Transcript Chapter 4

Chapter 4
Chemical Foundations:
Elements, Atoms, and
Ions
Chapter 4
Table of Contents
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
4.11
The Elements
Symbols for the Elements
Dalton’s Atomic Theory
Formulas of Compounds
The Structure of the Atom
Introduction to the Modern Concept of Atomic
Structure
Isotopes
Introduction to the Periodic Table
Natural States of the Elements
Ions
Compounds That Contain Ions
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Section 4.5
The Structure of the Atom
•
•
•
Substances that cannot be broken down by
simple chemical means
115 known: 88 found in nature, others are man
made.
Just as you had to learn the 26 letters of the
alphabet before you learned to read and write,
you need to learn the names and symbols of
the chemical elements before you can read and
write chemistry.
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Section 4.5
The Structure of the Atom
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Section 4.5
The Structure of the Atom
How the Term Element is Used
•
•
•
•
Could mean a single atom of that element (Ar
or H).
Could mean molecules of an element (H2),
which is hydrogen found in its natural state.
Could mean atoms of elements are present in
some form (sodium found in the human body).
Look at each particular case to determine its
proper use.
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Section 4.2
Symbols for the Elements
•
•
•
Each element has a unique one- or two-letter symbol.
First letter is always capitalized and the second is not.
The symbol usually consists of the first one or two
letters of the element’s name.

•
Examples:
Oxygen
Krypton
O
Kr
Sometimes the symbol is taken from the element’s
original Latin or Greek name.

Examples:
Gold Au
Lead Pb
aurum
plumbum
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Section 4.2
Symbols for the Elements
Names and Symbols of the Most Common Elements
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Section 4.3
Dalton’s Atomic Theory
1. Most natural materials are mixtures of pure
substances.
2. Pure substances are either elements or
combinations of elements called compounds.
3. A given compound always contains the same
proportions (by mass) of the elements.
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Section 4.3
Dalton’s Atomic Theory
Law of Constant Composition
•
A given compound always has the same
composition, regardless of where it comes
from.


Water always contains 8 g of oxygen for every 1 g of
hydrogen.
Carbon dioxide always contains 2.7 g of oxygen for
every 1 g of carbon.
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Section 4.3
Dalton’s Atomic Theory
Dalton’s Atomic Theory (1808)
1. Elements are made of tiny particles called
atoms.
2. All atoms of a given element are identical.
3. The atoms of a given element are different from
those of any other element.
4. Atoms of one element can combine with atoms
of other elements to form compounds. A given
compound always has the same relative
numbers and types of atoms.
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Section 4.3
Dalton’s Atomic Theory
Dalton’s Atomic Theory (continued)
5. Atoms are indivisible in chemical processes.
Atoms are not created or destroyed in
chemical reactions. A chemical reaction simply
changes the way the atoms are grouped
together.
ONLY NUCLEAR REACTIONS CAN
TRANSFORM ONE KIND OF ELEMENT TO
ANOTHER
4
2
2 He (
particle ) 
9
4B

