Chemistry

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Chemistry

• Chapter 3
• Atoms and Moles

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Chapter 3 Atoms and Moles

• Section 1 Substances are made of atoms

The atomic Theory
states that atoms are the building blocks of all
matter
What do you think an atom looks like?
Incorrect
More Accurate
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Chapter 3 Atoms and Moles

• Section 1 Substances are made of atoms

The Law of Definite Proportions
states that two samples of a given compound are
made of the same elements in exactly the same
proportions by mass regardless of the sizes or
sources of the samples.
Table salt (sodium chloride) is an example that
shows the law of definite proportions. Any
sample of table salt consists of two elements in
the following proportions by mass 60.66
chlorine and 39.34 sodium
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Chapter 3 Atoms and Moles

• Section 1 Substances are made of atoms

The Law of Conservation of Mass
states that the mass of the reactants in a
reaction equals the mass of the products
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Chapter 3 Atoms and Moles

• Section 1 Substances are made of atoms

The Law of Multiple Proportions
the law that states that when two elements
combine to form two or more compounds, the mass
of one element that combines with a given mass of
the other is in the ratio of small whole numbers
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Chapter 3 Atoms and Moles

• Section 1 Substances are made of atoms

Daltons Atomic Theory
According to Dalton, elements are composed of
only one kind of atom and compounds are made from
two or more kinds of atoms.
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Chapter 3 Atoms and Moles

• Section 1 Substances are made of atoms

Daltons atomic theory can be summarized by the
following statements
1. All matter is composed of extremely small
particles called atoms, which cannot be
subdivided, created, or destroyed.
2. Atoms of a given element are identical in
their physical and chemical properties.
3. Atoms of different elements differ in their
physical and chemical properties.
4. Atoms of different elements combine in simple,
whole-number ratios to form compounds.
5. In chemical reactions, atoms are combined,
separated, or rearranged but never created,
destroyed, or changed.
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Chapter 3 Atoms and Moles

• Section 1 Substances are made of atoms

Because some parts of Daltons theory have been
shown to be incorrect, his theory has been
modified and expanded as scientists learn more
about atoms.
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Chapter 3 Atoms and Moles

• For Homework
• 1. Do Concept Review
• Section 1 Substances are made of atoms
• 2. Read Chapter 3, Section 2 - Structure of Atoms

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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

Experiments by several scientists in the
mid-1800s led to the first change to Daltons
atomic theory.
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

The Discovery of Electrons by J.J. Thompson Mid
1800s
To study current, Thomson pumped most of the
air out of a glass tube. He then applied a
voltage to two metal plates, called electrodes,
which were placed at either end of the tube. One
electrode, called the anode, was attached to the
positive terminal of the voltage source, so it
had a positive charge. The other electrode,
called a cathode, had a negative charge because
it was attached to the negative terminal of the
voltage source. Thomson observed a glowing
beam that came out of the cathode and struck the
anode and the nearby glass walls of the tube. So,
he called these rays cathode rays. Thomson knew
the rays must have come from the atoms of the
cathode because most of the atoms in the air had
been pumped out of the tube. Thomson also
observed that when a small paddle wheel was
placed in the path of the rays, the wheel would
turn. This observation suggested that the cathode
rays consisted of tiny particles that were
hitting the paddles of the wheel.
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

Thomsons experiments showed that a cathode ray
consists of particles that have mass and a
negative charge.
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

Thomsons experiments showed that a cathode ray
consists of particles that have mass and a
negative charge. These particles are called
electrons
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

Thomson proposed that the electrons of an atom
were embedded in a Positively charged ball of
matter. His picture of an atom, which is shown in
was named the plum-pudding model
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

The Discovery of Nucleus by Ernest Rutherford 1909
Rutherfords team of researchers carried out
the experiment where a beam of small, positively
charged particles, called alpha particles, was
directed at a thin gold foil. The team measured
the angles at which the particles were deflected
from their former straight-line paths as
they came out of the foil. Rutherford found
that most of the alpha particles shot at the foil
passed straight through the foil. But a very
small number of particles were deflected, in some
cases backward. He went on to reason that only
a very concentrated positive charge in a tiny
space within the gold atom could possibly repel
the fast-moving, positively charged alpha
particles enough to reverse the alpha particles
direction of travel. Rutherford also
hypothesized that the mass of this
positive-charge containing region, called the
nucleus, must be larger than the mass of
the alpha particle.
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

