Topic
7
Table of Contents
Topic
7
Topic 7: Types of Compounds
Basic Concepts
Additional Concepts
Types of Compounds: Basic Concepts
Topic
7
Ionic Compounds
• The submicroscopic structure of ionic
compounds helps explain why they share
certain macroscopic properties such as high
melting points, brittleness, and the ability to
conduct electricity when molten or when
dissolved in water.
• You have learned that ionic compounds are
made up of oppositely charged ions held
together strongly in well-organized units.
Types of Compounds: Basic Concepts
Topic
7
Ionic Compounds
• Because of their structure, they usually are
hard solids at room temperature and are
difficult to melt. Look at the structure of
magnesium oxide.
Types of Compounds: Basic Concepts
Topic
7
Ionic Compounds
• When ionic compounds melt or dissolve in
water, their three-dimensional structure
breaks apart, and the ions are released from
the structure.
Types of Compounds: Basic Concepts
Topic
7
Ionic Compounds
• These charged ions are now free to move and
can conduct an electrical current.
Types of Compounds: Basic Concepts
Topic
7
Binary Ionic Compounds
• Formulas are part of the language that is used
to communicate information about
substances.
• As a first step in studying this new language,
you will learn how to name and write
formulas for ionic compounds.
Types of Compounds: Basic Concepts
Topic
7
Binary Ionic Compounds
• Sodium chloride (NaCl) contains only
sodium and chlorine, and potassium iodide
(KI) contains only potassium and iodine.
• Each is an example of a binary compound,
which is a compound that contains only two
elements.
Types of Compounds: Basic Concepts
Topic
7
Binary Ionic Compounds
• Binary ionic compounds can contain more
than one ion of each element, as in CaF2, but
they are not composed of three or more
different elements, as are more complex
compounds.
Types of Compounds: Basic Concepts
Topic
7
Binary Ionic Compounds
• To name a binary ionic compound, first write
the name of the positively charged ion,
usually a metal, and then add the name of the
nonmetal or negatively charged ion, whose
name has been modified to end in -ide.
• The compound formed from potassium and
chlorine is called potassium chloride.
• Magnesium combines with oxygen to form a
compound called magnesium oxide.
Types of Compounds: Basic Concepts
Topic
7
Binary Ionic Compounds
• You are already familiar with one formula for
an ionic compound—NaCl.
• Sodium chloride contains sodium ions that
have a 1+ charge and chloride ions that have
a 1– charge.
• You have learned that compounds are
electrically neutral.
Types of Compounds: Basic Concepts
Topic
7
Binary Ionic Compounds
• This means that the sum of the charges in an
ionic compound must always equal zero.
• Thus, one Na+ balances one Cl– in sodium
chloride.
Types of Compounds: Basic Concepts
Topic
7
Binary Ionic Compounds
• When you write a formula, you add
subscripts to the symbols for the ions until
the algebraic sum of the ions’ charges is zero.
• The smallest subscript to both ions that
results in a total charge of zero is 1.
• However, no subscript needs to be written
because it is understood that only one ion or
atom of an element is present if there is no
subscript.
Types of Compounds: Basic Concepts
Topic
7
Binary Ionic Compounds
• The formula NaCl indicates that sodium
chloride contains sodium and chloride ions,
that there is one sodium ion present for every
chloride ion in the compound, and that the
compound has no overall charge.
Types of Compounds: Basic Concepts
Topic
7
Binary Ionic Compounds
• If more than one ion of a given element is
present in a compound, the subscript indicates
how many ions are present.
• The mineral known as
fluorite is calcium fluoride,
which has the formula CaF2.
• This formula indicates that
there is one calcium ion for
every two fluoride ions in
the compound.
Types of Compounds: Basic Concepts
Topic
7
Binary Ionic Compounds
• In an ionic compound, a formula represents
the smallest ratio of atoms or ions in the
compound.
Types of Compounds: Basic Concepts
Topic
7
•
•
•
•
Binary Ionic Compounds
In a covalent compound, the smallest unit of
the compound is a molecule, so a formula
represents a single molecule of a compound.
This simplest ratio of ions in a compound is
called a formula unit.
