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Atoms, Molecules, and Ions
Chapter 2
Chapter 2
1
The Atomic Theory of Matter
Dalton’s Theory of Matter:
1. Each element is composed of extremely small particles
call atoms.
2. All atoms of a given element are identical; atoms of
different elements are different.
3. Atoms of an element are not changed into different types
of atoms by a chemical reaction.
4. Compounds are formed when atoms of more than one
element combine.
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The Atomic Theory of Matter
Law of Constant Composition
In a given compound the relative numbers and kinds of
atoms are constant.
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The Atomic Theory of Matter
Law of Multiple Proportions
When two elements form different compounds, the
mass ratio of the elements in one compound is
related to the mass ratio in the other by a small
whole number.
Example:
Carbon Monoxide (CO)  12g C and 16g O
Carbon Dioxide (CO2)  12g C and 32g O
There is a 1:2 ratio of oxygen between the two
compounds.
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The Atomic Theory of Matter
Law of Conservation of Mass
The total mass of materials present after a chemical
reaction is the same as the total mass before the
reaction.
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The Discovery of Atomic Structure
Cathode Rays
• A cathode ray tube (CRT) is a hollow vessel with an
electrode at either end.
• The tube is evacuated and then partially filled with a
gas.
• A high voltage is applied across the electrodes and the
gas glows.
• Since glowing gas originates from the cathode, it is
referred to as a “Cathode Ray”.
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The Discovery of Atomic Structure
Cathode Ray
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The Discovery of Atomic Structure
Characteristics of Cathode Rays
• The rays are deflected by magnetic fields.
• Metal plates exposed to cathode rays acquire a
negative charge.
• The rays emitted are independent of the gas in the
cathode tube.
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The Discovery of Atomic Structure
Cathode Ray
Based on this information, it was determined that
cathode rays must be some fundamental particle.
Cathode rays are Electrons.
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The Discovery of Atomic Structure
Cathode Rays and Electrons
In 1897, Thomson determined the charge to mass ratio
of an electron to be 1.76  108 C/g.
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The Discovery of Atomic Structure
Cathode Rays and Electrons
• Millikan determined the charge on an electron to be
1.60 x 10-19 couloumbs.
• This was done with the oil drop experiment.
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The Discovery of Atomic Structure
Cathode Rays and Electrons
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The Modern View of Atomic Structure
3 Major Components of the Atom
• Proton
• Neutron
• Electron
positive (+) charge
no charge
negative (-) charge
1.0073 amu
1.0087 amu
0.000548 amu
The proton and neutron reside in the nucleus
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The Discovery of Atomic Structure
Radioactivity
Radioactivity - The spontaneous emission of radiation.
There are three types of radiation
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The Discovery of Atomic Structure
Radioactivity
1. Alpha particles (a)
a) Positive charge.
b) “Bare” helium atom.
c) Most massive, least penetrating radiation.
2. Beta particles (b)
a) Electron ejected from the nucleus.
b) Negative charge
3. Gamma Ray(g)
a) This is a ray, not a particle.
b) Most penetrating.
c) No charge
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The Discovery of Atomic Structure
The Nuclear Atom
Rutherford’s a-particle experiment:
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The Discovery of Atomic Structure
The Nuclear Atom
The a-particles were shot through a piece of gold foil.
• Most of the a-particles went straight through the foil
without deflection.
• A few of the particles were scattered.
• A very few of the particle were deflected back toward
the source.
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The Discovery of Atomic Structure
The Nuclear Atom
• Most of the volume of the atom must consist of a low
mass, diffuse negative charge (electron cloud).
• The center or nucleus of the atom must consist of a
dense positive charge.
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The Modern View of Atomic Structure
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The Discovery of Atomic Structure
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The Modern View of Atomic Structure
Isotopes, Atomic Numbers, and Mass Numbers
Atomic number (Z) = number of protons in the nucleus.
Mass number (A) = total number of protons and
neutrons in the nucleus.
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The Modern View of Atomic Structure
Isotopes, Atomic Numbers, and Mass Numbers
Atomic number (Z) = number of protons in the nucleus.
Mass number (A) = total number of protons and
neutrons in the nucleus.
A
Z
X
example :
12
6
C
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The Modern View of Atomic Structure
Isotopes, Atomic Numbers, and Mass Numbers
• In this series of elements, the mass number (A) varies but the
atomic number (Z) is constant.
