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Chap 3: Atoms & the
Periodic Table
1
Pre-Question #1

What is an atom?


What particles make up an atom?


The basic unit of matter
Electrons, protons, and neutrons
What are three laws that support the
existence of atoms?
Law of definite proportions
 Law of conservation of mass
 Law of multiple proportions

2
Fold 2 pieces of paper as instructed
 Label the bottom

Law of definite proportions
 Law of conservation of mass
 Law of multiple proportion


On top, write 3 bullets points each of what
you learned from your reading
3
3-1. Foundations of Atomic Theory

The Laws of Definite Law of definite
proportion- in samples of any
chemical compound, the _____
massesof the
samples are always in the _____
same
______
proportions

ex: In water, there will always be 8 g O for 1
g of H.
16 g O = 8 g O
2gH
1gH
16 g
1g
1g
4
Chapter 3
Visual Concepts
Law of Definite Proportions
5
The Law of Conservation of Mass

The mass of the reactant in a reaction
equals the mass of the product
6
Chapter 3
Visual Concepts
Law of Conservation of Mass
7

Law of multiple proportion- whenever 2
elements form more than one compound,
the different
______ masses of one element that
same mass of the other
combine with the _____
element are in the ratio of small whole
numbers
 Ex:

compare water and peroxide.
Both molecules have the same number of H but
different number of O, so the ratio is 1:2.
water
peroxide
8
Chapter 3
Visual Concepts
Law of Multiple Proportions
9
 CO
 carbon
 CO2
monoxide
 carbon
dioxide
10
3-1. Development of Atomic Models
1.
2.
Greek model(300’s BC): Democritus
believed matter cannot be broken
atoms
forever_____
Dalton’s atomic theory (pg 78):
a.
b.
c.
d.
e.
Elements are composed of indivisible atoms
If same element, then same atoms
Cannot be subdivided, created, or destroyed
Can physically mix; can chemically combine
in whole # ratio
Chem. Rxn occur when atoms separate, join,
or rearrange
11
Chapter 1 Section Review

What is the atomic theory?


The theory that all matter is composed of
atoms
What is a compound?

A compound is a substance made from two or
more kinds of atoms
12

State the law of definite proportions,
conservation of mass and multiple
proportions

Law of definite proportions
 Each
sample of a given compound contains the
same elements in the same proportions by mass
regardless of the size or source of the sample

Law of conservation of mass
 Mass
is neither created nor destroyed during a
chemical reaction

Law of multiple proportions
 When
the same elements combine to form
different compounds, they do so in mass ratios that
can be expressed by small, whole numbers.
13

According to Dalton, what is the difference
between an element and a compound?
Element=composed of atoms, all have
identical properties
 Compound= two or more kinds of atoms, with
different properties, combined in a simple,
whole number ratio


Which of Dalton’s five principles still apply
to the structure of an atom?

Principles 3,4,5
 Principle
1= atoms can be divided into subatomic
particles
 Principle 2= isotopes exist with same atom,
different properties
14

What law is described by the fact that
carbon dioxide consists of 27.3% carbon
and 72.7% oxygen by mass?


Law of definite proportions
What law is described by the fact that the
ratio of the mass of oxygen in carbon
dioxide to the mass of oxygen in carbon
monoxide is 2:1?

Law of multiple proportions
15

Three compounds contain the element
sulfur and fluorine. How do the following
data support the law of multiple
proportions?
Compound A: 1.188g F for 1.000g S
Compound B: 2.375g F for 1.000g S
Compound C: 3.563g F for 1.000g S
 Three compounds have masses of F
combined with 1.000g of S in a ratio of small,
whole numbers. The ratio is 1.2.3
 Law of multiple proportions
16