Each formula unit of calcium fluoride consists
of one calcium ion and two fluoride ions.
Each of the three ions has a stable octet
configuration of electrons, and the formula
unit has no overall charge.
Types of Compounds: Basic Concepts
Topic
7
Predicting Charge on Ions
• The noble gases each have eight electrons in
their outer-energy levels.
• Metals have few outer-level electrons so they
tend to lose them and become positive ions.
• Sodium must lose just one electron, becoming
an Na+ ion.
• Calcium must lose two electrons, becoming a
Ca2+ ion.
Types of Compounds: Basic Concepts
Topic
7
Predicting Charge on Ions
• Most nonmetals, on the other hand, have
outer-energy levels that contain four to seven
electrons, so they tend to gain electrons and
become negative ions.
Types of Compounds: Basic Concepts
Topic
7
Predicting Charge on Ions
• Because all elements in a given group have
the same number of electrons in their outerenergy level, they must lose or gain the same
number of electrons to achieve a noble-gas
electron configuration.
• Metals always lose electrons and nonmetals
always gain electrons when they form ions.
• The charge on the ion is known as the
oxidation number of the atom.
Types of Compounds: Basic Concepts
Topic
7
Predicting Charge on Ions
• The oxidation numbers for many elements in
the main groups are arranged by group
number.
Types of Compounds: Basic Concepts
Topic
7
Predicting Charge on Ions
• Oxidation numbers for elements in Groups 3
through 12, the transition elements, cannot be
predicted by group number.
Types of Compounds: Basic Concepts
Topic
7
Predicting Charge on Ions
• Aluminum is in Group 13, so it loses its three
outer electrons to become an Al3+ ion;
oxygen is in Group 16 and has six valence
electrons, so it gains two electrons to become
an O2– ion.
Types of Compounds: Basic Concepts
Topic
7
Predicting Charge on Ions
• Notice that one of aluminum’s three electrons
has not been taken up by the oxygen atom.
• Because all the electrons must be accounted
for, more than one oxygen atom must be
involved in the reaction.
Types of Compounds: Basic Concepts
Topic
7
Predicting Charge on Ions
• But, oxygen cannot gain only one electron, so
a second aluminum atom must be present to
contribute a second electron to oxygen.
• In all, two Al3+ ions must combine with three
O2– ions to form Al2O3.
• Remember that the charges in the formula for
aluminum oxide must add up to zero.
Types of Compounds: Basic Concepts
Topic
7
•
•
•
•
Compounds Containing
Polyatomic Ions
The ions you have studied thus far have
contained only one element.
However, some ions contain more than one
element.
An ion that has two or more different
elements is called a polyatomic ion.
Although the individual atoms have no charge,
the group as a whole has an overall charge.
Types of Compounds: Basic Concepts
Topic
7
Compounds Containing Polyatomic Ions
Types of Compounds: Basic Concepts
Topic
7
Compounds Containing Polyatomic
Ions
Types of Compounds: Basic Concepts
Topic
Compounds Containing Polyatomic Ions
7
• Ionic compounds may contain positive metal
ions bonded to negative polyatomic ions, such
as in NaOH; negative nonmetal ions bonded to
positive polyatomic ions, such as in NH4I; or
positive polyatomic ions bonded to negative
polyatomic ions, such as in NH4NO3.
Types of Compounds: Basic Concepts
Topic
7
Compounds Containing Polyatomic
Ions
• To write the formula for an ionic compound
containing one or more polyatomic ions,
simply treat the polyatomic ion as if it were a
single-element ion by keeping it together as a
unit.
• Remember that the sum of the positive and
negative charges must equal zero.
Types of Compounds: Basic Concepts
Topic
7
Compounds Containing Polyatomic
Ions
• Multiples of a polyatomic ion in a formula
can be indicated by placing the entire
polyatomic ion, without the charge, in
parentheses.
• Write a subscript outside the parentheses to
show the number of polyatomic ions in the
compound.
• Never change the subscripts within the
polyatomic ion.
Types of Compounds: Basic Concepts
Topic
7
Compounds Containing Polyatomic
Ions
• To do so would change the composition of
the ion.
• The formula for the compound that contains
one magnesium ion and two nitrate ions is
Mg(NO3)2.
