Download Chapter 3

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Chapter 3
Atoms: The Building Blocks of Matter
This power point condenses the main ideas in Chapter 3 of your
textbook. Don’t forget that you can get a broader explanation of
these topics by reading the chapter!
Chapter 3 Atoms: the building blocks of matter
Bellwork:
1. 
Pick up 2 handouts, 1 piece of colored paper,
and 1 pair of scissors.
2. 
Cut out the title “The Evolution of the Atom”
and the 6 atom models. Examine the models
closely.
3. 
Lay the colored paper “landscape”. Place the
title at the top of the page. Then arrange the
models in the order in which you think they
were developed.
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Chapter 3 Atoms: the building blocks of matter
Evolution of the Atom
1. 
While you watch the video:
!  Rearrange your models, if necessary
!  Note the NAMES, DATES, and BIG IDEAS on your
notebook paper.
2. 
Glue the models to the colored paper in the correct
order. Write the info you collected under/next to each
model.
Chapter 3 Atoms: the building blocks of matter
Atoms
"  How did scientists recognize the existence of
something so small?
"  How small?
! 1 g of H gas contains 6.022 x 1023 atoms (six
hundred thousand billion-billion)
! This is the number of:
"  popcorn kernels needed to cover the U.S.
9 miles deep
"  cupfuls of water in Pacific Ocean
"  stacked soft drink cans that would cover the
Earth 200 miles deep
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Chapter 3 Atoms: the building blocks of matter
First ideas about matter date back to Greek
philosophers (not scientists)
" 
! 
Democritus (400 BC) developed an idea that matter
is made of indivisible particles he called atoms;
(atomos = uncuttable)
! 
Aristotle (350 BC) disagreed with Democritus; he
believed that matter was continuous and that all
matter was made of 4 elements (Earth, Fire, Water,
Air)
! 
Neither of them had experimental methods to
prove their ideas
! 
Aristotle’s ideas prevailed for the next 2000 years
Chapter 3 Atoms: the building blocks of matter
" 
By the late 1700’s, scientists had gathered evidence
favoring the idea that matter is made of atoms.
! 
Evidence:
law of conservation of mass – mass is neither
created nor destroyed during ordinary chemical
reactions or physical changes
" 
law of definite proportions – a chemical
compound always contains the same elements
in exactly the same proportion regardless of
how much of the compound you have or where
it came from
" 
law of multiple proportions – if different
compounds are made of the same 2 elements,
then the ratio of the masses of the second
element combined with a certain mass of the
first element is always a ratio of small whole
numbers
" 
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Chapter 3 Atoms: the building blocks of matter
Law of
Conservation of
Mass
Chapter 3 Atoms: the building blocks of matter
Law of Multiple Proportions
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Chapter 3 Atoms: the building blocks of matter
In 1808, John Dalton proposed an explanation
for the three laws in his Atomic Theory:
Dalton’s Atomic Theory
1. 
All matter is composed of extremely small particles called
atoms. Atoms can’t be subdivided, created, or destroyed.
2. 
Atoms of a given element are identical in size, mass, and other
properties; atoms of different elements differ in size, mass, and
other properties.
3. 
Atoms of different elements combine in simple whole-number
ratios to form chemical compounds.
4. 
In chemical reactions, atoms are combined, separated, or
rearranged.
Chapter 3 Atoms: the building blocks of matter
Modern Atomic Theory
Not all aspects of Dalton’s atomic theory have proven
to be correct. We now know that:
Atoms are divisible into even smaller particles.
A given element can have atoms with different
masses.
•  Some aspects of Dalton’s theory remain unchanged.
All matter is composed of atoms.
• 
Atoms of any one element differ in properties from
atoms of another element.
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Chapter 3 Atoms: the building blocks of matter
Modern Atomic Theory
" 
All atoms consist of two regions:
!  Nucleus – tiny, very dense, positively charged
region made up of protons (+) and neutrons (o)
!  Electron cloud – region occupied by extremely
tiny, negatively charged electrons
" 
But how did we discover this?????
Chapter 3 Atoms: the building blocks of matter
Discovery of the Electron
"  Cathode
Rays and Electrons
Experiments in the late 1800s showed that cathode
rays had mass and probably had a negative charge.
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Chapter 3 Atoms: the building blocks of matter
Discovery of the Electron
"  Charge
and Mass of the Electron
In 1897, JJ Thomson’s cathode-ray tube experiments
measured the charge-to-mass ratio of an electron. He
was able to conclude that all cathode rays are made of
identical negatively charged particles. These particles
were later named electrons.
Chapter 3 Atoms: the building blocks of matter
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Chapter 3 Atoms: the building blocks of matter
Discovery of the Electron, continued
"  Charge
and Mass of the Electron
Once the charge-to-mass ratio was known (Thomson),
scientists could measure either the charge or the mass
of one electron which would also yield the other.
