CHAPTER 6: CHEMICAL BONDS
STABLE ELECTRON CONFIGURATIONS
When is an atom unlikely to react?
When the highest occupied energy level of an atom
is filled with electrons, the atom is stable and not
likely to react.
STABLE ELECTRON CONFIGURATIONS
The chemical properties of an element depend on
the number of valence electrons.
An electron dot diagram is a model of an atom in
which each dot represents a valence electron. The
symbol in the center represents the nucleus and all
other electrons in the atom.
STABLE ELECTRON CONFIGURATIONS
STABLE ELECTRON CONFIGURATIONS
Noble gases are the most stable elements.
 The highest occupied energy level of a noble gas
atom is completely filled.
 The noble gases have stable electron
configurations with eight valence electrons (two
valence electrons in the case of helium)
 Elements tend to react to achieve electron
configurations similar to those of noble gases.
IONIC BONDS
What is one way in which elements can achieve
stable electron configurations?
Some elements achieve stable electron
configurations through the transfer of electrons
between atoms.
IONIC BONDS
Transfer of Electrons
 A sodium atom has one more electron than a
neon atom. Removing one electron would give
sodium a stable configuration.
IONIC BONDS
Transfer of Electrons
 A chlorine atom has one fewer electron than an
argon atom. Adding one electron would give
chlorine a stable configuration.
IONIC BONDS
When sodium reacts with chlorine, an electron is
transferred from each sodium atom to a chorine
atom. Each atom ends up with a more stable
electron arrangement than it had before the
transfer.
IONIC BONDS
Formation of Ions
When at atom gains or loses an electron, the
number of protons is no longer equal to the number
of electrons.
 The charge on the atom is not balanced, and the
atom is not neutral.
 An atom that has a net positive or negative
electric charge is called an ion.
 The charge on an ion is represented by a plus or
minus sign.
IONIC BONDS
A sodium ion has 11 protons and 10 electrons.
 The sodium ion has a charge of +1.
 The symbol for the ion is written Na+.
 An ion with a positive charge is a cation.
 A cation uses the element name, as in the sodium
ion.
IONIC BONDS
A chlorine ion has 17 protons and 18 electrons.
 This ion has a charge of -1.
 The symbol for the ion is written Cl-.
 An ion with a negative charge is called an anion.
 Anions like the Cl- ion are named by using the
beginning of the element name and the ending –
ide. The, Cl- is called a chloride ion.
IONIC BONDS
Formation of Ionic Bonds
A particle with a negative charge will attract a
particle with a positive charge.
 A chemical bond is the force that holds atoms
or ions together as a unit.
 An ionic bond is the force that holds cations and
anions together. An ionic bond forms when
electrons are transferred from one atom to
another.
IONIC BONDS
Ionization Energy
Cations form when electrons gain enough energy to
escape from atoms The energy allows electrons to
overcome the attraction of the protons in the
nucleus.
The amount of energy required to remove an
electron is called ionization energy. The lower
the ionization energy, the easier it is to remove an
electron from an atom.
IONIC BONDS
Ionization Energy
IONIC COMPOUNDS
How does the structure of an ionic compound affect
its properties?


Ionic compound particles are arranged in a
lattice structure called crystals.
The properties of an ionic compound can be
explained by the strong attractions among ions
within a crystal lattice.
IONIC COMPOUNDS
Compounds that contain ionic bonds are ionic
compounds, which can be represented by chemical
formulas.
 A chemical formula is a notation that shows
what elements a compound contains and the
ratio of the atoms or ions of those elements in the
compound.
 The chemical formula for sodium chloride, NaCl,
indicates one sodium ion for each chloride ion in
sodium chloride.
IONIC COMPOUNDS
What is the chemical formula for magnesium
chloride?
IONIC COMPOUNDS
What is the chemical formula for magnesium
chloride?
For each magnesium atom, you need two chlorine
atoms, one for each electron. The ratio is one
magnesium atom to two chlorine atoms, or MgCl2.
IONIC COMPOUNDS
Properties of Ionic Compounds
 Ionic compounds have high melting points

NaCl has a melting point of 801ºC
Solid ionic compounds are poor conductors of
electric current. When melted, they are good
conductors of electric current.
 Ionic compound crystals shatter when struck
with a hammer

