4.3 Elements, Isotopes, and Ions—
How Atoms Differ
Different Elements—
Different Numbers of Protons
• An element is a pure substance made from
atoms that all have the same number of
protons.
• Atoms of a particular element always have
the same number of protons.
4.3 Elements, Isotopes, and Ions—
How Atoms Differ
Different Elements—
Different Numbers of Protons
• The number of protons in an atom of an
element is the element’s atomic number.
• The periodic table shows elements that
increase in atomic number horizontally.
• Elements in the same column have similar
properties.
4.3 Elements, Isotopes, and Ions—
How Atoms Differ
Protons, Neutrons, and
Mass Number
• An atom’s mass number is the sum of the
number of protons and the number of
neutrons.
• To calculate the number of neutrons,
subtract the atomic number from the mass
number.
7.1 Organization of the Periodic Table
Periods
• A horizontal row of elements in the periodic
table is called a period.
• The atomic numbers increase by one from
left to right across a period.
7.1 Organization of the Periodic Table
Groups
• A vertical column of elements in the
periodic table is called a group.
• Groups are numbered 1–18 across the top
of the periodic table.
• Elements in the same group have similar
properties.
7.1 Organization of the Periodic Table
The Lanthanide and
Actinide Series
• The two rows of elements at the bottom of
the table are the Lanthanide Series and the
Actinide Series.
7.1 Organization of the Periodic Table
Metals
• Elements that are on the left side and in the
middle of the periodic table are metals.
7.1 Organization of the Periodic Table
Metals
• Metallic refers to the properties of
common metals.
• Luster, or shine, is one property of metals.
• Metals are also ductile and malleable.
• Conductivity is the ability of a material to
transfer electricity or thermal energy—
metals are good conductors.
7.1 Organization of the Periodic Table
Nonmetals
• Elements on the right side of the periodic
table are nonmetals.
7.1 Organization of the Periodic Table
Nonmetals
• Nonmetals exhibit properties that are the
opposite of metals.
• They are poor conductors of heat and
electricity, are brittle, and do not have luster.
• Nonmetals make up most of the matter in
the living world.
• The most reactive nonmetals are the
halogens in Group 17.
7.1 Organization of the Periodic Table
Semimetals
• A few elements are semimetals, or
metalloids.
7.1 Organization of the Periodic Table
Semimetals
• Semimetals have the properties of both
metals and nonmetals.
• Semimetals conduct electricity but not as
well as metals.
7.1 Organization of the Periodic Table
Noble Gases
• Group 18 elements are the noble gases.
• Noble gases are extremely stable by
themselves and occur in nature as single
atoms.