Topic
6
Table of Contents
Topic
6
Topic 6: Periodic Table
Basic Concepts
Additional Concepts
Periodic Table: Basic Concepts
Topic
6
The Search for a Periodic Table
• By 1860, scientists had already discovered 60
elements and determined their atomic masses.
• They noticed that some elements had similar
properties.
• They gave each group of similar elements a
name. Copper, silver, and gold were called
the coinage metals; lithium, sodium, and
potassium were known as the alkali metals;
chlorine, bromine, and iodine were called the
halogens.
Periodic Table: Basic Concepts
Topic
6
The Search for a Periodic Table
• Chemists also saw differences among the
groups of elements and between individual
elements.
• They wanted to organize the elements into a
system that would show similarities while
acknowledging differences.
• It was logical to use atomic mass as the basis
for these early attempts.
Periodic Table: Basic Concepts
Topic
6
Döbereiner’s Triads
• In 1829, the German chemist J.W. Döbereiner
classified some elements
into groups of three,
which he called triads.
• The elements in a triad had
similar chemical properties,
and their physical properties
varied in an orderly way
according to their atomic
masses.
Periodic Table: Basic Concepts
Topic
6
Döbereiner’s Triads
• Triads show a relationship among the densities
that is true for many triads. Density increases
with increasing atomic mass.
• Döbereiner’s triads were useful because they
grouped elements with similar properties and
revealed an orderly pattern in some of their
physical and chemical properties.
• The concept of triads suggested that the
properties of an element are related to its
atomic mass.
Periodic Table: Basic Concepts
Topic
6
Mendeleev’s Periodic Table
• The Russian chemist, Dmitri Mendeleev, was
a professor of chemistry at the University of
St. Petersburg when he developed a periodic
table of elements.
• Mendeleev was studying the properties of the
elements and realized that the chemical and
physical properties of the elements repeated in
an orderly way when he organized the
elements according to increasing atomic mass.
Periodic Table: Basic Concepts
Topic
6
•
•
•
•
Mendeleev’s Periodic Table
Mendeleev later developed an improved
version of his table with the elements
arranged in horizontal rows.
This arrangement was the forerunner of
today’s periodic table.
Patterns of changing properties repeated for
the elements across the horizontal rows.
Elements in vertical columns showed similar
properties.
Periodic Table: Basic Concepts
Topic
6
•
•
•
•
Mendeleev’s Periodic Table
Mendeleev’s insight was a significant
contribution to the development of chemistry.
He showed that the properties of the elements
repeat in an orderly way from row to row of
the table.
This repeated pattern is an example of
periodicity in the properties of elements.
Periodicity is the tendency to recur at regular
intervals.
Periodic Table: Basic Concepts
Topic
6
•
•
•
•
Mendeleev’s Periodic Table
One of the tests of a scientific theory is the
ability to use it to make successful predictions.
Mendeleev correctly predicted the properties
of several undiscovered elements.
In order to group elements with similar
properties in the same columns, Mendeleev
had to leave some blank spaces in his table.
He suggested that these spaces represented
undiscovered elements.
Periodic Table: Basic Concepts
Topic
6
Mendeleev’s Periodic Table
• Mendeleev was so confident of the periodicity
of the elements that he placed some elements
in groups with others of similar properties
even though arranging them strictly by atomic
mass would have resulted in a different
arrangement.
Periodic Table: Basic Concepts
Topic
6
Mendeleev’s Periodic Table
Periodic Table: Basic Concepts
Topic
6
Periodic Table of the Elements
Periodic Table: Basic Concepts
Topic
6
The Modern Periodic Table
• There are several places in the modern table
where an element of higher atomic mass
comes before one of lower atomic mass.
• This is because the basis for ordering the
elements in the table is the atomic number,
not atomic mass.
Periodic Table: Basic Concepts
Topic
6
The Modern Periodic Table
• The atomic number of an element is equal to
the number of protons in the nucleus.
• Atomic number
increases by one
as you move
from element to
element across a
row.