• This means that we are looking at a series of isotopes.
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The Modern View of Atomic Structure
Isotopes, Atomic Numbers, and Mass Numbers
Isotope: Atom of an element with varying number of neutrons.
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The Periodic Table
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The Periodic Table
• Metals are located on the left hand side of the
periodic table (most of the elements are metals).
• Non-metals are located in the top right hand side of
the periodic table.
• Elements with properties similar to both metals and
non-metals are called metalloids and are located at
the interface between the metals and non-metals.
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The Periodic Table
• The elements in the periodic table are arranged in
such a way that substances that are chemically
similar are in a column.
• These columns are called groups.
• Columns are numbered from 1A to 8A or 1 to 18.
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The Periodic Table
Some of the groups in the periodic table are given
special names.
Group 1A: Alkali metals (Li….).
Group 2A: Alkaline earth metals (Be…).
Group 6A: Chalcogens (O…..).
Group 7A: Halogens (F….).
Group 8A: Noble gases (He…..).
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Molecules and Molecular Compounds
Molecular and Empirical Formulas
Molecule – an assembly of two or more atoms tightly
bound together.
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Molecules and Molecular Compounds
Molecular and Empirical Formulas
Molecular formula – A formula which gives the actual
number and type of atoms in a molecule.
Examples: H2O, CO2, CO, CH4, H2O2, O2, O3, and C2H4.
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Molecules and Molecular Compounds
Molecular and Empirical Formulas
Molecular formula – A formula which gives the actual
number and type of atoms in a molecule.
Empirical formula – A formula which gives the lowest
whole number ratio of atoms in a molecule.
Examples:
Substance
Benzene
Ethane
Water
Mol. formula
C 6 H6
C 2 H6
H2 O
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Empirical Formula
CH
CH3
H2 O
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Molecules and Molecular Compounds
Picturing Molecules
Structural Formula – A formula which shows how the
atoms of a molecule are joined.
• Structural formulas do not necessarily show the
three dimensional shape of the molecule.
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Molecules and Molecular Compounds
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Ions and Ionic Compounds
• If an electron is removed or added to a neutral atom
a charged particle or ion is formed.
• A positively charged ion is called a cation.
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Ions and Ionic Compounds
• If an electron is removed or added to a neutral atom
a charged particle or ion is formed.
• A positively charged ion is called a cation.
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Ions and Ionic Compounds
• If an electron is removed or added to a neutral atom
a charged particle or ion is formed.
• A positively charged ion is called a cation.
• A negatively charged ion is called an anion.
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Ions and Ionic Compounds
Predicting Ionic Charge
• Metals tend to form cations
• Non-metals tend to form anions.
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Ions and Ionic Compounds
Molecules can also gain or lose electrons and form
ions, They are called polyatomic ions.
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Ions and Ionic Compounds
Ion Name
Formula
Ion Name
Formula
Peroxide
O22-
Sulfate
SO42-
Triiodide
I3 -
Sulfite
SO32-
Ammonium
NH4+
Phosphate
PO43-
Nitrate
NO3-
Acetate
CH3CO2-
Nitrite
NO2-
Perchlorate
ClO4-
Hydroxide
OH-
Permanganate
MnO4-
Carbonate
CO32-
Dichromate
Cr2O72-
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Ions and Ionic Compounds
Ionic Compounds
Ionic Compound – A compound that contains positively
charged ions and negatively charged ions.
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Ions and Ionic Compounds
Ionic Compounds
Ionic Compound – A compound that contains positively
charged ions and negatively charged ions.
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Ions and Ionic Compounds
Predicting Formulas
Let’s consider a compound containing Mg and N.
• The common charge on Mg is +2 (or Mg2+).
• The common charge on N is –3 (or N3-).
• Since we want to make a neutral (uncharged)
compound, the total charges from the cations and
anions must cancel-out (or sum to zero).
• Therefore, Mg needs to lose 6 electrons (3  2+)
and N gain those 6 electrons (2  3-).
• The resulting formula is: Mg3N2.
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Naming Inorganic Compounds
Names and Formulas of Ionic Compounds
Naming of compounds (nomenclature) is divided into:
• organic compounds (those containing C)
• inorganic compounds (the rest of the periodic
table).