ASSESSMENT QUESTIONS
1.
When is an atom stable?
a.
b.
c.
d.
When its electrons are evenly distributed through
its energy levels
When its lowest occupied energy level is filled with
electrons
When its highest unoccupied energy level is filled
with electrons
When its highest occupied energy level is filled with
electrons
Answer: D
ASSESSMENT QUESTIONS
2.
Which description applies to an element that
has two valence electrons.
a.
b.
c.
d.
Reactive metal
Nonreactive metal
Reactive nonmetal
Nonreactive nonmetal
Answer: A
ASSESSMENT QUESTIONS
3.
How do sodium and chlorine both achieve stable
electron configurations when they react?
a.
b.
c.
d.
An electron is transferred from the sodium atom to
the chlorine atom.
An electron is transferred from the chlorine atom to
the sodium atom.
Both atoms gain one electron.
Both atoms lose one electron.
Answer: A
ASSESSMENT QUESTIONS
4.
The ratio of aluminum ions to chloride ions in
aluminum chloride (AlCl3) is 3:1.
True
False
Answer: False, 1:3
COVALENT BONDS
How are atoms held together in covalent bonds?
A covalent bond is a chemical bond in which two
atoms share a pair of valence electrons.
The attractions between the shared electrons and
the protons in each nucleus hold that atoms
together in a covalent bond.
COVALENT BONDS
A hydrogen atom has one electron. If it had two
electrons it would have the same electron
configuration as a helium atom.
Two hydrogen atoms can achieve a stable electron
configuration by sharing their electrons and
forming a covalent bond.
When two atoms share one pair of electrons, the
bond is called a single bond.
COVALENT BONDS
There are several ways to show a covalent bond.
 In the electron dot model, the bond is shown by a
pair of dots in the space between the symbols.

In the structural formula, the pair of dots is
replaced by a line.
COVALENT BONDS
Molecules of Elements
Two hydrogen atoms bonded together form a unit
called a molecule.
A molecule is a neutral group of atoms that are
joined together by one or more covalent bonds.
COVALENT BONDS
The hydrogen molecule is neutral because it
contains two protons (one from each atom) and two
electrons (one from each atom).
A chemical formula can be used to describe the
molecules of an element as well as a compound.
The element hydrogen has the chemical formula
H2.
COVALENT BONDS
Many nonmetal elements exist
as diatomic molecules.
Diatomic means “two atoms.”
There are seven elements that
are diatomic.
In addition to the elements
shown on the right, oxygen (O2)
and hydrogen (H2) are the
other diatomic elements.
COVALENT BONDS
Multiple Covalent Bonds
When two atoms two pairs of electrons, the bond
is called a double bond.
When two atoms share three pairs of electrons,
the bond is called a triple bond.
In a nitrogen molecule, N2, the two nitrogen atoms
are connected by a triple bond.
In an oxygen molecule, O2, the two oxygen atoms
are connected by a double bond.
UNEQUAL SHARING OF ELECTRONS
What happens when atoms don’t share electrons
equally?
When two atoms form a covalent bond, sometimes
one of the atoms has a greater attraction for
electrons than the other. If this is the case, the
bond is a polar covalent bond, which means the
electrons are shared unequally.
UNEQUAL SHARING OF ELECTRONS
The atom with the greater attraction for electrons
has a partial negative charge and the other atom
has a partial positive charge.
Except for noble gases, elements on the right of the
periodic table tend to have a greater attraction for
electrons than element on the left.
Element at the top of a group tend to have a
greater attraction for electrons than elements at
the bottom of a group.
UNEQUAL SHARING OF ELECTRONS
Polar Covalent Bonds
In a molecule of an element, the atoms that form
covalent bonds are from the same element, so they
have the same ability to attract an electron. The
electrons are shared equally.
In a molecule of a compound, electrons may not be
shared equally.
UNEQUAL SHARING OF ELECTRONS
A covalent compound forms when hydrogen reacts
with chlorine.
 A chlorine atom has a greater attraction for
electrons than a hydrogen atom does.
 In a hydrogen chloride molecule, the shared
electrons spend more time near the chlorine atom
than near the hydrogen atom.
UNEQUAL SHARING OF ELECTRONS
Polar and Nonpolar Molecules
Can you assume that a molecule that contains a
polar covalent bond is polar?
 When a molecule has only two atoms, it will be
polar
 When molecules have more than two atoms, it
depends on the molecule
UNEQUAL SHARING OF ELECTRONS
In a carbon dioxide (CO2)
molecule, the polar bonds
between the carbon atom
and the oxygen atom cancel
out because the molecule is
linear.
In a water (H2O) molecule,
the polar bonds between the
oxygen atom and the
hydrogen atoms do not
cancel out because the
molecule is bent.
ASSESSMENT QUESTIONS
1.
What attractions hold two atoms in a molecule
together?
a.
b.
c.
d.
Attraction between ions with opposite charges
Attraction between the nuclei of the atoms and
shared electrons
Attraction between each nucleus and the electrons
of the other atom
Attraction between the molecule and other
molecules
Answer: B
ASSESSMENT QUESTIONS
2.
What determines whether a molecule is polar?
a.
b.
c.
d.
Type of atoms and shape of molecule
Mass of atoms and number of valence electrons
Type and mass of atoms
Ionization energy and number of covalent bonds
Answer: A
DESCRIBING IONIC COMPOUNDS
What information do the name and formula of an
ionic compound provide?
The name of an ionic compound must distinguish
the compound from other ionic compounds
containing the same elements.
Both of these compounds
contain copper and chlorine,
but they are not the same.
There must be two different
names to tell them apart.
DESCRIBING IONIC COMPOUNDS
What information do the name and formula of an
ionic compound provide?
The formula of an ionic compound describes the
ratio of the ions in the compound.
DESCRIBING IONIC COMPOUNDS
This table lists eight common anions. The name of
an anion is formed by adding –ide to the stem of the
name of the nonmetal.
DESCRIBING IONIC COMPOUNDS
Metals with Multiple Ions
Many transition metals form more than on type of
ion. We use Roman numerals to tell them apart.
The Roman numeral is equal to the charge on each
ion.
DESCRIBING IONIC COMPOUNDS
Polyatomic Ions
A covalently bonded group of atoms that has a
positive or negative charge and acts as a unit is a
polyatomic ion. Most simple polyatomic ions are
anions.
DESCRIBING IONIC COMPOUNDS
Writing Formulas for Ionic Compounds
Use the name of an ionic compound to write its
formula. The symbol of the cation is first,
followed by the symbol of the anion.
 Use subscripts to show the ratio of the ions in the
compound.
 Parentheses are used with the subscript for
polyatomic ions. The formula for iron(III)
hydroxide is Fe(OH)3.