Atoms and Periodic Table
17
3.
4.
5.
protons positive
Goldstein (1886): discovered______,
particles, observed canal rays traveling
opposite cathode rays
e- using a cathode-ray
Thomson: discovered __
tube(1897); its mass is about 1/2000 of a
hydrogen atom(1900) Fig 3-4, 3-5
Rutherford (1911): atom mostly empty space
with dense _______
nucleus
6.
Fig 3-6: gold foil experiment Gold Foil Experiment
one unit
Millikan(1916): e- carries ___
___ of negative
1/1840 of a
charge and has a mass of ______
7.
hydrogen atom
neutron no
Chadwick (1932): discovered _______,
charge, same mass as a proton
a.
18
Chapter 3
Visual Concepts
Comparing Models of Atoms
19
Chapter 3
Visual Concepts
Thompson’s Cathode Ray
Tube Experiment
20
Chapter 3
Visual Concepts
Rutherford’s Gold Foil
Experiment
21
3-2 Subatomic Particles
1.
Nucleus:
a.
b.
99.9% mass
protons
Isotope: same # of ______,
different # of
_______;
neutrons
- ex. 3 different isotopes of Ne: Ne-20, Ne-21, Ne-22
c.
d.
e.
2.
p+ = 1.673 x 10^-27 kg
Atomic mass = ______
_______
protons +neutrons
Atomic number = # of _______
protons
Electron:
a.
b.
Around the nucleus in a specific energy level
(Bohr)
9.109 x 10^-31 kg
22
Symbols
 Contain
the symbol of the element,
the mass number and the atomic
Mass
number.
number
Atomic
number
X
 We
can also put the mass number
after the name of the element for
different isotopes
 carbon-
12, carbon -14
Tr 12A Table 3 p. 83 Properties of Subatomic
Particles
Which is the smallest?
The Electron
Describe the information conveyed by each symbol.
The 1st symbol only shows the relative charge (use when that’s all
you need). The 2nd also shows the mass number.
SUBATOMIC PARTICLE
24
Subatomic Particles
ATOM
ATOM
NUCLEUS
NUCLEUS
PROTONS
PROTONS
POSITIVE
POSITIVE
CHARGE
ELECTRONS
ELECTRONS
NEUTRONS
NEUTRONS
NEGATIVE
CHARGE
NEGATIVE CHARGE
NEUTRAL
NEUTRAL
CHARGE
CHARGE
equal in a
Atomic
Most
ofNumber
the atom’s mass.
QUARKS
neutral atom
equals the # of...
25
B. Isotopes

Atoms of the same element with different
mass numbers.

Nuclear symbol:
Mass #
Atomic #

Hyphen notation: carbon-12
12
6
C
26
Example Problem
1. Give the Atomic number of the
element shown.
Ans. 9
2. Give the number of protons
and electrons for this
element.
Ans. 9 p+ and 9 e3. Give the mass number of the
Ans. 19
element shown.
4. Give the number of
neutrons for this element.Ans. 10
19
9
F
# of n0 = mass # - atomic #
# of n0 = 19 – 9 = 10 n0
Pre-Question #3

how many protons, neutrons and
electrons are in an atom of sodium with
atomic number of 11?
Atomic mass = 23 = # of protons + neutron
 Atomic number = 11 = # of protons and electrons
 Atomic mass – atomic number = # of neutron
 Therefore,

 11
proton, 11 electron
 12 neutron
28
29
B. Isotopes
30
© Addison-Wesley Publishing Company, Inc.
B. Isotopes

Chlorine-37

atomic #:
17

mass #:
37

# of protons:
17

# of electrons:
17

# of neutrons:
20
37
17
Cl
31

Isotope
32
Chapter 3.2 Section Review

Describe the difference between electrons,
protons and neutrons.

Electron
 the
mass is much smaller than proton and neutron.
 -1 charge
 Surrounds the nucleus

Proton and Neutron
 Make
up atomic nucleus
 +1 and no charge, respectively
33

How are isotopes of the same element
alike?


What subatomic particle was discovered
with the use of a cathode-ray tube?


All isotopes of an element have the same
number of protons and electrons
Electron
Write the symbol for element X, which has
22 electron
34

Determine the number of electrons, protons and
neutrons for each of the following

80-Br


106-Pd


46 e 46 p, 60 n
133-Cs


35 e, 35 p, 45 n
55 e, 55 p, 78 n
Calculate the atomic number and mass number
of an isotope that has 56 electrons and 82
neutrons


Atomic number = 56
Mass number 138
35

Why must there be an attractive force to
explain the existence of stable nuclei?


