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Chemistry Chapter 4
The Structure of
the Atoms
Top Ten
Table 3.1
Table
3.3
History of Chemistry
• 400 B.C. Greeks proposed 4 elements
– Earth
– Fire
– Water
– Air
• Next 2000 years—alchemy
• During this period discoveries were made
– Hg, S, Sb
– prepared acids
Controversial Greek Thinking!
Democritus (460-370 B.C):
-Matter is composed of “atomos” (now atoms)
-Atoms were homogeneous & indivisible
-Could not answer what holds atoms together
Aristotle (384 B.C.-322B.C.):
-Matter was continuous and indefinitely
divisible (did not believe in atoms)
-Matter made of earth, fire, air, & water
-Idea was accepted for nearly 2000 years!
Indivisible or Divisible?
Democritis vs. Aristotle
Late 1700’s
• Most chemists accepted element
definition
• Understood elements combined to
form compounds with various
properties
• Disagreed whether compounds are
always in the same ratio
What happened in 1790?
• Study of matter was revolutionized
by new emphasis on Quantitative
Analysis
• Aided by improved balances
• Measurements were actually
ACCURATE!!!
Robert Boyle
• Founder of Modern
Chemistry (1627-1691)
• Took the “Al” out of
Alchemy (although he
started as one)
• First scientist to
understand the
importance of careful
measurement
• Insisted science be based
on experiments
• Famous for P=1/V
Antoine Lavoisier
• Father of Modern
Chemistry (1743-1794)
• Recognized and named
hydrogen and oxygen
• Introduced the metric
system
• Wrote first list of
elements and revised
nomenclature
• Because of prominence in
pre-revolutionary
government, was beheaded
at the height of the
French revolution
John Dalton—Beginning of Modern
Atomic Theory
• Englishman from a Quaker
family (1766-1844)
• Revolutionized chemistry
by emphasizing that
atoms can have weights
and weights can be
measured (quantitative)
• Opened a school at age
12
• Color blind/researched
• Interested in botany
• Theory not accepted until
1905 Albert Einstein
paper
Dalton’s Atomic Theory (1808)
 Matter is composed of extremely
small particles called atoms
 Atoms are indivisible and
indestructible.
 Atoms of a given element are identical in size,
mass, and chemical properties.
 Atoms of specific element are different from those
of another element.
Different atoms combine in simple whole-number
ratios to form compounds.
 In chemical reactions, atoms are separated,
combined, or rearranged
Dalton vs. Today
Matter is composed of
extremely small particles
called atoms.
True
Atoms are indivisible and
indestructible.
Made up of smaller particles
(protons, neutrons, &
electrons)
except in nuclear chemistry.
 Atoms of a given elemet are  Atoms of a given element
identical in size, mass, and
have same p+ and e-, but may
chemical properties.
differ in # of neutrons
Atoms of a specific element
are different from those of
another element
True, how we identify them
Different atoms combine in
simple whole-number ratios to
form compounds
True, Law of Multiple
Proportions
In chemical reactions, atoms
are separated, combined, or
True
Law of Conservation of Mass
Mass is neither
created nor destroyed
during chemical or
physical reactions.
Total mass of reactants
=
Total mass of products
Antoine Lavoisier
Law of Multiple Proportions
• If two or more different compounds
are composed of the same two
elements, then the ratio is always
small whole numbers. (CO, CO2)
Figure 3.2: Representation of NO, NO2, and N2O.
What does an atom
look like?
(Sketch it on your
paper!)
This is The Modern Atomic Model
• Atom: The smallest particle of an element that
retains the properties of the element
• Only seen by STM (Scanning Tunneling
microscope)
Subatomic Particles
Particle
Charge
Mass (amu)
Location
Electron (e-)
J.J.Thomson 1897
Nobel Prize 1906
Robert Milllikan
(1910s)
-1
5.486x10-4 amu
9.1 x 10-28 g
1/1840 of H
Electron
cloud
Proton (p+)
Thomson/Goldstein1907
Rutherford 1920
+1
1.007 amu
1.673 x 10-24 g
Nucleus
0
1.009
1.675 x 10-24 g
Nucleus
Neutron (no)
Chadwick 1932
Nobel Prize 1935
Discovery of the Electron
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.
Figure 3.7: Schematic of a cathode ray
tube.
Some Modern
Cathode Ray Tubes
Mass of the Electron
1909 – Robert Millikan
determines the mass of
the electron.