• Each row (except the first) begins with a
metal and ends with a noble gas.
Periodic Table: Basic Concepts
Topic
6
The Modern Periodic Table
• In between, the properties of the elements
change in an orderly progression from left
to right.
• The pattern in properties repeats after
column 18.
• This regular cycle illustrates periodicity in
the properties of the elements.
Periodic Table: Basic Concepts
Topic
6
The Modern Periodic Table
• The statement that the physical and chemical
properties of the elements repeat in a regular
pattern when they are arranged in order of
increasing atomic number is known as the
periodic law.
Periodic Table: Basic Concepts
Topic
6
Relationship of the Periodic
Table to Atomic Structure
• In the modern periodic table, elements are
arranged according to atomic number.
• The atomic number tells the number of
electrons it has.
Periodic Table: Basic Concepts
Topic
6
Relationship of the Periodic
Table to Atomic Structure
• If elements are ordered in the periodic table
by atomic number, then they are also
ordered according to the number of electrons
they have.
• The lineup starts with hydrogen, which has
one electron.
• Helium comes next in the first horizontal
row because helium has two electrons.
Lithium has three.
Periodic Table: Basic Concepts
Topic
6
Relationship of the Periodic
Table to Atomic Structure
• Notice on the periodic table that lithium
starts a new period, or horizontal row, in
the table.
• Why does this happen? Why does the first
period have only two elements?
• Only two electrons can occupy the first
energy level in an atom. The third electron
in lithium must be at a higher energy level.
Periodic Table: Basic Concepts
Topic
6
Relationship of the Periodic
Table to Atomic Structure
• Lithium starts a new period at the far left
in the table and becomes the first element
in a group.
• A group, sometimes also called a family,
consists of the elements in a vertical
column.
Periodic Table: Basic Concepts
Topic
6
Relationship of the Periodic
Table to Atomic Structure
• Groups are numbered from left to right.
• Lithium is the first element in Group 1 and
in Period 2. Check this location on the
periodic table.
Periodic Table: Basic Concepts
Topic
6
Relationship of the Periodic
Table to Atomic Structure
Periodic Table: Basic Concepts
Topic
6
Relationship of the Periodic
Table to Atomic Structure
• Elements with atomic numbers 4 through 10
follow lithium and fill the second period.
• Each has one more electron than the element
that preceded it.
• Neon, with atomic number 10, is at the end
of the period.
Periodic Table: Basic Concepts
Topic
6
Relationship of the Periodic
Table to Atomic Structure
• Eight electrons are added to Period 2 from
lithium to neon, so eight electrons must be
the number that can occupy the second
energy level.
Periodic Table: Basic Concepts
Topic
6
Relationship of the Periodic
Table to Atomic Structure
Periodic Table: Basic Concepts
Topic
6
Relationship of the Periodic
Table to Atomic Structure
• The next element, sodium, atomic number
11, begins Period 3.
• Sodium’s 11th electron is in the third
energy level.
• The third period repeats the pattern of the
second period. Each element has one more
electron than its neighbor to the left, and
those electrons are in the third energy level.
Periodic Table: Basic Concepts
Topic
6
Relationship of the Periodic
Table to Atomic Structure
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Period
• The first period is complete with two
elements, hydrogen and helium.
• Hydrogen has one electron in its outermost
energy level, so it has one valence electron.
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Period
• Every period after the first starts with a
Group 1 element.
• These elements have one electron at a
higher energy level than the noble gas of
the preceding period.
• Therefore, Group 1 elements have one
valence electron.
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Period
• As you move from one element to the next
across Periods 2 and 3, the number of
valence electrons increases by one.
• Group 18 elements have the maximum
number of eight valence electrons in their
outermost energy level.
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Period
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Period
• Group 18 elements are called noble gases.
• The noble gases, with a full complement of
valence electrons, are generally unreactive.
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Period
• The period number of an element is the same
as the number of its outermost energy level,
so the valence electrons of an element in the
second period, for example, are in the second
energy level.
• A Period 3 element such as aluminum has its
valence electrons in the third energy level.