In 1909, Robert A. Millikan’s oil drop experiment
measured the charge of one electron.
With this information, scientists were then able to
determine the mass of one electron.
Chapter 3 Atoms: the building blocks of matter
Discovery of the Atomic Nucleus
• 
More detail of the atom’s structure was provided in
1911 by Ernest Rutherford and his associates Hans
Geiger and Ernest Marsden.
• 
The results of their gold foil experiment led to the
following major conclusions:
•  The atom is mostly empty space.
•  Atoms contain a very dense, tiny, positively charged
bundle of matter at the center. Rutherford called
this positive bundle of matter the nucleus.
Later, in 1919, Rutherford discovered the proton.
• 
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Chapter 3 Atoms: the building blocks of matter
Gold Foil Experiment
Chapter 3 Atoms: the building blocks of matter
Gold Foil Experiment on the Atomic Level
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Chapter 3 Atoms: the building blocks of matter
Rutherford’s model of the atom
Chapter 3 Atoms: the building blocks of matter
In 1913, physicist Niels Bohr improved on Rutherford’s
model by proposing that electrons can circle the nucleus
only in allowed paths he called orbits. This model of the
atom was called the Bohr model.
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Chapter 3 Atoms: the building blocks of matter
In the 1920’s, Erwin Schrodinger further refined the
model of the atom. He proposed that electrons exist in
three-dimensional regions around the nucleus that
indicate the probable location of an electron. He called
these regions “orbitals”.
Chapter 3 Atoms: the building blocks of matter
In 1932, British physicist James Chadwick discovered the
neutron. The neutron is a neutral (no charge) particle
that is located in the nucleus of an atom.
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Chapter 3 Atoms: the building blocks of matter
Chapter 3 Atoms: the building blocks of matter
Modern Atomic Model:
the Quantum Mechanical Model
• 
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• 
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• 
• 
Except for the nucleus of the simplest type of hydrogen atom, all
atomic nuclei are made of protons and neutrons.
A proton has a positive charge equal in magnitude to the negative
charge of an electron.
Atoms are electrically neutral because they contain equal numbers
of protons and electrons.
A neutron is electrically neutral.
The nuclei of atoms of different elements differ in their number of
protons and therefore in the amount of positive charge they
possess.
Thus, the number of protons determines that atom’s identity.
Electrons exist in the electron cloud surrounding the nucleus.
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Chapter 3 Atoms: the building blocks of matter
Forces in the Nucleus
When two protons are extremely close to each other,
there is a strong attraction between them.
A similar attraction exists when neutrons are very close
to each other or when protons and neutrons are very
close together.
The short-range proton-neutron, proton-proton, and
neutron-neutron forces that hold the nuclear particles
together are referred to as nuclear forces.
Chapter 3 Atoms: the building blocks of matter
The Sizes of Atoms
• 
The radius of an atom is the distance from the center
of the nucleus to the outer portion of its electron cloud.
• 
Because atomic radii are so small, they are expressed
using a unit that is more convenient for the sizes of
atoms.
• 
This unit is the picometer, pm.
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Chapter 3 Atoms: the building blocks of matter
Properties of Subatomic Particles
Chapter 3 Atoms: the building blocks of matter
Atomic Number
• 
Atoms of different elements have different numbers of
protons.
• 
Atoms of the same element all have the same number
of protons.
• 
The atomic number (Z) of an element is the number
of protons of each atom of that element.
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Chapter 3 Atoms: the building blocks of matter
Atomic Number
Chapter 3 Atoms: the building blocks of matter
Isotopes
• 
Isotopes are atoms of the same element that have
different masses.
• 
The isotopes of a particular element all have the same
number of protons and electrons but different numbers of
neutrons.
• 
Most of the elements consist of mixtures of isotopes.
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Chapter 3 Atoms: the building blocks of matter
Mass Number
• 
The mass number is the total number of protons
and neutrons that make up the nucleus of an
isotope.
Chapter 3 Atoms: the building blocks of matter
Mass Number
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Chapter 3 Atoms: the building blocks of matter
Designating Isotopes
• 
Hyphen notation: The mass number is written with a
hyphen after the name (or symbol) of the element.
•  uranium-235
•  U-235
• 
Nuclear symbol: The superscript indicates the mass
number and the subscript indicates the atomic
number.
235
92
U
Chapter 3 Atoms: the building blocks of matter
Designating Isotopes
• 
The number of neutrons is found by subtracting the
atomic number from the mass number.
" 
" 
• 
mass number − atomic number = number of neutrons
235 (protons + neutrons) − 92 protons = 143 neutrons
Nuclide is a general term for a specific isotope of an
element.
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Chapter 3 Atoms: the building blocks of matter
Designating Isotopes
Sample Problem:
How many protons, electrons, and neutrons are there in an
atom of chlorine-37?
