5.2 The Modern Periodic Table
The eight-note interval between any two notes on a keyboard
with the same name is an octave. The sounds of musical notes
that are separated by an octave are related, but they are not
identical. In a similar way, elements in the same column of the
modern periodic table are related but not identical.
5.2 The Modern Periodic Table
The Periodic Law
How is the modern periodic table organized?
5.2 The Modern Periodic Table
The Periodic Law
How is the modern periodic table organized?
In the modern periodic table, elements are
arranged by increasing atomic number
(number of protons).
5.2 The Modern Periodic Table
The Periodic Law
How is the modern periodic table organized?
In the modern periodic table, elements are
arranged by increasing atomic number
(number of protons).
Properties of elements repeat in a
predictable way when atomic numbers are
used to arrange elements into groups.
5.2 The Modern Periodic Table
The Periodic Law
The modern periodic table is based on atomic
number, or number of protons.
5.2 The Modern Periodic Table
The Periodic Law
Periods
Each row in the table of elements is a period.
• Hydrogen, the first element in Period 1, has one
electron in its first energy level.
• Lithium, the first element in Period 2, has one
electron in its second energy level.
• Sodium, the first element in Period 3, has one
electron in its third energy level.
• This pattern applies to all the elements in the
first column on the table.
5.2 The Modern Periodic Table
The Periodic Law
Groups
Each column in the periodic table is called a
group.
• The elements in a group have similar electron
configurations, so members of a group in the
periodic table have similar chemical properties.
• This pattern of repeating properties is the
periodic law.
5.2 The Modern Periodic Table
The Periodic Law
Periodic Table of the Elements
5.2 The Modern Periodic Table
Atomic Mass
What does the atomic mass of an element
depend on?
Atomic mass is a value that depends on the
distribution of an element’s isotopes in
nature and the masses of those isotopes.
5.2 The Modern Periodic Table
Atomic Mass
Atomic Mass Units
The mass of an atom in grams is extremely
small. In order to have a convenient way to
compare the masses of atoms, scientists
chose one isotope to serve as a standard.
• Scientists assigned 12 atomic mass units to the
carbon-12 atom, which has 6 protons and 6
neutrons.
• An atomic mass unit (amu) is defined as one
twelfth the mass of a carbon-12 atom.
5.2 The Modern Periodic Table
Atomic Mass
There are four pieces of information for each
element.
5.2 The Modern Periodic Table
Atomic Mass
There are four pieces of information for each
element.
Atomic number
5.2 The Modern Periodic Table
Atomic Mass
There are four pieces of information for each
element.
Atomic number
Element symbol
5.2 The Modern Periodic Table
Atomic Mass
There are four pieces of information for each
element.
Atomic number
Element symbol
Element name
5.2 The Modern Periodic Table
Atomic Mass
There are four pieces of information for each
element.
Atomic number
Element symbol
Element name
Atomic mass
5.2 The Modern Periodic Table
Atomic Mass
Isotopes of Chlorine
In nature, most elements exist as a mixture of
two or more isotopes. The element chlorine
has an atomic mass of 35.453 amu. Where
does the number 35.453 come from?
• There are two natural isotopes of chlorine,
chlorine-35 and chlorine-37.
• An atom of chlorine-35 has 17 protons and 18
neutrons.
• An atom of chlorine-37 has 17 protons and 20
neutrons.
5.2 The Modern Periodic Table
Atomic Mass
Weighted Averages
This table shows the atomic masses for the two
naturally occurring chlorine isotopes. The value of
the atomic mass for chlorine is a weighted average. If
you add the atomic masses of the isotopes and
divide by 2, you get 35.967, not 35.453.
5.2 The Modern Periodic Table
Classes of Elements
What categories are used to classify
elements on the periodic table?
5.2 The Modern Periodic Table
Classes of Elements
Elements are classified as metals,
nonmetals, and metalloids.
5.2 The Modern Periodic Table
Classes of Elements
The periodic table presents three different ways to
classify elements.
• State: solid—black symbol, liquid—purple symbol, or
gas—red symbol
• Occurrence in nature: elements that do not occur
naturally—white symbol.
• General properties: metal—blue background,
nonmetal—yellow background, or metalloid—green
background
5.2 The Modern Periodic Table
Classes of Elements
Metals
The majority of the elements on the periodic
table are classified as metals. Metals are
elements that are good conductors of electric
current and heat.
• Except for mercury, metals are solids at room
temperature.
• Most metals are malleable.
• Many metals are ductile; that is, they can be
drawn into thin wires.
5.2 The Modern Periodic Table
Classes of Elements
A When magnesium reacts with oxygen, a dull layer forms on its surface.