Types of Compounds: Basic Concepts
Topic
7
Compounds Containing Polyatomic
Ions
• To name a compound containing a
polyatomic ion, follow the same rules as used
in naming binary compounds.
• Name the positive ion first, followed by the
negative ion.
Types of Compounds: Basic Concepts
Topic
7
Compounds Containing Polyatomic
Ions
• However, do not change the ending of the
negative polyatomic ion name.
• The name of the compound composed of
calcium and the carbonate ion is calcium
carbonate.
Types of Compounds: Basic Concepts
Topic
7
Compounds Containing Polyatomic
Ions
• Calcium is in Group 2, so its ion has a 2+
charge. The carbonate ion has a 2– charge.
• To form a neutral compound, one Ca2+ ion
must combine with one CO32– ion to give the
formula CaCO3.
Types of Compounds: Basic Concepts
Topic
7
Compounds of Transition Elements
• Elements known as transition elements are
located in Groups 3 through 12 in the periodic
table.
• Transition elements form positive ions just as
other metals do, but most transition elements
can form more than one type of positive ion.
• In other words, transition elements can have
more than one oxidation number.
Types of Compounds: Basic Concepts
Topic
7
Compounds of Transition Elements
• For example, copper can form both Cu+ and
Cu2+ ions, and iron can form both Fe2+ and
Fe3+ ions.
• Zinc and silver are two exceptions to the
variability of other transition elements; each
forms one type of ion.
• The zinc ion is Zn2+ and the silver ion is Ag+.
Types of Compounds: Basic Concepts
Topic
7
Compounds of Transition Elements
• Chemists must have a way to distinguish the
names of compounds formed from the
different ions of a transition element.
• They do this by
using a Roman
numeral to
indicate the
oxidation number
of a transition
element ion.
Click box to view movie clip.
Types of Compounds: Basic Concepts
Topic
7
Compounds of Transition Elements
• This Roman numeral is placed in parentheses
after the name of the element.
• No additional naming system is needed for
zinc and silver compounds because their
formulas are not ambiguous.
Types of Compounds: Basic Concepts
Topic
7
Compounds of Transition Elements
Types of Compounds: Basic Concepts
Topic
7
Compounds of Transition Elements
Types of Compounds: Basic Concepts
Topic
7
Compounds of Transition Elements
Types of Compounds: Basic Concepts
Topic
7
Hydrates
• Many ionic compounds are prepared by
crystallization from a water solution, and
water molecules become a part of the crystal.
• A compound in which there is a specific ratio
of water to ionic compound is called a
hydrate.
• In a hydrate, the water molecules are
chemically bonded to the ionic compound.
Types of Compounds: Basic Concepts
Topic
7
Hydrates
• Some ionic compounds can easily become
hydrates by absorbing water molecules from
water vapor in the air.
• These compounds are called hygroscopic
substances, and one example is sodium
carbonate (Na2CO3).
• In a hydrate, the water molecules are
chemically bonded to the ionic compound.
Types of Compounds: Basic Concepts
Topic
7
Hydrates
• Substances that
are so hygroscopic
that they take up
enough water
from the air to
dissolve
completely and
form a liquid
solution are called
deliquescent.
Types of Compounds: Basic Concepts
Topic
7
Hydrates
• To write the formula for a hydrate, write the
formula for the compound and then place a
dot followed by the number of water
molecules per formula unit of compound.
• The dot in the formula represents a ratio of
compound formula units to water molecules.
• For example, CaSO4 • 2H20 is the formula for
a hydrate of calcium sulfate that contains two
molecules of water for each formula unit of
calcium sulfate.
Types of Compounds: Basic Concepts
Topic
7
Hydrates
• To name hydrates,
follow the regular
name for the
compound with the
word hydrate, to
which a prefix has
been added to
indicate the number
of water molecules
present.
Types of Compounds: Basic Concepts
Topic
7
Hydrates
• The name of the
compound with
the formula
CaSO4 • 2H2O is
calcium sulfate
dihydrate.
Types of Compounds: Basic Concepts
Topic
7
Hydrates
• Heating hydrates can drive off the water.
