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Chapter 3
Atoms and Elements
3.1 Elements and Symbols
Elements are
• pure substances that cannot be separated into simpler
•
substances by ordinary laboratory processes.
the building blocks of matter.
gold
carbon
aluminum
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Sources of Some Element Names
Some elements are named for planets, mythological figures, minerals,
colors, scientists, and places.
A symbol
•represents the name of an element.
•consists of 1 or 2 letters.
•starts with a capital letter
•With few elements use their own special symbols
1-Letter Symbols
C
carbon
N
nitrogen
S
sulfur
2-Letter Symbols
Co
cobalt
Ca
calcium
Au
gold
Mg
magnesium
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Physical Properties of Elements
Some physical properties of
copper are:
Color
Luster
Melting point
Boiling point
Conduction
of electricity
Conduction
of heat
Red-orange
Very shiny
1083 °C
2567 °C
Excellent
Excellent
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Example
Select the correct symbol for each.
A. Phosphorous
1) K
2) P
3) Ph
Select the correct name for each symbol.
A. Ne
1) neon
2) nitrogen
3) nickel
B. K
1) potassium
3) phosphorus
2) phlogiston
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3.3The Periodic Table
Development of the Periodic Table
Mendeleev’s Periodic Table (1871)
Until the discovery of the proton, the elements were typically
organized by increasing atomic weight.
The modern organization is by increasing atomic number.
Groups and Periods
On the periodic table,
• elements are arranged according to similar properties.
• groups contain elements with similar properties in vertical
columns.
• periods are horizontal rows of elements.
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Names of Some Representative
Elements
Group Numbers
•use the letter A for the representative elements (1A to 8A)
•and the letter B for the transition elements.
•also use numbers 1-18 to the columns from left to right.
Elements and the Periodic Table
Examples
Identify the element described by the following:
A. Group 7A (17), Period 4
1) Br
2) Cl
3) Mn
B. Group 2A (2), Period 3
1) beryllium
2) boron
3) magnesium
C. Group 5A (15), Period 2
1) phosphorus
2) arsenic
3) nitrogen
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Metals, Nonmetals, and Metalloids
The heavy zigzag line separates metals and
nonmetals.
• Metals are located to the left.
• Nonmetals are located to the right.
• Metalloids are located along the heavy zigzag line
between the metals and nonmetals.
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Metals, Nonmetals, and Metalloids on the
Periodic Table
The heavy zigzag line separates metals and
nonmetals.
• Metals are located to the left.
• Nonmetals are located to the right.
• Metalloids are located along the heavy zigzag line between the metals and
nonmetals.
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Physical properties
Metals
• are shiny and ductile.
• are good conductors of heat and electricity.
Nonmetals
• are dull, brittle, and poor conductors.
• are good insulators.
Metalloids
• are better conductors than nonmetals, but not as good as metals.
• are used as semiconductors and insulators.
SUMMARY
 Periods: 7 horizontal rows.
 Groups: 18 vertical columns.
 International standard: 1-18
 US system: 1A-8A, 1B-8B
Examples
Identify each of the following elements as
1) metal, 2) nonmetal, or 3) metalloid.
A. sodium
B. iodine
C. Argon
D. iron
E. Silicon
____
____
____
____
____
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3.4 The Atom
The Law of Multiple Proportions and Dalton’s Atomic Theory
•
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.
•
The chemical combination of elements to make different
chemical compounds occurs when atoms join in small wholenumber ratios.
•
Chemical reactions only rearrange how atoms are combined in
chemical compounds; the atoms themselves don’t change.
Atomic Structure: 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.
Rutherford’s Gold Foil Experiment
In Rutherford’s gold foil experiment, positively
charged particles
•
were aimed at atoms of gold.
•
mostly went straight through the atoms.
•
were deflected only occasionally.
Conclusion:
There must be a small, dense, positively charged nucleus in the
atom that deflects positive particles that come close.
Subatomic Particles
Atoms contain subatomic particles.
•
•
•
•
Protons have a positive (+) charge.
Electrons have a negative (-) charge.
Neutrons are neutral.
Like charges repel and unlike charges
attract.
Structure of the Atom
An atom consists
• of a nucleus that
contains protons
and neutrons.
• of electrons in a
large, empty space
around the nucleus.
Atomic Mass Scale
On the atomic mass scale,
• 1 atomic mass unit (amu) has a mass equal to 1/12 of the mass of the
carbon-12 atom.
• a proton has a mass of about 1 (1.007) amu.