The layer can be removed to reveal magnesium’s shiny surface.
B Many telescope mirrors are coated with aluminum to produce a
surface that reflects light extremely well.
5.2 The Modern Periodic Table
Classes of Elements
The metals in groups 3 through 12 are called
transition metals. Transition metals are elements
that form a bridge between the elements on the left
and right sides of the table.
• Transition elements, such as copper and silver, were
among the first elements discovered.
• One property of many transition metals is their ability to
form compounds with distinctive colors.
5.2 The Modern Periodic Table
Classes of Elements
A compound of oxygen and the transition element
erbium is used to tint the pink glass lenses.
5.2 The Modern Periodic Table
Classes of Elements
Nonmetals
Nonmetals generally have properties
opposite to those of metals.
• Nonmetals are elements that are poor
conductors of heat and electric current.
• Nonmetals have low boiling points–many
nonmetals are gases at room temperature.
• Nonmetals that are solids at room temperature
tend to be brittle. If they are hit with a hammer,
they shatter or crumble.
5.2 The Modern Periodic Table
Classes of Elements
Fluorine is the most reactive nonmetal. The gases
in Group 18 are the least reactive elements in the
table. Some toothpastes use a compound of the
nonmetal fluorine and the metal sodium to help
prevent tooth decay.
5.2 The Modern Periodic Table
Classes of Elements
Metalloids
Metalloid elements are located on the periodic
table between metals and nonmetals.
• Metalloids are elements with properties that fall
between those of metals and nonmetals.
• For example, a metalloid’s ability to conduct
electric current varies with temperature. Silicon
(Si) and germanium (Ge) are good insulators at
low temperatures and good conductors at high
temperatures.
5.2 The Modern Periodic Table
Variations Across a Period
How do properties vary across a period in
the periodic table?
5.2 The Modern Periodic Table
Variations Across a Period
Across a period from left to right, the
elements become less metallic and more
nonmetallic in their properties.
5.2 The Modern Periodic Table
Variations Across a Period
From left to right across Period 3, there are three
metals (Na, Mg, and Al), one metalloid (Si), and four
nonmetals (P, S, Cl, and Ar).
5.2 The Modern Periodic Table
Variations Across a Period
• Sodium reacts violently with water.
• Magnesium will not react with water unless the
water is hot.
• Aluminum does not react with water, but it does
react with oxygen.
• Silicon is generally unreactive.
• Phosphorus and sulfur do not react with water,
but they do react with oxygen.
• Chlorine is highly reactive.
• Argon hardly reacts at all.
5.2 The Modern Periodic Table
Assessment Questions
1. What determines the atomic mass of an element?
a. the natural distribution of isotopes and the atomic
numbers of those isotopes
b. the natural distribution of isotopes and the masses of
those isotopes
c. the mass of the isotope of the element that has the most
neutrons
d. the average number of protons in the element’s nucleus
5.2 The Modern Periodic Table
Assessment Questions
1. What determines the atomic mass of an element?
a. the natural distribution of isotopes and the atomic
numbers of those isotopes
b. the natural distribution of isotopes and the masses of
those isotopes
c. the mass of the isotope of the element that has the most
neutrons
d. the average number of protons in the element’s nucleus
ANS: B
5.2 The Modern Periodic Table
Assessment Questions
2. Which of the following is not characteristic of
metals?
a.
b.
c.
d.
ductile
good electrical conductor
typically solid at room temperature
brittle
5.2 The Modern Periodic Table
Assessment Questions
2. Which of the following is not characteristic of
metals?
a.
b.
c.
d.
ductile
good electrical conductor
typically solid at room temperature
brittle
ANS:
D
5.2 The Modern Periodic Table
Assessment Questions
3. Within a period of the periodic table, how do the
properties of the elements vary?
a.
b.
c.
d.
Metallic characteristics increase from left to right.
Metallic characteristics decrease from left to right.
Reactivity increases from left to right.
Reactivity decreases from left to right.
5.2 The Modern Periodic Table
Assessment Questions
3. Within a period of the periodic table, how do the
properties of the elements vary?
a.
b.
c.
d.
Metallic characteristics increase from left to right.
Metallic characteristics decrease from left to right.
Reactivity increases from left to right.
Reactivity decreases from left to right.
ANS: B
5.2 The Modern Periodic Table
Assessment Questions
1. In the modern periodic table, elements are
arranged in order of increasing atomic mass.
True
False
5.2 The Modern Periodic Table
Assessment Questions
1. In the modern periodic table, elements are
arranged in order of increasing atomic mass.
True
False
ANS:
F, atomic number