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Period
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Group
• The number of valence electrons changes
from one to eight as you move from left to
right across a period; when you reach
Group 18, the pattern repeats.
• For the main group elements, the group
number is related to the number of
valence electrons.
• The main group elements are those in
Groups 1, 2, 13, 14, 15, 16, 17, and 18.
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Group
• For elements in Groups 1 and 2, the group
number equals the number of valence
electrons.
• For elements in Groups 13, 14, 15, 16, 17,
and 18, the second digit in the group number
is equal to the number of valence electrons.
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Period
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Group
• Because elements in the same group have the
same number of valence electrons, they have
similar properties.
• Sodium is in Group 1 because it has one
valence electron.
• Because other elements in Group 1 also
have one valence electron, they have similar
chemical properties.
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Group
• Chlorine is in Group 17 and has seven
valence electrons.
• All the other elements in Group 17 also have
seven valence electrons and, as a result, they
have similar chemical properties.
• Throughout the periodic table, elements in
the same group have similar chemical
properties because the have the same number
of valence electrons.
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Group
• Four groups have commonly used names:
the alkali metals in Group 1, the alkaline
earth metals in Group 2, the halogens in
Group 17, and the noble gases in Group 18.
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Group
• The word halogen is from the Greek words
for “salt former” so named because the
compounds that halogens form with metals
are saltlike.
• The elements in Group 18 are called noble
gases because they are much less reactive
than most of the other elements.
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Group
• Because the periodic table relates group and
period numbers to valence electrons, it’s
useful in predicting atomic structure and,
therefore, chemical properties.
Periodic Table: Basic Concepts
Topic
6
Atomic Structure of
Elements Within a Group
• For example, oxygen, in Group 16 and Period
2, has six valence electrons (the same as the
second digit in the group number), and these
electrons are in the second energy level
(because oxygen is in the second period).
• Oxygen has the same number of valence
electrons as all the other elements in Group 16
and, therefore, similar chemical properties.
Periodic Table: Basic Concepts
Topic
6
Electrons in Energy Levels—Group 16
Periodic Table: Basic Concepts
Topic
6
Physical States and
Classes of the Elements
• The color coding in the periodic table on
pages 92 and 93 identifies which elements
are metals (blue), nonmetals (yellow), and
metalloids (green).
Periodic Table: Basic Concepts
Topic
6
Physical States and
Classes of the Elements
• The majority of the elements are metals.
They occupy the entire left side and center
of the periodic table.
• Nonmetals occupy the upper-righthand corner.
• Metalloids are located along the
boundary between metals and nonmetals.
Periodic Table: Basic Concepts
Topic
6
Physical States and
Classes of the Elements
• Each of these classes has characteristic
chemical and physical properties, so by
knowing whether an element is a metal,
nonmetal, or metalloid, you can make
predictions about its behavior.
• Elements are classified as metals,
metalloids, or nonmetals on the basis of
their physical and chemical properties.
Periodic Table: Basic Concepts
Topic
6
Metals
• Metals are elements that have luster, conduct
heat and electricity, and usually bend without
breaking.
• With the exception of tin, lead, and bismuth,
metals have one, two, or three valence
electrons.
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movie clip.
Periodic Table: Basic Concepts
Topic
6
Metals
• All metals except mercury are solids at room
temperature; in fact, most have extremely high
melting points.
• The periodic table shows that most of the
metals (coded blue) are not main group
elements.
Periodic Table: Basic Concepts
Topic
6
Metals
• The elements in Groups 3 through 12 of the
periodic table are called the transition
elements.
• All transition elements are metals.
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movie clip.
Periodic Table: Basic Concepts
Topic
6
Metals
• Many are commonplace, including chromium
(Cr), iron (Fe), nickel (Ni), copper (Cu), zinc
(Zn), silver (Ag), and gold (Au).
• Some are less common but still important,
such as titanium (Ti), manganese (Mn), and
platinum (Pt).
• Some period 7 transition elements are
synthetic and radioactive.