The oil drop apparatus
Mass of the
electron is
9.1 x 10-28 g
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
 Electrons have so little mass that atoms must
contain other particles that account for most of
the mass
Thomson’s Atomic Model
Thomson believed that the electrons were like plums
embedded in a positively charged “pudding,” thus it was
called the “plum pudding” model.
Based on the following facts: (1) atoms contain small,
negatively charged particles called electrons and (2) the
atoms of the element behave as if they have no charge
at all
Ernest Rutherford
• 1871-1937
• Learned physics in JJ
Thomson’s lab
• Did much work with
alpha particles (+
charged part with
mass)
• Most famous for his
GOLD FOIL
EXPERIMENT
Figure 3.5: Rutherford’s
experiment.
Try it Yourself!
In the following pictures, there is a target hidden by
a cloud. To figure out the shape of the target, we
shot some beams into the cloud and recorded where
the beams came out. Can you figure out the shape of
the target?
The Answers
Target #1
Target #2
Figure 3.3: Plum Pudding model of an atom.
Figure 3.6:
Results of foil
experiment if
Plum Pudding
model had been
correct.
Figure 3.6: Actual results.
 Most of the particles passed right through
 A few particles were deflected
 VERY FEW
were greatly deflected
Rutherford’s
Findings
“Like howitzer shells bouncing off
of tissue paper!”
Conclusions:
 The nucleus is small
 The nucleus is dense
 The nucleus is positively charged
Disbelievers….
• Albert Einstein when to
his grave not totally
believing it
• According to classical
physics, the electron
would have collapsed into
the nucleus
• 1910-1930 began the
Quantum Physics
Revolution (the physics of
atomic and subatomic
particles)
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”
The Quark…
Oops…wrong Quark!
About Quarks…
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”
Figure 3.9:
A nuclear
atom viewed in
cross section.
Atomic Number
Atomic number (Z) of an element is the
number of protons in the nucleus of each atom
of that element.
Element
# of protons
Atomic # (Z)
6
6
Phosphorus
15
15
Gold
79
79
Carbon
Isotopes
Elements occur in
nature as mixtures
of isotopes.
Isotopes are atoms of
the same element that
differ in the number
of neutrons
Figure 3.10: Two isotopes of
sodium.
Mass Number
Mass number is the number of protons and
neutrons in the nucleus of an isotope.
Mass # = p+ + n0
Nuclide
p+
n0
e-
Mass #
Oxygen - 18
8
10
8
18
Arsenic - 75
33
42
33
75
Phosphorus - 31
15
16
15
31
Atomic Masses
Atomic mass is the average of all the naturally
isotopes of that element.
Carbon = 12.011
Isotope
Symbol
Composition of
the nucleus
% in nature
Carbon-12
12C
6 protons
6 neutrons
98.89%
Carbon-13
13C
6 protons
7 neutrons
1.11%
Carbon-14
14C
6 protons
8 neutrons
<0.01%
Isotopes…Again
(must be on the test)
Isotopes are atoms of the same element having
different masses due to varying numbers of neutrons.
Isotope
Protons
Electrons
Neutrons
Hydrogen–1
(protium)
1
1
0
Hydrogen-2
(deuterium)
1
1
1
Hydrogen-3
(tritium)
1
1
2
Nucleus
Chlorine Practice Problem
• Chlorine exists as 2 isotopes in nature.
Cl-35 (atomic mass 34.969 amu) has a
75.77% relative abundance. Cl-37 has
an atomic mass 36.966 amu.
1. What is the % abundance of the Cl37 isotope?
Chlorine Practice Problem
• Chlorine exists as 2 isotopes in nature.
Cl-35 (atomic mass 34.969 amu) has a
75.77% relative abundance. Cl-37 has
an atomic mass 36.966 amu
Calculate the atomic mass of Chlorine.
Chlorine Practice Problem
• Chlorine exists as 2 isotopes in nature.
Cl-35 (atomic mass 34.969 amu) has a
75.77% relative abundance. Cl-37 has
an atomic mass 36.966 amu.
How many times more massive is Cl-37
than Cl-35?
Radioactivity
• Radioactivity: a process in which some
substance spontaneously emit radiation
• Radiation: The rays and particles emitted by
the radioactive materials.
• Nuclear Reaction: A change in an atom’s
nucleus.
• Radioactive Decay: emitted radiation in a
spontaneous process
• Major Breakthrough: 1890’s.