12
6C

1
0n
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Section 4.3
Dalton’s Atomic Theory
Concept Check
Which of the following statements regarding
Dalton’s atomic theory are still believed to be
true?
I. Elements are made of tiny particles called atoms.
II. All atoms of a given element are identical.
III. A given compound always has the same relative
numbers and types of atoms.
IV. Atoms are indestructible.
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Section 4.4
Formulas of Compounds
Chemical Formulas Describe Compounds
•
Compound – distinct substance that is
composed of the atoms of two or more
elements and always contains exactly the
same relative masses of those elements.
•
Chemical Formulas – expresses the types of
atoms and the number of each type in each
unit (molecule) of a given compound.
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Section 4.4
Formulas of Compounds
Rules for Writing Formulas
1. Each atom present is represented by its element
symbol.
2. The number of each type of atom is indicated by a
subscript written to the right of the element symbol.
3. When only one atom of a given type is present, the
subscript 1 is not written.
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Section 4.4
Formulas of Compounds
Exercise
The pesticide known as DDT paralyzes insects by
binding to their nerve cells, leading to uncontrolled firing
of the nerves. Before most uses of DDT were banned in
the U.S., many insects had developed a resistance to it.
Write out the formula for DDT. It contains 14 carbon
atoms, 9 hydrogen atoms, and 5 atoms of chlorine.
C14H9Cl5
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Section 4.5
The Structure of the Atom
J. J. Thomson (1898—1903)
•
•
Postulated the existence of electrons using
cathode-ray tubes.
The atom must also contain positive particles
that balance exactly the negative charge
carried by particles that we now call electrons.
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Section 4.5
The Structure of the Atom
Cathode-Ray Tube
J.J. Thomson, measured mass/charge of eCopyright © Cengage Learning. All rights reserved
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Section 4.5
The Structure of the Atom
William Thomson (Plum Pudding Model)
•
Reasoned that the atom
might be thought of as a
uniform “pudding” of
positive charge with
enough negative
electrons scattered
within to counterbalance
that positive charge.
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Section 4.5
The Structure of the Atom
Ernest Rutherford (1911)
•
•
•
•
Explained the nuclear atom.
Atom has a dense center of positive charge
called the nucleus.
Electrons travel around the nucleus at a
relatively large distance.
A proton has the same magnitude of charge as
the electron, but its charge is positive.
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Section 4.5
The Structure of the Atom
Rutherford’s alpha particle scattering experiment.
5.5
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Section 4.5
The Structure of the Atom
Rutherford’s alpha particle scattering experiment.
Deflection and scattering of alpha particles by positive gold nuclei.
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Section 4.5
The Structure of the Atom
Rutherford and Chadwick (1932)
• Most nuclei also contain a neutral particle
called the neutron.
• A neutron is slightly more massive than a
proton but has no charge.
4
2