Periodic Table: Basic Concepts
Topic
6
Metals
• In the periodic table, two series of elements,
atomic numbers 58-71 and 90-103, are placed
below the main body of the table.
• These elements are separated from the main
table because putting them in their proper
position would make the table very wide.
• The elements in these two series are known
as the inner transition elements.
Periodic Table: Basic Concepts
Topic
6
•
•
•
•
Metals
The first series of inner transition elements is
called the lanthanides because they follow
element number 57, lanthanum.
The lanthanides consist of the 14 elements
from number 58 (cerium, Ce) to number 71
(lutetium, Lu).
Because of their natural abundance on Earth
is less than 0.01 percent, the lanthanides are
sometimes called the rare earth elements.
All of the lanthanides have similar properties.
Periodic Table: Basic Concepts
Topic
6
Metals
• The second series of inner transition elements,
the actinides, have atomic numbers ranging
from 90 (thorium, Th) to 103 (lawrencium,
Lr).
• All of the actinides are radioactive, and none
beyond uranium (92) occur in nature.
• Like the transition elements, the chemistry of
the lanthanides and actinides is unpredictable
because of their complex atomic structures.
Periodic Table: Basic Concepts
Topic
6
Nonmetals
• Although the majority of the elements in the
periodic table are metals, many nonmetals
are abundant in nature
• The nonmetals
oxygen and
nitrogen make
up 99 percent of
Earth’s
atmosphere.
Periodic Table: Basic Concepts
Topic
6
Nonmetals
• Carbon, another nonmetal, is found in more
compounds than all the other elements
combined.
• The many
compounds of
carbon, nitrogen,
and oxygen are
important in a
wide variety of
applications.
Periodic Table: Basic Concepts
Topic
6
•
•
•
•
Nonmetals
Most nonmetals don’t conduct electricity, are
much poorer conductors of heat than metals,
and are brittle when solid.
Many are gases at room temperature; those
that are solids lack the luster of metals.
Their melting points tend to be lower than
those of metals.
With the exception of carbon, nonmetals have
five, six, seven, or eight valence electrons.
Periodic Table: Basic Concepts
Topic
6
Properties of Metals and Nonmetals
Periodic Table: Basic Concepts
Topic
6
Metalloids
• Metalloids have some chemical and physical
properties of metals and other properties of
nonmetals.
• In the periodic
table, the
metalloids lie
along the
border between
metals and
nonmetals.
Topic
6
Metalloids
• Silicon (Si) is probably the most well-known
metalloid.
• Some
metalloids such
as silicon,
germanium
(Ge), and
arsenic (As) are
semiconductors.
Periodic Table: Basic Concepts
Topic
6
Metalloids
• A semiconductor is an element that does
not conduct electricity as well as a metal,
but does conduct slightly better than a
nonmetal.
• The ability of a semiconductor to conduct an
electrical current can be increased by adding
a small amount of certain other elements.
• Silicon’s semiconducting properties made the
computer revolution possible.
Periodic Table: Basic Concepts
Topic
6
Semiconductors and Their Uses
• Your television, computer,
handheld electronic
games, and calculator are
electrical devices that
depend on silicon
semiconductors.
• All have miniature electrical circuits that use
silicon’s properties as a semiconductor.
Periodic Table: Basic Concepts
Topic
6
Semiconductors and Their Uses
• You learned that metals generally are good
conductors of electricity, nonmetals are poor
conductors, and semiconductors fall in
between the two extremes.
Basic Assessment Questions
Topic
6
Question 1
Match each element in Column A with the
best matching description in Column B.
Each Column A element may match more
than one description from Column B.
Basic Assessment Questions
Topic
6
Question 1
Column A
1. strontium
2. chromium
3. iodine
Column B
a. halogen
b. alkaline earth metal
c. representative element
d. transition element
Basic Assessment Questions
Topic
6
Answers
1. strontium
b, c
2. chromium
d
3. iodine
a, c
Basic Assessment Questions
Topic
6
Question 2
How many valence electrons are in an atom
of each of the following elements?
a. magnesium
b. selenium
c. tin
Basic Assessment Questions
Topic
6
Answers
a. magnesium
2
b. selenium
6
c. tin
4
Periodic Table: Additional Concepts
Topic
6
Additional Concepts
Periodic Table: Additional Concepts
Topic
6
Periodic Trends
• The electron structure of an atom determines
many of its chemical and physical properties.
