Transcript Chapter 2

John E. McMurry • Robert C. Fay
C H E M I S T R Y
Fifth Edition
Chapter 2
Atoms, Molecules, and Ions
Lecture Notes
Alan D. Earhart
Southeast Community College • Lincoln, NE
Copyright © 2008 Pearson Prentice Hall, Inc.
Conservation of Mass and the
Law of Definite Proportions
Law of Conservation of Mass: Mass is neither
created nor destroyed in chemical reactions.
Aqueous solutions of mercury(II) nitrate and
potassium iodide will react to form a precipitate of
mercury(II) iodide and aqueous potassium iodide.
3.25 g + 3.32 g = 6.57 g
Hg(NO3)2(aq) + 2KI(aq)
HgI2(s) + 2KNO3(aq)
4.55 g + 2.02 g = 6.57 g
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Chapter 2/2
Conservation of Mass and the
Law of Definite Proportions
Law of Definite Proportions: Different samples of
a pure chemical substance always contain the
same proportion of elements by mass.
By mass, water is: 88.8 % oxygen
11.2 % hydrogen
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Chapter 2/3
Dalton’s Atomic Theory and the
Law of Multiple Proportions
•
Elements are made up of tiny particles called atoms.
•
Each element is characterized by the mass of its
atoms. Atoms of the same element have the same
mass, but atoms of different elements have different
masses.
•
Chemical combination of elements to make different
substances occurs when atoms join together in small
whole-number ratios.
•
Chemical reactions only rearrange the way that atoms
are combined; the atoms themselves don’t change.
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Chapter 2/4
Dalton’s Atomic Theory and the
Law of Multiple Proportions
Law of Multiple Proportions: Elements can combine
in different ways to form different substances, whose
mass ratios are small whole-number multiples of each
other.
nitric oxide:
nitrous oxide:
8 grams oxygen per 7 grams nitrogen
16 grams oxygen per 7 grams nitrogen
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Chapter 2/5
Dalton’s Atomic Theory and the
Law of Multiple Proportions
Law of Multiple Proportions: Elements can combine
in different ways to form different substances, whose
mass ratios are small whole-number multiples of each
other.
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Chapter 2/6
The Structure of Atoms:
Electrons
Cathode-Ray Tubes: J. J. Thomson (1856-1940)
proposed that cathode rays must consist of tiny
negatively charged particles. We now call them
electrons.
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Chapter 2/7
The Structure of Atoms:
Protons and Neutrons
Atomic Nucleus: Ernest Rutherford (1871-1937)
bombarded gold foil with alpha particles. Although
most of the alpha particles passed through the foil
undeflected, approximately 1 in every 20,000
particles were deflected. A fraction of those
particles were deflected back at an extreme angle.
Rutherford proposed that the atom must consist
mainly of empty space with the mass concentrated
in a tiny central core—the nucleus.
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Chapter 2/8
The Structure of Atoms:
Protons and Neutrons
The mass of the atom is
primarily in the nucleus
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Chapter 2/11
The Structure of Atoms:
Protons and Neutrons
The charge of the proton is
opposite in sign but equal
to that of the electron
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Chapter 2/12
Atomic Number
Atomic Number (Z): Number of protons in an
atom’s nucleus. Equivalent to the number of
electrons around the atom’s nucleus.
Mass Number (A): The sum of the number of
protons and the number of neutrons in an atom’s
nucleus.
Isotope: Atoms with identical atomic numbers but
different mass numbers.
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Chapter 2/13
Atomic Number
carbon-12
mass number
12
6
C
6 protons
6 electrons
6 neutrons
C
6 protons
6 electrons
8 neutrons
atomic number
carbon-14
mass number
14
6
atomic number
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Chapter 2/14
Atomic Mass
The mass of 1 atom of carbon-12 is defined to be 12 amu.
Atomic Mass: The weighted average of the isotopic
masses of the element’s naturally occurring isotopes.
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Chapter 2/15
Atomic Mass
Why is the atomic mass of the element carbon 12.01 amu?
carbon-12:
98.89 % natural abundance
12 amu
carbon-13:
1.11 % natural abundance
13.0034 amu
mass of carbon = (12 amu)(0.9889) + (13.0034 amu)(0.0111)
= 11.87 amu + 0.144 amu
= 12.01 amu
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Chapter 2/16
Compounds and Mixtures
Variable composition
Same composition
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Chapter 2/17
Compounds and Mixtures
Variable
properties
Similar
properties
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Chapter 2/18
Compounds and Mixtures
The same
number of
protons
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Cannot be
separated
physically
Chapter 2/19
Molecules, Ions, and Chemical
Bonds
Covalent Bond: Results when two atoms share
several (usually two) electrons. Typically a nonmetal
bonded to a nonmetal.