DESCRIBING IONIC COMPOUNDS
Because all compounds are neutral, the total
charges on the cations and anions must add up to
zero.
Suppose an atom that gains two electrons, such as
sulfur, reacts with an atom that loses one electron,
such as sodium.
There must be two sodium ions (Na+) for each sulfide
ion (S2-).
 The formula for sodium sulfide is Na2S. The 2- charge
on one sulfide ion is balanced by the 1+ charge on two
sodium ions.

DESCRIBING IONIC COMPOUNDS
What is the formula for the ionic compound calcium
chloride?
1.
List the symbols and charges for the cation and
anion.
Ca has a charge of 2+
Cl has a charge of 1-
2.
Determine the ratio of ions in the compound.
It takes two 1- charges to balance the 2+
charge. There will be two chloride ions for
each calcium ion.
DESCRIBING IONIC COMPOUNDS
What is the formula for the ionic compound calcium
chloride?
3.
Write the formula for calcium chloride.
CaCl2
DESCRIBING IONIC COMPOUNDS
Write the formula for the compound calcium oxide.
It takes one calcium ion with a charge of 2+ to
balance out one oxygen ion with a charge of 2-. The
formula is CaO.
DESCRIBING IONIC COMPOUNDS
Write the formula for the compound copper(I)
sulfide.
It takes two copper(I) ions, each with a charge of 1+
to balance out a sulfide ion with a charge of 2-. The
formula is Cu2S.
DESCRIBING IONIC COMPOUNDS
Write the formula for the compound sodium
sulfate.
It takes two sodium ions, each with a charge of 1+
to cancel out one sulfate ion with a charge of 2-.
The formula is Na2SO4.
DESCRIBING IONIC COMPOUNDS
What is the name of the compound whose formula
is NaOH?
In the formula, Na represents the sodium ion, and
OH represents the hydroxide ion. The name of the
compound is sodium hydroxide.
DESCRIBING MOLECULAR COMPOUNDS
What information do the name and formula of a
molecular compound provide?
The name and formula of a molecular compound
describes the type and number of atoms in a
molecule of the compound.
DESCRIBING MOLECULAR COMPOUNDS
Naming Molecular Compounds
The general rule is that the element farthest to
the left appears first in the name.
 If both elements are in the same group, the
bottom-most element appears first.
 The name of the second element is changed to
end in –ide, as in carbon dioxide.

DESCRIBING MOLECULAR COMPOUNDS
There may be more than one
molecular compound that can
exist with the same two
elements.
The Greek prefixes in the table
are used to name molecular
compounds.
DESCRIBING MOLECULAR COMPOUNDS
Two compounds that contain nitrogen and oxygen
have the formulas N2O4 and NO2.
 The name of N2O4 is dinitrogen tetraoxide.
 The name of NO2 is nitrogen dioxide. The prefix
mono- is never used for the first element in the
compound.
DESCRIBING MOLECULAR COMPOUNDS
Writing Molecular Formulas
To write the formula for a molecular compounds,
write the symbols for the elements in the order the
elements appear in the name.
The prefixes indication the number of atoms of each
element in the molecule.
 The prefixes appear as subscripts in the formulas.
 If there is no prefix for an element name, there is
only one atom of that element in the molecule.

DESCRIBING MOLECULAR COMPOUNDS
What is the formula for diphosphorus
tetrafluoride?
 Phosphorus has the symbol P.
 Fluorine has the symbol F.
 Di- indicates there are two phosphorus atoms
 Tetra- indicates there are four fluorine atoms
 The formula for the compound is P2F4.
ASSESSMENT QUESTIONS
1.
Which of these formulas describes a binary ionic
compound?
a.
b.
c.
d.
O2
MgCl2
NO2
Fe(OH)3
Answer: B
ASSESSMENT QUESTIONS
2.
What is the correct name for CCl4?
a.
b.
c.
d.
Carbon(IV) chloride
Carbon tetrachlorine
Carbon tetrachloride
Monocarbon tetrachloride
Answer: C