• Because the periodic table reflects the
electron configurations of the elements, the
table also reveals trends in the elements’
chemical and physical properties.
Periodic Table: Additional Concepts
Topic
6
Atomic radius
• The atomic radius is a measure of the size of
an atom.
• The larger the radius, the larger is the atom.
Periodic Table: Additional Concepts
Topic
6
Atomic radius
• Research shows that atoms tend to decrease
in size across a period because the nuclei are
increasing in positive charge while electrons
are being added to sublevels that are very
close in energy.
• As a result, the increased nuclear charge pulls
the outermost electrons closer to the nucleus,
making the atom smaller.
Periodic Table: Additional Concepts
Topic
6
Atomic radius
• Moving down through a group, atomic radii
increase.
• Even though the positive charge of the
nucleus increases, each successive element
has electrons in the next higher energy level.
Periodic Table: Additional Concepts
Topic
6
Atomic radius
• Electrons in these higher energy levels are
located farther from the nucleus than those
in lower energy levels.
• The increased size of higher energy level
outweighs the increased nuclear charge.
• Therefore, the atoms increase in size.
Periodic Table: Additional Concepts
Topic
6
Ionic radius
• When an atom gains or loses one or more
electrons, it becomes an ion.
• Because an electron has a negative charge,
gaining electrons produces a negatively
charged ion, whereas losing electrons
produces a positively charged ion.
Periodic Table: Additional Concepts
Topic
6
Ionic radius
• As you might expect, the loss of electrons
produces a positive ion with a radius that is
smaller than that of the parent atom.
• Conversely, when an atom gains electrons,
the resulting negative ion is larger than the
parent atom.
Periodic Table: Additional Concepts
Topic
6
Ionic radius
• Practically all of the elements to the left of
group 4A of the periodic table commonly
form positive ions.
• As with neutral atoms, positive ions become
smaller moving across a period and become
larger moving down through a group.
Periodic Table: Additional Concepts
Topic
6
Ionic radius
• Most elements to the right of group 4A
(with the exception of the noble gases in
group 8A) form negative ions.
• These ions, although considerably larger
than the positive ions to the left, also
decrease in size moving across a period.
• Like the positive ions, the negative ions
increase in size moving down through
a group.
Additional Assessment Questions
Topic
6
Question 1
For each of the following pairs, predict
which atom is larger.
a. Mg, Sr
d. Ge, Br
b. Sr, Sn
c. Ge, Sn
e. Cr, W
Additional Assessment Questions
Topic
6
Answers
a. Mg, Sr
Sr
b. Sr, Sn
Sr
c. Ge, Sn
Sn
d. Ge, Br
Ge
e. Cr, W
W
Additional Assessment Questions
Topic
6
Question 2
For each of the following pairs, predict
which atom or ion is larger.
a. Mg, Mg2+
d. Cl–, I–
b. S, S2–
e. Na+, Al3+
c. Ca2+, Ba2+
Additional Assessment Questions
Topic
6
Answers
a. Mg, Mg2+
Mg
b. S, S2–
S2–
c. Ca2+, Ba2+
Ba2+
d. Cl–, I–
I–
e. Na+, Al3+
Na+
Additional Assessment Questions
Topic
6
Question 3
For each of the following pairs, predict which
atom has the higher first ionization energy.
a. Mg, Na
d. Cl, I
b. S, O
e. Na, Al
c. Ca, Ba
f. Se, Br
Additional Assessment Questions
Topic
6
Answers
a. Mg, Na
Mg
b. S, O
O
c. Ca, Ba
Ca
d. Cl, I
Cl
e. Na, Al
Al
f. Se, Br
Br
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