This part of the model of the atom is still
considered true today. The nucleus is the dense,
central portion of the atom. The nucleus has all
of the positive charge, nearly all of the mass,
but only a very small fraction of The volume of
the atom.
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

By measuring the numbers of alpha particles that
were deflected and the angles of deflection,
scientists calculated the radius of the nucleus
to be less than 1/10,000 of the radius of the
whole atom.
If the nucleus of an atom were the size of a
marble, then the whole atom would be about the
size of a football stadium.
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

The positively charged particles that repelled
the alpha particles in the gold foil experiments
and that compose the nucleus of an atom
are called protons. The charge of a proton was
calculated to be exactly equal in magnitude but
opposite in sign to the charge of an electron.
Later experiments showed that the protons mass
is almost 2000 times the mass of an electron.
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

About 30 years after the discovery of the
electron, Irene Joliot-Curie Discovered that when
alpha particles hit a sample of beryllium, a beam
that could go through almost anything was
produced. The British scientist James Chadwick
found that this beam was not deflected by
electric or magnetic fields. He concluded that
the particles Carried no electric charge.
Further investigation showed that these
neutral particles, which were named neutrons are
part of all atomic nuclei
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

All atoms consist of protons and electrons.
Most atoms also have neutrons. Protons and
neutrons make up the small, dense nuclei of
atoms. The electrons occupy the space surrounding
the nucleus. For example, an oxygen atom has
protons and neutrons surrounded by electrons. But
that description fits all other atoms, such as
atoms of carbon, nitrogen, silver, and gold.
Elements differ from each other in the number of
protons their atoms contain.
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

Atomic Number and Mass Number
The number of protons that an atom has is known
as the atoms atomic number
The mass number is equal to the total number of
particles of the nucleus, that is protons plus
neutrons
Unlike the atomic number, which is the same for
all atoms of an element, mass number can vary
among atoms of a single element. In other words,
all atoms of an element have the same number of
protons, but they can have different numbers of
neutrons. These atoms of the same element are
called isotopes.
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

Calculating Proton, Electron and Neutron quantity
Proton Quantity is always equal to your atomic
number.
How many protons are in a silver atom?
47 protons
Which element has 25 protons in the nucleus?
Manganese
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

Calculating Proton, Electron and Neutron quantity
Neutron Quantity is always equal to your mass
atomic number
How many neutrons in an aluminum atom that has a
mass of 27amu?
14 neutrons
What is the mass of an atom of Iron that contains
30 neutrons?
56 amu
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

Calculating Proton, Electron and Neutron quantity
Electron Quantity using the following rules
For neutral atom
Electron quantity is equal to proton quantity
For positively charged atoms
Electron quantity is equal to proton quantity
minus the charge
For negatively charged atoms
Electron quantity is equal to proton quantity
plus the charge
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

Calculating Proton, Electron and Neutron quantity
How many electrons are in an oxygen atom with a
-2 charge?
10
How many electron in an atom of Potassium with a
1 charge?
18
What is the charge of a fluorine atom with 10
electrons?
Negative 1
What is the charge of a titanium atom with 22
electrons?
Neutral
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Chapter 3 Atoms and Moles

• Section 2 Structure of Atoms

1 amu
1
1-
0 amu
Neutral
1 amu
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How to display atoms with mass and charge
Mass number
Atomic Charge
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Na
10
Atomic Number
Carbon 14 or 14C or C-14 is a carbon atom
with a mass of 14amu
N-3 is a nitrogen atom with a charge of negative 3
30
25
7
55
25
-1
I
53
74
30
Zn
28
37
31
Neutral
Xe
131
54
38
50
38
2
76
Os
72
190
10
8
O
10
29
36
29
27
Rh
42
45
103
64
48
48
2
3
42
33
33
2
12
Mg
12
Ca
18
21
20
92
86
U
238
Fr
87
223
87
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All atoms of an element have the same atomic
number and the same number of protons. However,
atoms do not necessarily have the same number of
neutrons. Atoms of the same element that have
different numbers of neutrons are called isotopes
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How to calculate the average atomic mass on an
element.
Use the formula below
(mass
of atom1 x quantity1) (mass of atom2 x
quantity2) .. Average Atomic Mass