We will consider the naming rules of the Inorganic
compounds.
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Naming Ionic Compounds
1. Cations
a) Cations from metal atoms have the same name as
the metal.
b) If the cation can form more than one ion, the
positive charge is indicated by a roman numeral
in parenthesis.
c) Cations of non metals end in –ium.
P+3
phosphorium
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Naming Inorganic Compounds
Names and Formulas of Ionic Compounds
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Naming Inorganic Compounds
2. Anions
a) Monoatomic anions have names formed by
dropping the ending of the name of the element
and adding –ide.
b) Polyatomic anions containing oxygen have names
ending in –ate or –ite.
c) Anions derived by adding H+ to an oxyanion are
named by adding as a prefix the word hydrogen- or
dihydrogen-.
HSO4H2PO4-
Hydrogensulfate
Dihydrogenphsophate
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Naming Inorganic Compounds
3. Ionic Compounds
Name the compound by naming the cation
followed by the anion.
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Naming Inorganic Compounds
Names of Acids
1. Acids based on anions whose name end in –ide.
-ide becomes hydro- __________ -ic acid;
Cl-
Chloride
HCl
Hydrochloric Acid
F-
Fluoride
HF
Hydrofluoric Acid
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Naming Inorganic Compounds
Names of Acids
1. Acids based on anions whose name end in –ide.
-ide becomes hydro- __________ -ic acid;
2. Acids based on anions whose names end in
–ate or –ite.
-ate becomes -ic acid.
SO42- Sulfate
PO43- Phosphate
Sulfuric Acid
Phosphoric Acid
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Naming Inorganic Compounds
Names of Acids
1. Acids are based on anions whose name end in –ide.
-ide becomes hydro- __________ -ic acid;
2. Acids based on anions whose names end in
–ate or –ite.
-ate becomes -ic acid.
-ite becomes -ous acid.
SO32- Sulfite
PO33- Phosphite
Sulfurous Acid
Phosphorous Acid
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Naming Inorganic Compounds
Names and Formulas of Acids
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Naming Inorganic Compounds
Naming Binary Molecular Compounds
Binary molecular compounds have two elements.
1. The name of the left-most element is written first.
2. If the elements are in the same group the lower
element is written first.
3. The name of the second element ends in –ide.
4. Prefixes are used to indicate the number of atoms of
each element.
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Naming Inorganic Compounds
Naming Binary Molecular Compounds
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Naming Inorganic Compounds
Naming Binary Molecular Compounds
Binary molecular compounds have two elements.
1. The name of the left-most element is written first.
2. If the elements are in the same group the lower
element is written first.
3. The name of the second element ends in –ide.
4. Prefixes are used to indicate the number of atoms of
each element.
• Mono is never used in the first element.
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Naming Inorganic Compounds
Hydrobromic Acid
•
•
•
This is an acid based on a simple anion.
Hydrobromic Acid
The anion is Br-.
Since this is an acid, the cation is H+.
The formula is HBr.
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Naming Inorganic Compounds
Nitrous Acid
•
Since this acid ends in –ous Acid, this must be an
acid based on an oxide anion which end in -ite.
Nitrous Acid
Nitrite
•
The cation is H+.
•
The formula is: HNO2.
Chapter 2
NO2-
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Naming Inorganic Compounds
H2CO3
•
•
This is an acid formed from the carbonate anion.
Using the naming rules,
•
-ate is changed to –ic acid.
Carbonate  Carbonic Acid
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Naming Inorganic Compounds
N2O
•
•
•
•
This is a molecular compound.
The first element (N), just takes its name,
Nitrogen.
The second compound takes its name, ending in
-ide, Oxide.
Now we must consider how to show that there
are two nitrogen atoms, use di- as a prefix.
Dinitrogen Oxide
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Naming Inorganic Compounds
N2O5
•
•
•
•
•
This is a molecular compound.
The first element (N), just takes its name,
Nitrogen.
The second compound takes its name, ending in
-ide, Oxide.
Now we must consider how to show that there
are two nitrogen atoms, use di- as a prefix.
Finally, we must consider how to show that there
are five oxygen atoms, use penta- as a prefix.
Dinitrogen Pentoxide
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End of Chapter Problems
2.16, 2.18, 2.24, 2,30, 2.38,
2.42, 2.48, 2.54, 2.56
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