If the repulsive force between positively
charged protons were the only force, a
nucleus could not contain multiple protons.
Are hydrogen-3 and helium-3 isotopes of
the same element? Explain your answer

No, they are isotopes of different elements,
because they have different atomic numbers.
All isotopes of an element have the same
atomic number, not the same mass number.
36
3-4 Atomic Mass
Mass of atom at rest
 Refers to ONE atom
 The mass of an atom expressed in atomic
mass units
 amu = atomic mass unit

the ratio of the average mass per atom of the
element to 1/12 of the mass of 12C in its
nuclear and electronic ground state.
 Hydrogen = 1amu, 1/12 of C

37
Atomic Weight

the abundance-weighted average mass of
an element

Based on abundance of each element in nature.
Each isotope has its own atomic mass, thus we
determine the average from percent abundance.
Is not a whole number because it is an average.
are the decimal numbers on the periodic table.
Commonly reported in amu or grams/mol




Calculating Atomic Mass

Carbon has two stable isotopes
Carbon-12 has natural abundance of 98.89%
and 12.000 amu
Carbon-13 has natural abundance of 1.11% and
13.003 amu
Calculate the atomic mass
39
Carbon has two stable isotopes
Carbon-12 has natural abundance of 98.89% and 12.000 amu
Carbon-13 has natural abundance of 1.11% and 13.003 amu
Calculate the atomic mass
1.
2.
3.
Givens
Carbon-12 m=12.000 amu Abundance= 98.89%=0.9889
Carbon-13 m = 13.0003 amu Abundance = 1.11%=0.0111
Formula
atomic mass of carbon-avg
= (mass C-12 x nat.abund) + (mass C-13 x nat.abund.)
Plug in the #s
(12.000amu x 0.9889) + (13.003 amu x 0.0111)
= 12.011 amu
= 12.0 amu
40
Chemical Quantities?
 You
can measure mass, volume,or
you can count particles.
 measure mass in grams.
 measure volume in liters.
 We

count particles in MOLES.
Mole is abbreviated: mol
41
What is the Mole?
A counting number (like a dozen)
6.02 x 1023 is called Avogadro’s
number.
1 mol = 6.02  1023 items (
representative particles)
A
large amount!!!!
42

1 mole of hockey pucks would
equal the mass of the moon!

1 mole of basketballs would fill a
bag the size of the earth!

1 mole of pennies would cover the
Earth 1/4 mile deep!
43
Molar Conversion Examples
 How
many atoms are in 2.50
moles of C?
24
1.51

10
2.50 mol 6.02  1023 atoms
=atoms C
1 mol
44
Example
1. Calculate the # of atoms in 0.500 mol of Al.
1) Ans: 3.01 x 1023 Al atoms
0.500 mol Al x 6.02 x 1023 Al atoms
1 mol Al
2. Calculate the # of moles of Na if a sample of
Na contains 1.80 x 1024 Na atoms.
2) Ans:
2.99 mole Na
1.8 x 1024 Na atoms x
1 mol Na
6.02 x 1023 Na atoms
45
Molar Mass - Is the Mass (in Grams) of
One Mole of a Substance
(often called molecular weight)
Molar mass or MM
___ is the generic term for the
mass of one mole of any substance (in grams)

The same as:
1) gram molecular mass or gmm
___ (molecules)
2) gram formula mass or ___
gfm (ionic compounds)
3) gram atomic mass or gam
___ (elements)

46
Molar Mass of Elements = atomic mass
(simply look at the periodic table)

carbon
12.01 g/mol

aluminum
26.98 g/mol

zinc
65.39 g/mol
47
Mass to Mole Conversion
 How
many moles of carbon is 26
g of carbon? (find MM of C from
the periodic table)
26 g C 1 mol C
12.01 g C
= 2.2 mol C
48
Mass to Mole Conversion

How many moles is 5.69 g of Na?
 Na = 22.99 g/mol
5.69 g Na
1 mol Na
= 0.247 mol Na
22.99 g Na
49
Mole to Mass Conversion
How many grams are in 9.45 mol of
nitrogen atoms?
 N = 14.01 g/mol