100
Average Atomic Mass (204 x 1.4) (206 x 24.1)
(207 x 22.1) (208 x 52.4)

100
Answer 207.2 amu
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Sample Questions
In a sample of the element potassium, each atom
has 1. 19 protons 2. 20 neutrons 3. 39 protons
and neutrons 4. 39 neutrons
In a sample of neutral copper, all atoms have
atomic numbers which are 1. the same and the
atoms have the same number of electrons 2. the
same, but the atoms have a different number of
electrons 3. different, but the atoms have the
same number of electrons 4. different and the
atoms have a different number of electrons
What is the mass number of an atom which contains
28 protons, 28 electrons and 34 neutrons? 1. 28
2. 56 3. 62 4. 90
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Sample Questions
Which of the following atoms has the greatest
nuclear charge? 1. Al 2. Ar 3. Si 4. Na
An atom of carbon-14 contains 1. 8 protons, 6
neutrons and 6 electrons 2. 6 protons, 6
neutrons and 8 electrons 3. 6 protons, 8
neutrons and 8 electrons 4. 6 protons, 8
neutrons and 6 electrons
Which particle contains the greatest number of
electrons? 1. Na 2. Na 3. F 4. F-
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Sample Questions
An electron has a charge of 1. -1 and the same
mass as a proton 2. 1 and the same mass as a
proton 3. -1 and a smaller mass than a proton
4. 1 and a smaller mass than a proton
What is the total number of electrons in a Cr3
ion? 1. 18 2. 21 3. 24 4. 27
A particle of matter contains six protons, seven
neutrons, and six electrons. This particle must
be a 1. neutral carbon atom 2. neutral nitrogen
atom 3. positively charged carbon ion 4.
positively charged nitrogen ion
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Sample Questions
If 75.0 of the isotopes of an element have a
mass of 35.0 amu and 25.0 of the isotopes have
a mass of 37.0 amu, what is the atomic mass of
the element? 1. 35.0 amu 2. 35.5 amu 3. 36.0
amu 4. 37.0 amu
Which symbol represents an isotope of carbon?
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Sample Questions
All isotopes of a given element must have the
same 1. atomic mass 2. atomic number 3. mass
number 4. number of neutrons
As the number of neutrons in the nucleus of a
given atom of an element increases, the atomic
number of that element 1. decreases 2. increases
3. remains the same
Which symbols represent atoms that are isotopes
of each other?
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Rutherfords Model Proposed Electron Orbits
The experiments of Rutherfords team led to the
replacement of the Plumpudding model of the atom
with a nuclear model of the atom. Rutherford
suggested that electrons, like planets orbiting
the sun, revolve around the nucleus in circular
or elliptical orbits.
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Bohrs Model Confines Electrons to Energy Levels
The Rutherford model of the atom, in turn, was
replaced only two years later by a model
developed by Niels Bohr, a Danish physicist. The
Bohr model describes electrons in terms of their
energy levels.
According to Bohrs model, electrons can be only
certain distances from the nucleus. Each distance
corresponds to a certain quantity of energy that
an electron can have.
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Electrons Act Like Both Particles and Waves
In 1924, Louis de Broglie pointed out that the
behavior of electrons according to Bohrs model
was similar to the behavior of waves.
The present-day model of the atom, which takes
into account both the particle and wave
properties of electrons. According to this model,
electrons are located in regions called Orbitals
around a nucleus that correspond to specific
energy levels. Orbitals are regions where
electrons are likely to be found. Orbitals are
sometimes called electron clouds because they do
not have sharp boundaries. When an orbital is
drawn, it shows where electrons are most likely
to be. Because electrons can be in other places,
the orbital has a fuzzy boundary like a cloud.
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Electron Configurations
The arrangement of electrons in an atom is
usually shown by writing an electron
configuration. Like all systems in nature,
electrons in atoms tend to assume arrangements
that have the lowest possible energies. An