• This results in the formation of an anhydrous
compound—one in which all of the water has
been removed.
• In some cases, an anhydrous compound may
have different color from that of its hydrate.
Types of Compounds: Basic Concepts
Topic
7
Properties of Molecular Substances
• You know that ionic compounds share many
properties.
• The properties of a molecular substance—a
substance that has atoms held together by
covalent rather than ionic bonds—are more
variable than the properties of ionic
compounds.
Types of Compounds: Basic Concepts
Topic
7
Properties of Molecular Substances
• Molecular substances usually have lower
melting points, and most are not as hard as
ionic compounds.
• In addition, most molecular substances are
less soluble in water than ionic compounds
and are not electrolytes.
Types of Compounds: Basic Concepts
Topic
7
Properties of Molecular Substances
• A molecule that forms when atoms of the
same element bond together is called a
molecular element.
• Note that molecular elements are not
compounds—they contain atoms of only one
element.
Types of Compounds: Basic Concepts
Topic
7
Properties of Molecular Substances
• When they bond together, each atom achieves
the stability of a noble-gas electron
configuration.
• Seven nonmetal elements are found naturally
as molecular elements of two identical atoms.
Types of Compounds: Basic Concepts
Topic
7
Properties of Molecular Substances
• The elements whose natural state is
diatomic are:
• hydrogen,
• chlorine,
• nitrogen,
• bromine,
• oxygen,
• and iodine
• fluorine,
Types of Compounds: Basic Concepts
Topic
7
Properties of Molecular Substances
• Their formulas can be written as:
• H2,
• Cl2,
• N2,
• Br2,
• O2,
• and I2, respectively
• F2,
Types of Compounds: Basic Concepts
Topic
7
Properties of Molecular Substances
• If two chlorine atoms combine, they share a
single pair of electrons, and each atom attains
a stable octet configuration.
Types of Compounds: Basic Concepts
Topic
7
Properties of Molecular Substances
• Two oxygen atoms share two pairs of
electrons to form O2, and two nitrogen atoms
share three pairs of electrons to form N2.
Types of Compounds: Basic Concepts
Topic
7
Allotropes
• Although the diatomic form of oxygen, O2,
is most common in our atmosphere, oxygen
also exists as O3—ozone.
• The structure of ozone is different from that
of diatomic oxygen.
• It consists of three atoms of oxygen rather
than the two atoms in diatomic oxygen.
Types of Compounds: Basic Concepts
Topic
7
Allotropes
• Molecules of a single element that differ in
crystalline or molecular structure are called
allotropes.
Types of Compounds: Basic Concepts
Topic
7
Allotropes
• The properties of allotropes are usually
different even though they contain the same
element.
• This is because structure can be more
important than composition in determining
properties of molecules.
Types of Compounds: Basic Concepts
Topic
7
Allotropes
• Phosphorus has three
common allotropes:
white, red, and black.
• All are formed from P4
molecules that are
joined in different ways,
giving each allotrope a
unique structure and
properties.
Types of Compounds: Basic Concepts
Topic
7
Formulas and Names of Molecular
Compounds
• Chemists have devised a naming system for
molecular compounds that is based on a
much smaller number of rules than there are
compounds.
• Substances are either organic or inorganic.
Compounds that contain carbon, with a few
exceptions, are classified as organic
compounds.
Types of Compounds: Basic Concepts
Topic
7
Formulas and Names of Molecular
Compounds
• Compounds that do not contain carbon are
called inorganic compounds.
• To name these compounds, write out the
name of the first nonmetal and follow it by
the name of the second nonmetal with its
ending changed to -ide.
Types of Compounds: Basic Concepts
Topic
7
Naming Organic Compounds
• You have learned that most compounds that
contain carbon are organic compounds.
• Organic compounds make up the largest class
of molecular compounds known.
• This is because
carbon is able to
bond to other
carbon atoms in
rings and chains of
many sizes.
Types of Compounds: Basic Concepts
Topic
7
Naming Organic Compounds
• The name of even the most complex organic
compound is based on the name of a
hydrocarbon, an organic compound that
contains only the elements hydrogen and
carbon.
Basic Assessment Questions
Topic
7
Question 1
Determine the ratio of the atoms in the ionic
compound formed in each case.