• Only happens in radioactive atoms with unstable
nuclei
Types of Radiation
• Alpha Radiation
– Made up of alpha particles
– Deflected toward a negatively charged plate
• Beta Radiation
– Made up of beta particles
– Deflected toward a positively charged plate
• Gamma Radiation
– High E radiation that has no charge and mass
– Not deflected by electronic or magnetic
fields
Law of Definite (or Constant)
Composition
• The fact that a chemical compound
contains the same elements in
exactly the same proportions by
mass regardless of the size of the
sample or the source of the
compound.
What does this mean? (Law of
Definite Composition)
• 50.0 g sample of pure H2O decomposed into its
elements
– would find 5.6 g H and 44.4 g oxygen
– % mass would be:
mass H
total mass
= 5.60 g
50.0 g
x 100 = 11.2% H
mass 0
total mass
= 44.4 g
50.0 g
x 100 = 88.8% O
Atomic # and Atomic Mass
The Periodic Law
Chinese Periodic Table
Triangular Periodic Table
“Mayan”
Periodic
Table
Stowe Periodic Table
A Spiral Periodic Table
Modern Russian Table
The Year 1860….
• First International Congress of Chemists
– 60 to 70 of 113 elements had been
discovered
– Italian chemist Cannizzaro presented method
for measurement of atomic mass that all
could agree on.
Dimitri Mendeeleev
– Writing a book about the same time.
– Wanted to include new information of
atomic masses
– Wanted to find an arrangement for all
of the information on the 60-70
elements
Law of Mendeleev:
– Properties of the elements recur in
regular cycles (periodically) when the
elements are arranged in order of
increasing atomic mass.
Missing?
14
Si
28.09
??
50
Sn
118.71
Named missing
element
“Ekasilicon”
From base word
“eka” meanging
next in order
“Ekasilicon”
Predicted
Properties
Atomic Mass
72 amu
Density
5.5 g/cm3
Melting Point
825° C
Observed
Properties
“Ekasilicon”
Predicted
Properties
Observed
Properties
Atomic Mass
72 amu
72.61 amu
Density
5.5 g/cm3
5.32 g/cm3
Melting Point
825° C
938° C
“Ekasilicon”
Predicted
Properties
Observed
Properties
Oxide Formula
XO2
GeO2
Chloride Formula
XCl4
GeCl4
Mendeleev’s Periodic Table
Dmitri Mendeleev
Figure 3.11: The periodic table
Figure 3.11: The periodic table
Periodic Table with Group Names
Group or Family
Period
The Periodic Table
Group or
family
Period
Periodic Table with Group Names
Figure 3.12: Elements classified
as metals and nonmetals.
Properties of Metals
 Metals are good
conductors of heat and
electricity
 Metals are malleable
 Metals are ductile
 Metals have high tensile
strength
 Metals have luster
Figure 3.17: Spherical atoms packed closely together.
Metalloids:
• Mostly brittle solids
• Properties between metal and non-metal
(semi-conductors)
• With exception of Bismuth, found in
nature only as compound
• Once obtained as free metals, that are
stable in the presence of air
Properties of Nonmetals
Carbon, the graphite in “pencil lead” is a great
example of a nonmetallic element.
 Nonmetals are poor conductors of heat and
electricity
 Nonmetals tend to be brittle
 Many nonmetals are gases at room
temperature
Examples of Nonmetals
Sulfur, S, was
once known as
“brimstone”
Graphite is not the only
pure form of carbon, C.
Diamond is also carbon;
the color comes from
impurities caught within
the crystal structure
Microspheres
of phosphorus,
P, a reactive
nonmetal
Figure 3.14: Nitrogen gas contains N2 molecules.
Figure 3.13: A collection of argon
atoms.
Figure 3.14: Oxygen gas contains O2 molecules.
Table 3.5
Allotropes
• Different forms of a given element
• Different properties b/c different
arrangement of atoms
• EX: diamond, graphite,
Buckminsterfullerene (All Carbon!)
• Look in your book—p. 70
TYPES OF IONS (Remember an ion is an
atom or group of atoms that has a net + or
net – charge.
Cations
Anions
Positively charged ions
Smaller than the corresponding
atom (lost e’/closer together)
Negatively charged ions
Larger than the corresponding
atom (gained e’/spread apart
Table of Ion Sizes
Figure 3.11: The periodic table
Figure 3.19: The ions formed by selected members
of groups 1, 2, 3, 6, and 7.
Figure 3.20: Pure water does not conduct a
current.
Figure 3.20: Water containing dissolved salt
conducts a current.