• a neutron has a mass of about 1 (1.008) amu.
• an electron has a very small mass, 0.000 549 amu.
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Examples
Identify each statement as describing a
1) proton, 2) neutron, or 3) electron.
A. found outside the nucleus
B. has a positive charge
C. is neutral
D. found in the nucleus
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Examples

Is each of the following statements true or false?
◦ Protons are heavier than electrons
◦ Protons are attracted to neutrons
◦ Electrons are small that they have no electrical charge
◦ The nucleus contains all the protons and neutrons of an
atom
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3.5 Atomic Number and Mass Number
The atomic number
• is specific for each element.
• is the same for all atoms of an element.
• is equal to the number of protons in an atom.
• appears above the symbol of an element.
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Atomic Number and Protons
What is the atomic number, number of proton and electrons in
•H atom:
•Na atom:
•Co atom:
•Se atom:
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Electrons in An Atom
An atom
• of an element is electrically neutral; the net charge of an atom is zero.
• has an equal number of protons and electrons.
number of protons = number of electrons
Aluminum has 13 protons and 13 electrons. The net
(overall) charge is zero.
13 protons + 13 electrons = 0
(+13)
+ (-13)
= 0 (neutral)
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Mass Number
The mass number
• represents the number of particles in the nucleus.
• is equal to the number of protons + the number of neutrons.
Element
Symbol
Atomic
number
Mass
number
p+
e-
n0
Carbon
C
6
12
6
6
0
Chlorine
Gold
37
79
2
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Examples
An atom of zinc has a mass number of 65.
A. How many protons are in this zinc atom?
1) 30
2) 35
3) 65
B. How many neutrons are in the zinc atom?
1) 30
2) 35
3) 65
C. What is the mass number of a zinc atom that has
37 neutrons?
1) 37
2) 65
3) 67
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3.6 Isotopes and Atomic Mass
Isotopes
• are atoms of the same element that have different mass numbers.
• have the same number of protons, but different numbers of neutrons.
• Isoptic symbol
gives the mass number in the upper left corner
and the atomic number in the lower left corner
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Information from Atomic Symbols
Examples of number of subatomic particles for atoms
Atomic symbol
16
8
O
8 p+
8n
8 e-
31
P
15
15 p+
16 n
15 e-
65
Zn
30
…. p+
……n
….. e-
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Examples
Naturally occurring carbon consists of three isotopes: 12C, 13C, and 14C.
State the number of protons, neutrons, and electrons in each of the
following:
12C
13C
14C
6
6
6
protons
______
neutrons ______
electrons
______
______
______
______
______
______
______
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Examples
Write the atomic symbols for atoms with the following
subatomic particles:
A. 8 p+, 8 n, 8 e-
___________
B. 17p+, 20n, 17e-
___________
C. 47p+, 60 n, 47 e-
___________
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Atomic Mass
The atomic mass of an element
• is listed below the symbol of each element on the periodic
table.
• gives the mass of an “average” atom of each element
compared to 12C.
Na
22.99
• is not the same as the mass number.
• has the smallest unit of amu
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Examples
Using the periodic table, specify the atomic mass of
each element.
A. calcium
__________
B. aluminum
__________
C.
lead
D. barium
E.
iron
__________
__________
__________
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Isotopes of Sulfur
A sample of naturally
occurring sulfur contains
several isotopes with the
following abundances
Isotope %
abundance
32S
95.02
33S
0.75
34S
4.21
36S
0.02
Average mass of S is 32.07 amu
32S, 33S, 34S, 36S
16
16
16
16
3
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Calculating Atomic Mass
The calculation for atomic mass requires the
• percent(%) abundance of each isotope.
• atomic mass of each isotope of that element.
• sum of the weighted averages.
Report your answer to two decimal places
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Atomic Masses
Why is the atomic mass of the element carbon 12.01 amu?
carbon-12:
98.89 % natural abundance
12.00 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
Atomic Mass for Cl
The atomic mass of chlorine is
• due to all the Cl isotopes.
• not a whole number.
• the average of two isotopes:
35Cl and 37Cl.
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7
Calculating Atomic Mass for Cl
35Cl
has atomic mass 34.97 amu (75.76%) and 37Cl has atomic mass
36.97 amu (24.24%).
• Use atomic mass and percent of each isotope to calculate the
contribution of each isotope to the weighted average.
Atomic mass 35Cl x % abundance =
Atomic mass 37Cl x % abundance =
• Sum is atomic mass of Cl is
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