9.45 mol N
14.01 g N
1 mol N
= 132.39 =132 g N
50
Molar Conversions
MASS
molar
mass
÷
X
NUMBER
MOLES
IN
GRAMS
6.02  1023
OF
X
÷
(g/mol)
(particles/mol)
PARTICLES
51
Test Prep:
How many moles of carbon-12 are
contained in exactly 6 grams of carbon12?
1.
2.
3.
4.
0.5mole
2.0moles
3.01 ×1023 moles
6.02 ×1023 moles
52
Test Prep
How many atoms are contained in 97.6 g of
platinum (Pt)?
1.
2.
3.
4.
5.16 × 1030
3.01 × 1023
1.20 × 1024
1.10 × 1028
53
What about compounds?
Mass in grams of 1 mole equal the
sum of the atomic masses
 What is the mass of one mole (molar
mass) of CH4?

1 C = 12.01 g/mol
4 H x 1.01 g/mol = 4.04g/mol
1 mole CH4 = 12.01g/mol + 4.04 g/mol
=16.05g/mol
54
Molar Mass Example Problem
Find the molar mass of sodium bicarbonate
NaHCO3
 22.99g/mol + 1.01g/mol + 12.01g/mol +
3(16.00 g/mol)
= 84.01 g/mol

55
Example Problem
Prozac, C17H18F3NO, is a widely used
antidepressant that inhibits the uptake of
serotonin by the brain. It has a molar
mass of
1) 40.0 g/mole
2) 262 g/mole
3) 309 g/mole
Solution: 17C (12.0)
18H (1.0)
3F (19.0)
1N (14.0)
+ 1 O (16.0)
309 g/mole
56
Mass to Mole Conversion

How many moles is 5.69 g of NaOH? (Find
MM of NaOH)
 Na = 22.99 g/mol
 O = 16.00 g/mol
 H = 1.01 g/ mol
40.00 g/mol
5.69 g NaOH
1 mol NaOH
= 0.142 mol NaOH
40.00 g NaOH
57
Mole to Mass Conversion
How many grams are in 9.45 mol of
dinitrogen trioxide?
 N2O3 = 2(14.01) + 3(16.00) = 76.02 g/mol

9.45 mol N2O3 76.02 g N2O3
= 718.2 =718 g N2O3
1 mol N2O3
58
Representative particles
 The
smallest pieces of a substance.
 molecular
compounds: molecule.
 ionic compounds: formula unit.
 elements: atom.
59
Questions