9
4B

12
6C

1
0n
α particle is a helium nucleus:
 Energy
4
2
He
2
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Section 4.5
The Structure of the Atom
• We know atoms are composed of
three main pieces - protons, neutrons
and electrons
• The nucleus contains protons and
neutrons
• The nucleus is only about 10-13 cm in
diameter
• The electrons move outside the
nucleus with an average distance of
about 10-8 cm
– therefore the radius of the atom is
about 100,000 times larger than the
radius of the nucleus
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Section 4.6
Introduction to the Modern Concept of Atomic Structure
The atom contains:
•
•
•
Electrons – found
outside the nucleus;
negatively charged
Protons – found in the
nucleus; positive charge
equal in magnitude to
the electron’s negative
charge
Neutrons – found in the
nucleus; no charge;
virtually same mass as a
proton
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Section 4.6
Introduction to the Modern Concept of Atomic Structure
•
The nucleus is:
 Small compared with the overall size of the
atom.
 Extremely dense; accounts for almost all of
the atom’s mass.
atomic radius ~ 100 pm = 1 x 10-10 m
nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m
“If the atom is the Houston Astrodome,
then the nucleus is a marble on the 50-yard
line.”
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Section 4.6
Introduction to the Modern Concept of Atomic Structure
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Section 4.6
Introduction to the Modern Concept of Atomic Structure
Why do different atoms have different chemical
properties?
•
•
•
The chemistry of an atom arises from its
electrons.
Electrons are the parts of atoms that
“intermingle” when atoms combine to form
molecules.
It is the number of electrons that really
determines chemical behavior.
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Section 4.7
Isotopes
Isotopes
•
•
•
Atoms with the same number of protons but
different numbers of neutrons.
Show almost identical chemical properties;
chemistry of atom is due to its electrons.
In nature most elements contain mixtures of
isotopes.
Mass Number
Atomic Number
1
1H
2
1H
(D)
3
1H
A
ZX
(T)
Element Symbol
235
92
U
238
92
U
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Section 4.7
Isotopes
Two Isotopes of Sodium
A – Z = n (number of neutrons)
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Section 4.7
Isotopes
Isotopes
A
Z
•
•
•
X
X = the symbol of the element
Z = the atomic number (# of protons)
A = the mass number (# of protons and
neutrons)
A – Z = n (number of neutrons)
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Section 4.7
Isotopes
Isotopes – An Example
14
6
•
•
•
C
C = the symbol for
carbon
6 = the atomic number
(6 protons)
14 = the mass number
(6 protons and 8
neutrons)
12
6
C
• C = the symbol for
carbon
• 6 = the atomic number
(6 protons)
• 12 = the mass number
(6 protons and 6
neutrons)
A – Z = n (number of neutrons)
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Section 4.7
Isotopes
Exercise
A certain isotope X contains 23 protons and 28
neutrons.
• What is the mass number of this isotope?
• Identify the element.
Mass Number = 51
Vanadium
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Section 4.8
Introduction to Periodic Table
The Periodic Table
•
The periodic table shows all of the known elements in
order of increasing atomic number.
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Section 4.8
Introduction to Periodic Table
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Section 4.8
Introduction to Periodic Table
• order elements by atomic mass
• saw a repeating pattern of properties
• Periodic Law – When the elements are arranged in
order of increasing relative mass, certain sets of
properties recur periodically
• used pattern to predict properties of undiscovered
elements
• where atomic mass order did not fit other properties,
he re-ordered by other properties
– Te & I
Mendeleev
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Section 4.8
Introduction to Periodic Table
Periodic Pattern
nm H2O
a/b
H
1
H2
m Li2O m/nm BeOnm B2O3 nm CO2 nm N2O5 nm
O2 nm OF2
Li b
Be a/b B a
C a N a
O
F
7 LiH 9 BeH2 11 ( BH3)n 12 CH4 14 NH3 16 H2O 19 HF
m Na2O m MgO m Al2O3 nm/m SiO2nm P4O10nm SO3 nm Cl2O7
Na b Mg b Al a/b Si a P a
S a Cl a
23 NaH24 MgH2 27 (AlH3) 28 SiH4 31 PH3 32 H2S 35.5 HCl
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Section 4.8
Introduction to Periodic Table
Mendeleev's Predictions for Ekasilicon (Germanium)
Property
Atomic
Mass
Color
Silicon’s
Props
28
Tin’s
Props
118
Grey
Grey
5.5
GreyWhite
5.4
Resists
Both
Resists
Both
Eks1O2
GeO2
Density
2.32
White
metal
7.28
Reaction
w/ Acid &
Base
Resists
Acid,
Reacts
Base
SiO2
Reacts
Acid,
Resists
Base
SnO2
Oxide
Predicted Measured
Value
Value
72
72.6
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Section 4.8
Introduction to Periodic Table
The Periodic Table
•
•
•
Metals vs. Nonmetals
Groups or Families – elements in the same
vertical columns; have similar chemical
properties
Periods – horizontal rows of elements
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Section 4.8
Introduction to Periodic Table
The Periodic Table
•
•
•
Most elements are metals and occur on the left side.
The nonmetals appear on the right side.
Metalloids are elements that have some metallic and
some nonmetallic properties.
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Section 4.8
Introduction to Periodic Table
= Alkali Metals
= Halogens
= Alkali Earth Metals
= Lanthanides
= Noble Gases
= Actinides
= Transition Metals
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Section 4.9
4.8
Natural
States
the Elements
Introduction
toof
Periodic
Table
Physical Properties of Metals
1. Efficient conduction of heat and electricity
2. Malleability (they can be hammered into thin
sheets)
3. Ductility (they can be pulled into wires)
4. A lustrous (shiny) appearance
5. High densities
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Section 4.9
4.8
Natural
StatestoofPeriodic
the Elements
Introduction
Table
•
•
Most elements are very reactive.
Elements are not generally found in
uncombined form.
 Exceptions are:
• Noble metals – gold, platinum and silver
• Noble gases – Group 8
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Section 4.9
4.8
Natural
StatestoofPeriodic
the Elements
Introduction
Table
Diatomic Molecules
•
Nitrogen gas contains N2
molecules.
• Oxygen gas contains O2
molecules.
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Section 4.9
4.8
Natural
StatestoofPeriodic
the Elements
Introduction
Table
Molecular Elements
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Section 4.9
4.8
Natural
Natural
States
States
oftoof
the
the
Elements
Elements
Introduction
Periodic
Table
Allotropes
• Different forms of a given element.
• Example:
– Solid carbon occurs in three forms.
• Diamond
• Graphite
• Buckminsterfullerene
Carbon Allotropes
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Section 4.10
4.8
Ions
Introduction
to Periodic Table
• Atoms can form ions by gaining or losing electrons.
– Metals tend to lose one or more electrons to form
positive ions called cations.
– Cations are generally named by using the name of
the parent atom.
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46
Section 4.10
4.8
Introduction to Periodic Table
Ions
•
Nonmetals tend to gain one or more electrons to form
negative ions called anions.
•
Anions are named by using the root of the atom name
followed by the suffix –ide.
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Section 4.10
4.8
Introduction to Periodic Table
Ions
Ion Charges and the Periodic Table
The ion that a particular atom will form can
be predicted from the periodic table.
Group or Family
Charge
Alkali Metals (1A)
1+
Alkaline Earth Metals (2A)
2+
Halogens (7A)
1–
Noble Gases (8A)
0
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Section 4.10
4.8
Introduction to Periodic Table
Ions
Ion Charges and the Periodic Table
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Section 4.10
4.8
Introduction to Periodic Table
Ions
Exercise
An ion with a 3+ charge contains 23 electrons.
Which ion is it?
–
–
–
–
a)
b)
c)
d)
Fe3+
V3+
Ca3+
Sc3+
+ve charge ≡ electrons are lost
-ve charge ≡ electrons are gained
# of e- = Z – positive charge
or
# of e- = Z + negative charge
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Section 4.10
4.8
Introduction to Periodic Table
Ions
Exercise
A – Z = n (number of neutrons)
A certain ion X1+ contains
54 electrons and 78
neutrons.
A 0
X
Z
Z = # of e- + positive charge
What is the mass number
or
of this ion?
Z = # of e- - negative charge
133
+ve charge ≡ electrons are lost
-ve charge ≡ electrons are gained
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Section 4.11
4.8
Introduction to
Compounds
That
Periodic
Contain
Table
Ions
•
•
Ions combine to form ionic compounds.
Properties of ionic compounds


