Chapter Introduction
Lesson 1
Electrons and
Energy Levels
Lesson 2
Compounds,
Chemical
Formulas, and
Covalent Bonds
Lesson 3
Ionic and Metallic Bonds
Chapter Wrap-Up
How do elements
join together to form
chemical bonds?
What do you think?
Before you begin, decide if you agree or
disagree with each of these statements.
As you view this presentation, see if you
change your mind about any of the
statements.
Do you agree or disagree?
1. Elements rarely exist in pure form.
Instead, combinations of elements
make up most of the matter around
you.
2. Chemical bonds that form between
atoms involve electrons.
Do you agree or disagree?
3. The atoms in a water molecule are
more chemically stable than they would
be as individual atoms.
4. Many substances dissolve easily in
water because opposite ends of a
water molecule have opposite charges.
Do you agree or disagree?
5. Losing valence electrons can make
some atoms more chemically stable.
6. Metals are good electrical conductors
because they tend to hold onto their
valence electrons very tightly.
Electrons and Energy Levels
• How is an electron’s energy related to
its distance from the nucleus?
• Why do atoms gain, lose, or share
electrons?
Electrons and Energy Levels
• chemical bond
• valence electron
• electron dot diagram
The Periodic Table
• Elements on the periodic table are
organized in periods (rows) and groups
(columns).
• The periodic table lists elements in
order of atomic number, which
increases from left to right as you move
across a period.
The three main regions of elements on
the periodic table classify elements as
metals, nonmetals, or metalloids.
The Periodic Table (cont.)
• Except for hydrogen, elements on the
left side of the table are metals.
• Nonmetals are on the right side of the
table.
• Metalloids form the narrow stair-step
region between metals and nonmetals.
Atoms Bond
• A chemical bond is a force that holds
two or more atoms together in a
compound.
• Atoms contain protons, neutrons, and
electrons.
• Each proton has a positive charge; each
neutron has no charge; and each
electron has a negative charge.
Protons and
neutrons are in
an atom’s
nucleus.
Electrons move
around the
nucleus.
Atoms Bond (cont.)
• The atomic number of an element is the
number of protons in each atom of that
element.
• An electron moves around the nucleus at
a distance that corresponds to its
amount of energy.
Atoms Bond (cont.)
• Areas of space in which electrons move
around the nucleus are called energy
levels.
• Electrons closest to the nucleus have the
least amount of energy. Electrons
farthest from the nucleus have the
greatest amount of energy.
Electron Energy Levels
Atoms Bond (cont.)
How is an electron’s energy
related to its position in an atom?
Atoms Bond (cont.)
• The attraction between the positive
nucleus of one atom and the negative
electrons of another atom is what
creates a chemical bond.
• A valence electron is an outermost
electron of an atom that participates in
chemical bonding.
Atoms Bond (cont.)
valence
from Latin valentia, means
“strength, capacity”
The number of valence electrons in each
atom of an element can help determine the
type and number of bonds that an atom
can form.
The periodic table can tell you how many
valence electrons an atom has.
Atoms Bond (cont.)
In 1916 an American chemist named
Gilbert Lewis developed the electron dot
diagram, a model that represents valence
electrons in an atom as dots around the
element’s chemical symbol.
Atoms Bond (cont.)
• Atoms with eight valence electrons are
chemically stable and do not easily react
with other atoms.
• Atoms that have between one and seven
valence electrons are reactive or
chemically unstable and easily bond with
other atoms to form chemically stable
compounds.
Atoms Bond (cont.)
• The elements in group 18 are called
noble gases.
• With the exception of helium, noble
gases have eight valence electrons and
are chemically stable.
Atoms gain, lose, or share valence
electrons and become chemically stable.
Atoms Bond (cont.)
Why do atoms gain, lose, or
share electrons?
• Electrons are less
strongly attracted to
a nucleus the farther
they are from it,
similar to the way a
magnet attracts a
paper clip.
• Electrons in atoms
are in energy levels
around the nucleus.
Valence electrons
are involved in
chemical bonding.
• All noble gases,
except He, have
four pairs of dots in
their electron dot
diagrams. Noble
gases are
chemically stable.
Where on the periodic table are
nonmetals located?
A. the left side
B. the right side
C. the middle
D. all of the above
Which term refers to areas of
space in which electrons move
around the nucleus?
A. electron dot diagram
B. periodic table
C. neutron
D. energy levels
All of the elements in group 18
are called what?
A. metalloids
B. valence electrons
C. noble gases
D. metals
Do you agree or disagree?
1. Elements rarely exist in pure form.
Instead, combinations of elements
make up most of the matter around
you.
2. Chemical bonds that form between
atoms involve electrons.