How many atoms in the following
cmpds?
CaCO3
5
Al2(SO4)3
17

How many oxygen atoms in the above
cmpds?
3
 12

60
A Moles of Particles
Contains 6.02 x 1023 particles
1 mole C
= 6.02 x 1023 C atoms
1 mole H2O
= 6.02 x 1023 H2O molecules
1 mole NaCl
= 6.02 x 1023 NaCl formula
units
61
Another Example
 How
many atoms of oxygen are
there in 1.23 moles of CO2 ?
23 molecules CO
6.02
x
10
1.23 mol CO2
2 2 atoms O
1 mol CO2
1 molecule CO2
= 1.48 x 1024 atoms O
62
More Molar Conversion
Examples
the mass of 2.1  1024
molecules of NaHCO3.
 Find
2.1  1024
molecules
1 mol
84.01 g
6.02  1023 1 mol
molecules
= 290 g NaHCO3
63
Practice Problems = .104 mol
1. How many moles is 4.56 g of CO2?
2. How many grams is 9.87 moles of
= 178 g
H2O?
3. How many molecules is 6.8 g of
23 molec
=
2.6
x
10
CH4?
4. How much would 3.45 x 1022 atoms
of U weigh?
= 13.6 g
64
Chapter 3
Standardized Test Preparation
Understanding Concepts
2. Which of these is always equal to the number of
protons in an atom?
F. the mass number
G. the number of isotopes
H. the number of neutrons
I. the number of electrons
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Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 3
Standardized Test Preparation
Understanding Concepts
2. Which of these is always equal to the number of
protons in an atom?
F. the mass number
G. the number of isotopes
H. the number of neutrons
I. the number of electrons
Chapter menu
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Chapter 3
Standardized Test Preparation
Understanding Concepts
3. Which of these events occurs when an electron in an
excited state returns to its ground state?
A. Light energy is emitted.
B. Energy is absorbed by the atom.
C. The atom undergoes spontaneous decay.
D. The electron configuration of the atom changes.
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Chapter 3
Standardized Test Preparation
Understanding Concepts
3. Which of these events occurs when an electron in an
excited state returns to its ground state?
A. Light energy is emitted.
B. Energy is absorbed by the atom.
C. The atom undergoes spontaneous decay.
D. The electron configuration of the atom changes.
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Chapter 3
Standardized Test Preparation
Reading Skills
7. The model of the atom has changed over time
because
F. earlier models were proven to be wrong.
G. electrons do not revolve around the nucleus.
H. as new properties of atoms were discovered,
models had to be revised to account for those
properties.
I. new particles were discovered, so the model had
to be changed to explain how they could exist.
Chapter menu
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Chapter 3
Standardized Test Preparation
Reading Skills
7. The model of the atom has changed over time
because
F. earlier models were proven to be wrong.
G. electrons do not revolve around the nucleus.
H. as new properties of atoms were discovered,
models had to be revised to account for those
properties.
I. new particles were discovered, so the model had
to be changed to explain how they could exist.
Chapter menu
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Chapter 3
Standardized Test Preparation
Reading Skills
8. Why do scientists need models as opposed to directly
observing electrons?
A. Models can be changed.
B. There is no technology that allows direct
observation of electrons.
C. The charges on the electrons and protons
interfere with direct observation of the atom.
D. Scientists cannot measure the speed of electrons
with sufficient accuracy to determine which model
is correct.
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Chapter 3
Standardized Test Preparation
Reading Skills
8. Why do scientists need models as opposed to directly
observing electrons?
A. Models can be changed.
B. There is no technology that allows direct
observation of electrons.
C. The charges on the electrons and protons
interfere with direct observation of the atom.
D. Scientists cannot measure the speed of electrons
with sufficient accuracy to determine which model
is correct.
Chapter menu
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Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 3
Standardized Test Preparation
Reading Skills
9. What would cause scientists to change the current
model of the atom?
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Chapter 3
Standardized Test Preparation
Reading Skills
9. What would cause scientists to change the current
model of the atom?
Answer: The current model of the atom would change if
new data were found about atoms that could not be
explained by the existing model. The new model would
explain both the new data and all earlier observations.
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Thomson’s Experiment
Voltage source
-
+
Vacuum tube
Metal Disks
Some History on The Discovery of the
Atom
Discovery of The Electron:
J.J. Thomson and the Cathode Ray Tube
(1897)
Calculated
e-/m
76
Thomson’s Experiment
Voltage source
 Passing
+
an electric current makes a
beam appear to move from the
negative to the positive end
Thomson’s Experiment
Voltage source
+
 By
adding an electric field
Thomson’s Experiment
Voltage source
+
 By
adding an electric field he found
that the moving pieces were negative
Rutherford’s experiment
Alpha particles - positively charged
particles- helium atoms minus electrons
 Shot them at gold foil which can be made
a few atoms thick.
 When an alpha particle hits a fluorescent
screen, it glows

Some History on The Discovery of the
Atom
Rutherford’s Gold Foil Experiment and
the Discovery of the Nucleus
Believed in Plum Pudding Model
Wanted to see How Large Atoms are
81
Lead
block
Uranium
Fluorescent
Screen
Gold Foil
He Expected
 The
alpha particles to pass through
without changing direction very much.
 Because…?
 …the positive charges were thought
to be spread out evenly. Alone they
were not enough to stop the alpha
particles.
What he expected
Because
He thought the mass was evenly
distributed in the atom
Since he thought the
mass was evenly
distributed in the atom
What he got
How he explained it
Atom is mostly empty.
 Small dense,
positive piece
at the center-the nucleus.
 Alpha particles
are deflected by
it, if they get close
enough.

+
Almost no deflection; few greatly deflected
+
History of Atom



Smallest possible
Democritus looked at
piece?
beach (400 B.C.)
Made of sand
Atomos - not to be cut
Cut sand - smaller sand