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Chapter 2/20
Molecules, Ions, and Chemical
Bonds
Ionic Bond: A transfer of one or more electrons from
one atom to another. An electrostatic attraction
between charged particles.Typically a metal bonded
to a nonmetal.
Ion: A charged particle.
Cation: A positively charged particle. Metals tend to
form cations.
Anion: A negatively charged particle. Nonmetals
tend to form anions.
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Chapter 2/21
Molecules, Ions, and Chemical
Bonds
In the formation of sodium chloride, one electron is
transferred from the sodium atom to the chlorine atom.
11 protons 17 protons
11 electrons 17 electrons
Na
+
Cl
Na1+
11 protons
10 electrons
+
Cl1-
17 protons
18 electrons
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Chapter 2/22
Molecules, Ions, and Chemical
Bonds
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Chapter 2/23
Acids and Bases
Acid: A substance that provides H1+ ions in water.
HCl, HNO3, H2SO4, H3PO4
Turns litmus red.
Base: A substance that provides OH1- ions in water.
NaOH, KOH, Ba(OH)2
Turns litmus blue.
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Chapter 2/24
Acids and Bases
H 2O
Hydrochloric acid:
H1+(aq) + Cl1-(aq)
HCl(g)
H 2O
Nitric acid:
H1+(aq) + NO31-(aq)
HNO3(l)
H 2O
Sulfuric acid:
H1+(aq) + HSO41-(aq)
H2SO4(l)
H 2O
HSO41-(aq)
H1+(aq) + SO42-(aq)
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Chapter 2/25
Acids and Bases
H 2O
Sodium hydroxide:
Na1+(aq) + OH1-(aq)
NaOH(s)
H 2O
Barium hydroxide:
Ba(OH)2(s)
Ba2+(aq) + 2OH1-(aq)
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Chapter 2/26
Naming Chemical Compounds
Cation Charges for Typical Main-Group Ions
1+
2+
3+
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Chapter 2/27
Naming Chemical Compounds
Anion Charges for Typical Main-Group Ions
3-
2- 1-
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Chapter 2/28
Naming Chemical Compounds
Some transition metals form more than one cation
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Chapter 2/29
Naming Chemical Compounds
Ionic Compound: A neutral compound in which the
total number of positive charges must equal the total
number of negative charges.
Binary Ionic Compounds
sodium chloride:
Na1+
Cl1-
NaCl
magnesium oxide:
Mg2+
O2-
MgO
aluminum sulfide:
Al3+
S2-
Al2S3
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Chapter 2/30
Naming Chemical Compounds
Stock System: Use Roman numerals in parentheses
to indicate the charge on metals that form more than
one kind of cation.
Binary Ionic Compounds
iron(III) oxide:
Fe3+
O2-
Fe2O3
tin(II) chloride:
Sn2+
Cl1-
SnCl2
lead(II) fluoride:
Pb2+
F1-
PbF2
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Chapter 2/31
Naming Chemical Compounds
Molecular Compound (Molecule): The unit of matter
that results when two or more atoms are joined by
covalent bonds.
Because nonmetals often combine
with one another in different
proportions to form different
compounds, numerical prefixes
are usually included in the names
of binary molecular compounds.
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Chapter 2/32
Naming Chemical Compounds
N2F4
The first element listed
is more cationlike and
takes the name of the
element.
The second element listed
is more anionlike and takes
the name of the element
with an “ide” modification
to the ending.
The prefix is added to the front of each to indicate
the number of each atom.
dinitrogen tetrafluoride
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Chapter 2/33
Naming Chemical Compounds
Binary Molecular Compounds
Whenever the prefix ends in “a” or “o” and the
element name begins with a vowel, drop the
“a” or “o” in the prefix.
N2O4
dinitrogen tetroxide
Whenever the prefix for the first element is
“mono,” drop it.
CO2
carbon dioxide
CO
carbon monoxide
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Chapter 2/34
Naming Chemical Compounds
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Chapter 2/35
Naming Chemical Compounds
Polyatomic Ionic Compounds
sodium hydroxide:
Na1+
OH1-
NaOH
magnesium carbonate:
Mg2+
CO32-
MgCO3
sodium carbonate:
Na1+
CO32-
Na2CO3
iron(II) hydroxide:
Fe2+
OH1-
Fe(OH)2
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Chapter 2/36
Naming Chemical Compounds
Binary Acids
HCl
hydrochloric acid
HBr
hydrobromic acid
HF
hydrofluoric acid
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Chapter 2/37
Naming Chemical Compounds
“ous”
“ic”
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“ite”
“ate”
Chapter 2/38