Compounds, Chemical
Formulas, and Covalent Bonds
• How do elements differ from the
compounds they form?
• What are some common properties of
a covalent compound?
• Why is water a polar compound?
Compounds, Chemical
Formulas, and Covalent Bonds
• covalent bond
• molecule
• polar molecule
• chemical formula
From Elements to Compounds
• Compounds are chemical combinations
of different types of atoms.
• Chemical bonds join atoms together.
From Elements to Compounds (cont.)
bond
Science Use a force that holds
atoms together in a compound
Common Use a close personal
relationship between two people
From Elements to Compounds (cont.)
How is a compound different from
the elements that make it up?
Covalent Bonds—Electron Sharing
• A covalent bond is a chemical bond
formed when two atoms share one or
more pairs of valence electrons.
• A compound formed from many covalent
bonds is called a covalent compound.
Atoms with less than eight valence
electrons become chemically stable by
forming a chemical bond.
Covalent Bonds—Electron Sharing
(cont.)
• A single covalent bond exists
when two atoms share one pair of
valence electrons.
• A double covalent bond exists when
two atoms share two pairs of valence
electrons
• A triple covalent bond exists when two
atoms share three pairs of valence
electrons.
The more valence electrons that two atoms
share, the stronger the covalent bond is
between the atoms.
Covalent Compounds
• When two or more atoms share valence
electrons, they form a stable covalent
compound.
• Covalent compounds usually have low
melting points and low boiling points.
• They are usually gases or liquids at room
temperature, but they can also be solids.
• Covalent compounds are poor
conductors of thermal energy and
electricity.
Covalent Compounds (cont.)
What are some common properties
of covalent compounds?
Covalent Compounds (cont.)
• A molecule is a group of atoms held
together by covalent bonding that acts as
an independent unit.
• A molecule that has a partial positive end
and a partial negative end because of
unequal sharing of electrons is a polar
molecule.
Covalent Compounds (cont.)
polar
from Latin polus, means “pole”
Atoms of a polar molecule share their
valence electrons unequally.
Atoms of a nonpolar molecule share their
valence electrons equally.
Covalent Compounds (cont.)
Why is water a polar
compound?
Covalent Compounds (cont.)
• A chemical formula is a group of
chemical symbols and numbers that
represent the elements and the number
of atoms of each element that make up a
compound.
• A chemical formula describes the types
of atoms in a compound or a molecule,
but it does not explain the shape or
appearance of the molecule.
Chemical formulas and molecular models
provide information about molecules.
• A chemical formula is one way to
show the elements that make up a
compound.
• A covalent bond
forms when atoms
share valence
electrons. The
smallest particle
of a covalent
compound is a
molecule.
• Water is a polar
molecule
because the
oxygen and
hydrogen atoms
unequally share
electrons.
Which term refers to chemical
combinations of different types
of atoms?
A. covalent bond
B. chemical formula
C. compound
D. polar molecule
When two atoms share one pair
of valence electrons, which of the
following exists?
A. single covalent bond
B. double covalent bond
C. triple covalent bond
D. none of these
Which term refers to a molecule that
has a partial positive end and a
partial negative end because of
unequal sharing of electrons?
A. covalent bond
B. polar molecule
C. nonpolar molecule
D. covalent compound
Do you agree or disagree?
3. The atoms in a water molecule are
more chemically stable than they would
be as individual atoms.
4. Many substances dissolve easily in
water because opposite ends of a
water molecule have opposite charges.
Ionic and Metallic Bonds
• What is an ionic compound?
• How do metallic bonds differ from
covalent and ionic bonds?
Ionic and Metallic Bonds
• ion
• ionic bond
• metallic bond
Understanding Ions
An ion is an atom that is no longer
electrically neutral because it has lost or
gained valence electrons.
ion
from Greek ienai, means “to go”
Understanding Ions (cont.)
• Because electrons have a negative
charge, losing or gaining an electron
changes the overall charge of an atom.
• Atoms that lose valence electrons
become ions with a positive charge.
• Metal atoms, such as sodium, become
more stable when they lose valence
electrons and form a chemical bond with
a nonmetal.
Sodium atoms have a tendency to lose a
valence electron. Chlorine atoms have a
tendency to gain a valence electron.
Understanding Ions (cont.)
• Atoms are electrically neutral because
they have the same number of protons
and electrons.
• Once an atom gains or loses electrons,
it becomes a charged ion.
Ionic Bonds—Electron Transferring
• When forming a compound, the
nonmetal atoms gain the electrons lost
by the metal atoms.
• The attraction between positively and
negatively charged ions in an ionic
compound is an ionic bond.
An ionic bond forms between Na and Cl
when an Na atom transfers an electron to
a Cl atom.
