number of protons and neutrons
for an element.
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ Slide ___________________________________ Isotopes of the Elements
22 ___________________________________ ___________________________________ ___________________________________ Practice:
How many protons, neutrons, and electrons are found
in each of the following isotopes?
___________________________________ 64
Cu
29
___________________________________ Atomic Number: 29 protons (therefore 29 electrons)
# Neutrons = Mass Number – Atomic Number
64 – 29 = 35 neutrons
___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ Let’s Practice!
23 ___________________________________ Which isotope corresponds to an element with
24 protons and 28 neutrons?
___________________________________ a.
28
52
Cr
Solution:
___________________________________ b.
52
24
Cr
c.
52
28
Ni
# protons = Atomic Number = 24
Element: Cr
___________________________________ Mass Number = protons + neutrons
= 24 + 28 = 52
___________________________________ d. 128 Te
52
e.
24
52
Cr
___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide ___________________________________ Atomic Mass
24 ___________________________________ Because the mass of a single atom is so small,
it is inconvenient to use this as a mass unit.
___________________________________ Instead, relative atomic mass units (amu) are used.
___________________________________ 12
Using carbon-12, 6 C , as a standard, 1 atomic mass unit
is equal to 1/12th the mass of a carbon-12 atom.
___________________________________ 1 amu = 1.6606 x 10-24 g
___________________________________ All periodic tables use atomic masses based on
the carbon-12 isotope.
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ Slide 25 ___________________________________ Atomic Mass and Isotope Distribution
___________________________________ Since most elements are a mixture of isotopes,
the atomic mass for an element is the weighted average
of all naturally occurring isotopes of the element.
Example:
The atomic mass of Cu is 63.546 amu.
Cu exists as 2 major isotopes, Cu-63 and Cu-65.
___________________________________ Cu-63 is more abundant,
as the atomic mass is very close to 63 amu.
___________________________________ Calculating average atomic mass:
___________________________________ Sum of the atomic mass of each isotope
multiplied by its % abundance.
___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 26 ___________________________________ ___________________________________ Atomic Mass and Isotope Distribution
___________________________________ ___________________________________ Average atomic mass of Cu:
___________________________________ (62.9298) x (0.6909) + (64.9278) x (0.3091) = 63.55 amu
Atomic Mass % Abundance
___________________________________ Atomic Mass % Abundance
___________________________________ Measuring Cu isotope abundances
by using mass spectrometry.
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 27 ___________________________________ ___________________________________ Atomic Mass Practice
___________________________________ Silver exists as two isotopes with atomic masses of
106.9041 and 108.9047 amu.
Determine the average atomic mass for silver if the
% abundance for each isotope is 51.82 and
48.18%, respectively.
___________________________________ ___________________________________ ___________________________________ Average atomic mass of Ag:
(106.9041) x (.5182) + (108.9047) x (0.4818) = 107.8680 amu
___________________________________ Atomic Mass % Abundance Atomic Mass % Abundance
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________ Slide 28 ___________________________________ Let’s Practice!
Chlorine exists as two isotopes, Cl-37 (36.96590 amu)
and Cl-35. If the percent abundance of each isotope is
24.47 % and 75.53 %, what is the atomic mass of
Cl-35 if the average atomic mass is 35.46 amu?
___________________________________ a. 36.95690
d. 34.96885
b. 36.57823
e. 33.56438
c. 35.64544
Solution:
___________________________________ ___________________________________ ___________________________________ Solve for a:
___________________________________ (36.96590) x (.2447) + (a) x (0.7553) = 35.46 amu
9.046 + (a) x (0.7553) = 35.46 amu
(a) x (0.7553) = 26.41 amu
© 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 29 ___________________________________ a = 34.97 amu
___________________________________ Learning Objectives
___________________________________ 5.1 Dalton’s Model of the Atom
Describe Dalton’s model of the atom and compare it to the
earlier concepts of matter.
___________________________________ 5.2 Electric Charge
___________________________________ Use Coulomb’s Law to calculate the force between particles
and distinguish between a cation and anion.
___________________________________ 5.3 Subatomic Parts of the Atom
___________________________________ Describe the three basic subatomic particles and
how they changed Dalton’s model of the atom.
___________________________________ © 2014 John Wiley & Sons, Inc. All rights reserved.
Slide 30 ___________________________________ Learning Objectives
___________________________________ 5.4 The Nuclear Atom
___________________________________ Explain how the nuclear model of the atom differs
from the Dalton and Thomson models.
___________________________________ 5.5 Isotopes of the Elements
Define the terms atomic number, mass number
and isotope.
___________________________________ 5.6 Atomic Mass
___________________________________ Define the relationship between the atomic mass of an
element and the masses of its isotopes.
© 2014 John Wiley & Sons, Inc. All rights reserved.
___________________________________