electron configuration of an atom shows the
lowest-energy arrangement of the electrons for
the element.
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Principle Energy Levels (electron shells) Name
Max of e- 1 2 2 8 3 18 4 32 5 32 6 32 7
32
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Two types of electron configuration
Ground state When electrons are all found in
the lowest possible principle energy levels
(electron shell).
Excited state When one or more electrons have
jumped to a higher principle energy level
(electron shell).
Valence electrons The electrons found in the
outermost principle energy level (electron shell)
Octet Rule Atoms will gain or lose electrons to
try to have only 8 electrons in the last
principle energy level (electron shell). Very
small atoms only need 2 electrons to satisfy this
rule.
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Sample Questions
Which electron configuration is correct for a
sodium with a 1 charge? 1. 2-7 2. 2-8 3.
2-8-1 4. 2-8-2
How many electrons are in an Fe2 ion? 1. 24 2.
26 3. 28 4. 56
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Sample Questions
Which ion has the same electron configuration as
an H- ion? 1. Cl- 2. F- 3. K 4. Li
What is the total number of electrons in the
valence shell of an atom of aluminum in the
ground state? 1. 8 2. 13 3. 3 4. 10
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Sample Questions
Which element has an atom with the electron
configuration 2-8-8-2? 1. Mg 2. Ni 3. Ca 4.
Ge
Which set of symbols represents atoms with
valence electrons in the same electron shell? 1.
Ba, Br, Bi 2. Sr, Sn, I 3. O, S, Te 4. Mn,
Hg, Cu
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Sample Questions
Which symbol represents a particle that has the
same total number of electrons as S2-? 1. O2-
2. Si 3. Se2- 4. Ar
Which of these elements has an atom that
completes the octet rule? 1. Ne 2. Cl 3. Ca
4. Na
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Ions atoms that have lost or gained an electron
Cation an atom that has lost at least one
electron, thereby becoming positively charged.
Anion an atom that has gained at least one
electron, thereby becoming negatively charged.
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Sample Questions
What is the total number of valence electrons in
a fluorine atom in the ground state?  1. 5  2.
2  3. 7  4. 9
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
By 1900, scientists knew that light could be
thought of as moving waves that have given
frequencies, speeds, and wavelengths. In empty
space, light waves travel at 2.998 108 m/s. At
this speed, light waves take only 500 s to travel
the 150 million kilometers between the sun and
Earth. The wavelength is the distance between two
consecutive peaks or troughs of a wave. The
distance of a wavelength is usually measured
in meters. The wavelength of light can vary from
105 m to less than 10-13 m. This broad range of
wavelengths makes up the electromagnetic
spectrum. Our eyes are sensitive to only a small
portion of the electromagnetic spectrum. This
sensitivity ranges from 700 nm, which is about
the value of wavelengths of red light, to 400
nm, which is about the value of wavelengths of
violet light.
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Normally, if an electron is in a state of lowest
possible energy, it is in a ground state. If an
electron gains energy, it moves to an excited
state. An electron in an excited state will
release a specific quantity of energy as
it quickly falls back to its ground state. This
energy is emitted as certain wavelengths of
light, which give each element a unique
line-emission spectrum.
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
http//jersey.uoregon.edu/vlab/elements/Elements.h
tml
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Sample Questions
The diagram shows the characteristic spectral
line patterns of four elements. Also shown are
spectral lines produced by an unknown substance.
Which pair of elements is present in the unknown?
1. lithium and sodium 2. sodium and hydrogen
3. lithium and helium 4. helium and hydrogen
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Sample Questions
The characteristic bright-line spectrum of an
element is produced when its electrons 1. form