Ionic Bonds—Electron Transferring
(cont.)
What holds ionic compounds
together?
Ionic Compounds
• Individual ions in an ionic compound are
strongly attracted to each other.
• Covalent compounds are made up of
many molecules.
• When nonmetal ions bond to metal ions
in an ionic compound there is a large
collection of oppositely charged ions and
no molecules.
Metallic Bonds—Electron Pooling
• A metallic bond is a bond formed when
many metal atoms share their pooled
valence electrons.
• Valence electrons in metals are not
bonded to one atom.
• Instead, a “sea of electrons” surrounds
the positive ions.
Valence electrons are free to move
among all the aluminum (Al) ions.
Metallic Bonds—Electron Pooling (cont.)
How do metal atoms bond with
one another?
Metallic Bonds—Electron Pooling (cont.)
• Metals are good conductors of thermal
energy and electricity.
• Metals are shiny because the valence
electrons at the surface of a metal
interact with light.
• Metal atoms lose
electrons and
nonmetal atoms
gain electrons and
form stable
compounds. An
atom that has
gained or lost an
electron is an ion.
• An ionic bond forms between positively
and negatively charged ions.
• A metallic bond
forms when
many metal
atoms share
their pooled
valence
electrons.
Which of these describes an atom
that is no longer electrically neutral
because it has lost or gained
valence electrons ?
A. covalent compound
B. proton
C. ion
D. molecule
What is a bond formed when
many metal atoms share their
pooled valence electrons?
A. ionic bond
B. metallic bond
C. covalent compound
D. ionic compound
An ionic bond is the attraction
between positively and negatively
charged ions in which of these?
A. valence electrons
B. covalent compound
C. ionic compound
D. none of these
Do you agree or disagree?
5. Losing valence electrons can make
some atoms more chemically stable.
6. Metals are good electrical conductors
because they tend to hold onto their
valence electrons very tightly.
Key Concept Summary
Interactive Concept Map
Chapter Review
Standardized Test Practice
Elements can join
together by sharing,
transferring, or pooling
electrons to make
chemical compounds.
Lesson 1: Electrons and Energy
Levels
• Electrons with more energy are farther from the
atom’s nucleus and are in a higher energy level.
• Atoms with fewer than
eight valence electrons
gain, lose, or share
valence electrons and
form stable compounds.
Atoms in stable
compounds have the
same electron arrangement as a noble gas.
Lesson 2: Compounds, Chemical
Formulas, and Covalent Bonds
• A compound and the elements it is
made from have different chemical
and physical properties.
• A covalent bond forms when two
nonmetal atoms share valence electrons.
Common properties of covalent compounds include
low melting points and low boiling points. They are
usually gas or liquid at room temperature and poor
conductors of electricity.
• Water is a polar compound because the oxygen
atom pulls more strongly on the shared valence
electrons than the hydrogen atoms do.
Lesson 3: Ionic and Metallic Bonds
• Ionic bonds form when valence electrons from a
metal atom transfers to a nonmetal atom.
• An ionic compound is held
together by ionic bonds, which
are attractions between positively
and negatively charged ions.
• A metallic bond forms when
valence electrons are pooled
among many metal atoms.
Which term refers to a force that
holds two or more atoms together
in a compound?
A. valence electron
B. positive charge
C. chemical bond
D. negative charge
Which of these is the outermost
electron of an atom that
participates in chemical bonding?
A. valence electron
B. nucleus
C. negative electrons
D. proton
Which of these is a group of atoms
held together by covalent bonding
that acts as an independent unit?
A. electron
B. proton
C. molecule
D. valence electrons
Which of these describes a
chemical bond formed when two
atoms share one or more pairs of
valence electrons?
A. polar molecule
B. covalent bond
C. chemical compound
D. none of these
A metallic bond is a bond formed
when many metal atoms share
what?
A. their pooled valence electrons
B. ions
C. charged ions
D. molecules
Which of these is a model that
represents valence electrons in
an atom as dots around the
element’s chemical symbol?
A. periodic table
B. energy level
C. atomic number
D. electron dot diagram
Which term describes atoms with
unpaired dots in their electron dot
diagrams?
A. reactive
B. chemically unstable
C. chemically stable
D. A and B
Which of these describes a group of
chemical symbols and numbers that
represent the elements and the
number of atoms of each element
that make up a compound?
A. chemical bond
B. chemical formula
C. covalent bond
D. molecule
Once an atom gains or loses
electrons, it becomes which of
these?
A. charged ion
B. covalent compound
C. molecule
D. proton
Which of these refers to the
attraction between positively and
negatively charged ions in an ionic
compound?
A. metallic bond
B. ionic bond
C. covalent compound
D. none of these