High melting points
Conduct electricity
•
•
If melted
If dissolved in water
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Section 4.11
4.8
Introduction to
Compounds
That
Periodic
Contain
Table
Ions
•
•
Ionic compounds are electrically neutral.
The charges on the anions and cations in the
compound must sum to zero.
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Section 4.11
4.8
Introduction to
Compounds
That
Periodic
Contain
Table
Ions
Formulas for Ionic Compounds
•
•
Write the cation element symbol followed by the anion
element symbol.
The number of cations and anions must be correct for
their charges to sum to zero.
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Section 4.11
4.8
Introduction to
Compounds
That
Periodic
Contain
Table
Ions
Concept Check
A compound contains an unknown ion X and
has the formula XCl2. Ion X contains 20
electrons. What is the identity of X?
a)
b)
c)
d)
Ti2+
Sc+
Ca2+
Cr2+
Z = # of e- + positive charge
or
Z = # of e- - negative charge
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Section 4.11
4.8
Introduction to
Compounds
That
Periodic
Contain
Table
Ions
Concept Check
A member of the alkaline earth metal family
whose most stable ion contains 36 electrons
forms a compound with bromine. What is the
correct formula for this compound?
a)
b)
c)
d)
CaBr2
KrBr
RbBr
SrBr2
•
Ionic compounds are electrically
neutral.
•
The charges on the anions and
cations in the compound must sum
to zero.
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Section 4.8
Chapter
4 Homework
Introduction
to Periodic Table
Homework
• Reading assignment
– Pages 74 through 105
• Homework Problems: pages 107 - 111
– Questions and problems 3, 5, 9, 13, 19, 25, 27, 31,
33, 35, 37, 39, 42, 45, 47, 49, 51, 53, 57, 59, 61, 63,
67, 69, 71, 73, 75, 77, 81.
• Due on
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