a covalent bond 2. form an ionic bond 3. move
to a higher energy state 4. return to a lower
energy state
When electrons in an atom in the excited state
fall to lower energy levels, energy is 1.
absorbed, only 2. released, only 3. neither
released nor absorbed 4. both released and
absorbed
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
What is the electron configuration of a sulfur
atom in the ground state? 1. 2-4 2. 2-6 3.
2-8-4 4. 2-8-6
Which electron transition represents a gain of
energy? 1. from 2nd to 3rd shell 2. from 2nd
to 1st shell 3. from 3rd to 2nd shell 4. from
3rd to 1st shell
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Chapter 3 Atoms and Moles
Section 3 Electron Configuration
Which is an electron configuration for an atom of
chlorine in the excited state? 1. 2-8-7 2.
2-8-8 3. 2-8-6-1 4. 2-8-7-1
Which electron configuration represents the
electrons of an atom in an excited state? 1.
2-4 2. 2-6 3. 2-7-2 4. 2-8-2
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Chapter 3 Atoms and Moles
Section 4 Counting Atoms
Obviously, atoms are so small that the gram is
not a very convenient unit for expressing their
masses. Even the picogram (10-12 g) is not very
useful. A special mass unit is used to express
this unit has two namesthe atomic mass unit
(amu) and the Dalton (Da). In this class, atomic
mass unit will be used.
Most samples of elements have great numbers of
atoms. To make working with these numbers easier,
chemists created a new unit called the
mole (mol). A is defined as the number of atoms
in exactly 12 grams of carbon-12.The mole is the
SI unit for the amount of a substance.
Chemists use the mole as a counting unit, just as
you use the dozen as a counting unit. Instead of
asking for 12 eggs, you ask for 1 dozen
eggs. Similarly, chemists refer to 1 mol of
carbon or 2 mol of iron.
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Chapter 3 Atoms and Moles
Section 4 Counting Atoms
To convert between moles and grams, chemists use
the molar mass of a substance. The gram molar
mass of an element is the mass in grams of one
mole of the element. Molar mass has the unit
grams per mol (g/mol). The mass in grams of 1 mol
of an element is numerically equal to the
elements atomic mass from the periodic table in
atomic mass units.
For example, the atomic mass of copper to two
decimal places is 63.55 amu. Therefore, the
molar mass of copper is 63.55 g/mol. Meaning that
63.55 grams of copper is equal to 1 mole of
copper.
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Chapter 3 Atoms and Moles
Section 4 Counting Atoms
Calculate the gram molar mass the following
substances.
H2O Bi(ClO3)3 N2O4 Ca(OH)2 Hg2S2O3 C6H12O6 CdO (NH
4)2Cr2O7
18 g/mol
459.5 g/mol
92.0 g/mol
74.1 g/mol
513.4 g/mol
180.0 g/mol
128.4 g/mol
252.0 g/mol
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Chapter 3 Atoms and Moles
Section 4 Counting Atoms
Converting between gram molar mass and moles.
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Chapter 3 Atoms and Moles
Section 4 Counting Atoms

• How many moles in 125.0 grams of PbI2?
• How many moles in 88.9 grams of Ne?
• How many moles in 500 grams of H2O?
• What is the mass of 5.6 moles of AgBr?
• What is the mass of 8.5 moles of MgO?
• What is the number of grams in 0.28 moles of K2O
• Calculate the mass of 0.058 moles of Hg2S

0.27 moles
4.4 moles
27.8 moles
1051.7 grams
342.6 grams
26.4 grams
25.1 grams
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Chapter 3 Atoms and Moles
Section 4 Counting Atoms
Scientists have also determined the number of
particles present in 1 mol of a substance,
called Avogadros number One mole of pure
substance contains 6.0221367 1023 particles.
Avogadros number may be used to count any kind
of particle, including atoms and molecules. For
calculations in this class ,Avogadros
number will be rounded to 6.022 1023 particles
per mole.
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Chapter 3 Atoms and Moles
Section 4 Counting Atoms
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Chapter 3 Atoms and Moles
Homework Pages 107-112 Due Thursday 1-12,
15-22, 24-36, 38, 42, 43, 45 Due Friday 46a-d,
48a-d, 53a-c, 54a-c, 55a-g, 56a-b, 57
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Chapter 3 Atoms and Moles
Chapter Review
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