Solution:
atomic number = number of protons = number of electrons
mass number = number of neutrons + number of protons
An atom of chlorine-37 is made up of 17 protons, 17
electrons, and 20 neutrons.
Chapter 3 Atoms: the building blocks of matter
Atomic Mass
• 
• 
• 
• 
• 
• 
The mass of any atom comes from the protons and neutrons
in the nucleus (electrons have negligible mass).
The mass of one atom in grams is extremely small.
•  One atom of oxygen weighs 2.657 x 10-23 g
So scientists came up with a different unit for measuring the
mass of atoms.
One atomic mass unit, or 1 amu, is exactly 1/12 the mass
of a carbon-12 atom.
Since the mass of a carbon-12 atom comes from the 12
particles in the nucleus (protons + neutrons), 1 amu is
generally the mass of 1 proton or 1 neutron.
Therefore the atomic mass of any atom is its mass number
in amu’s.
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Chapter 3 Atoms: the building blocks of matter
Average Atomic Masses of Elements
Average atomic mass is the weighted average of the
atomic masses of the naturally occurring isotopes of an
element.
"  Calculating
• 
Average Atomic Mass
The average atomic mass of an element depends on
both the mass and the relative abundance of each of
the element’s isotopes.
Chapter 3 Atoms: the building blocks of matter
Average Atomic Masses of Elements
"  Calculating
Average Atomic Mass
Copper consists of:
•  69.15% copper-63, which has a mass of 63
amu
•  30.85% copper-65, which has a mass of 65
amu
The average atomic mass of copper can be calculated
by multiplying the mass of each isotope by its
relative abundance (expressed in decimal form) and
then adding the results.
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Chapter 3 Atoms: the building blocks of matter
Average Atomic Masses of Elements
"  Calculating
Average Atomic Mass,
(0.6915 × 63 amu) + (0.3085 × 65 amu) = 63.62 amu
The average atomic mass of copper is 63.62 amu.
Chapter 3 Atoms: the building blocks of matter
Relating Mass to Numbers of Atoms
"  The
• 
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Mole
The mole (mol) is the SI unit for amount of substance
Mole is a counting unit similar to a dozen
One mole of anything = 6.022 x 1023 of those things
(just like a dozen of anything = 12 of those things)
The number 6.022 x 1023 is called Avogadro’s number
Fun fact:
•  If every person living on Earth worked to count the atoms
in one mole of an element, and if each person counted
continuously at a rate of one atom per second, it would
take about 4 million years for all the atoms to be counted.
THAT’S A LOT OF ATOMS!!
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Chapter 3 Atoms: the building blocks of matter
Relating Mass to Numbers of Atoms
1 mole of
6.022 x 1023 atoms
atomic mass in
=
=
any element
of that element
grams
Examples:
1 mole of oxygen = 6.022 x 1023 atoms of oxygen = 16.00 g of O
1 mole of nitrogen = 6.022 x 1023 atoms of nitrogen = 14.00 g of N
1 mole of chlorine = 6.022 x 1023 atoms of chlorine = 35.45 g of Cl
Chapter 3 Atoms: the building blocks of matter
"  Molar
Mass
The atomic mass in grams of any element is called the
molar mass (mass of one mole).
Molar mass is written in units of g/mol.
Examples:
The molar mass of oxygen = 16.00 g/mol
The molar mass of nitrogen = 14.00 g/mol
The molar mass of chlorine = 35.45 g/mol
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Chapter 3 Atoms: the building blocks of matter
So what’s the
difference
between atomic
mass and molar
mass??
Chapter 3 Atoms: the building blocks of matter
Atomic Mass
Mass of one
atom
Molar Mass
Mass of one
MOLE of
atoms
Numerically
equivalent
Unit: amu
Unit: g/mol
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Chapter 3 Atoms: the building blocks of matter
Relating Mass to Numbers of Atoms
1 mole of
any element
23
= 6.022 x 10 atoms = molar mass
of that element
The relationship between moles, atoms, and molar mass
makes them useful as conversion factors:
Chapter 3 Atoms: the building blocks of matter
Solving Mole Problems
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Chapter 3 Atoms: the building blocks of matter
Relating Mass to Numbers of Atoms
" 
" 
Sample Problem
!  What is the mass in grams of 3.50 mol of the element copper, Cu?
Solution
!  Given: 3.50 mol Cu
!  Unknown:
mass of Cu (g)
!  Conversion factors to use:
Chapter 3 Atoms: the building blocks of matter
A chemical reaction produced 11.9 g
of Al. How many moles of Al
were produced?
11.9 g Al ×
1 mol Al
= 0.441 mol Al
26.98 g Al
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Chapter 3 Atoms: the building blocks of matter
How many moles of Ag are in
3.01 x 1023 atoms of Ag?
Chapter 3 Atoms: the building blocks of matter
What is the mass in grams of
1.20 x 1023 atoms of Cu?
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