A. aluminum (Al) and fluorine (F)
B. lithium (Li) and oxygen (O)
Basic Assessment Questions
Topic
7
Answers
A. aluminum (Al)
and fluorine (F)
one AL for every
three F
B. lithium (Li) and
oxygen (O)
two Li for every O
Basic Assessment Questions
Topic
7
Question 2
Write the correct formula for the ionic
compound formed between atoms of each
of the following pairs of elements.
A. sodium (Na) and sulfur (S)
B. magnesium (Mg) and nitrogen (N)
Basic Assessment Questions
Topic
7
Answers
A. sodium (Na) and sulfur (S)
Na2S
B. magnesium (Mg) and nitrogen (N)
Mg3N2
Types of Compounds: Additional Concepts
Topic
7
Additional Concepts
Types of Compounds: Additional Concepts
Topic
7
•
•
•
•
Forming Chemical Bonds
Elements tend to react so as to achieve the
stable electron configuration of a noble gas,
typically an octet of electrons.
A cation, or positive ion, is formed when an
atom loses one or more electrons.
An anion, or negative ion, is formed when an
atom gains one or more electrons.
The periodic table is useful in predicting the
charges of ions typically formed by various
atoms.
Types of Compounds: Additional Concepts
Topic
7
Properties of Ionic Compounds and
Lattice Energy
• In a solid ionic compound, the positive ions
are surrounded by negative ions, and the
negative ions by positive ions.
• The resulting structure is called a crystal
lattice and contains a regular, repeating,
three-dimensional arrangement of ions.
Types of Compounds: Additional Concepts
Topic
7
Properties of Ionic Compounds and
Lattice Energy
• This arrangement, which involves strong
attraction between oppositely charged ions,
tends almost always to produce certain
properties, such as high melting and boiling
points and brittleness.
Types of Compounds: Additional Concepts
Topic
7
Properties of Ionic Compounds and
Lattice Energy
• Ionic compounds are always nonconductors
of electricity when solid but good conductors
when melted.
• They also act as electrolytes, substances that
conduct electric current when dissolved in
water.
Types of Compounds: Additional Concepts
Topic
7
Properties of Ionic Compounds and
Lattice Energy
• The combination of these conductivity
characteristics is a very good identifier of
ionic compounds, although each characteristic
separately is not very reliable.
Types of Compounds: Additional Concepts
Topic
7
Properties of Ionic Compounds and
Lattice Energy
• The energy required to separate one mole of
the ions of an ionic compound is called lattice
energy, which is expressed as a negative
quantity.
• The greater (that is, the more negative) the
lattice energy is, the stronger is the force of
attraction between the ions.
Types of Compounds: Additional Concepts
Topic
7
Properties of Ionic Compounds and
Lattice Energy
• Lattice energy tends to be greater for morehighly-charged ions and for small ions than
for ions of lower charge or large size.
Click box to view
movie clip.
Types of Compounds: Additional Concepts
Topic
7
Naming Ionic Compounds
• Certain polyatomic ions, called oxyanions,
contain oxygen and another element.
• If two different oxyanions can be formed by
an element, the suffix -ate is used for the
oxyanion containing more oxygen atoms, and
the suffix -ite for the oxyanion containing
fewer oxygens.
• In the case of the oxyanions of the halogens,
the following special rules are used.
Types of Compounds: Additional Concepts
Topic
7
Naming Ionic Compounds
• four oxygens, per + root +-ate
(example: perchlorate, ClO4–)
• three oxygens, root + -ate
(example: chlorate, ClO3–)
• two oxygens, root + -ite
(example: chlorite, ClO2–)
• one oxygen, hypo- + root + -ite
(example: hypochlorite, ClO–)
Additional Assessment Questions
Topic
7
Questions 1
For each of the following atoms, write the
formula of the ion the atom is most likely to
form and identify that ion as a cation or an
anion.
A. bromine (Br), element 35
B. gallium (Ga), element 31
Additional Assessment Questions
Topic
7
Answers
A. bromine (Br), element 35
Br–
B. gallium (Ga), element 31
Ga3 cation
anion
Additional Assessment Questions
Topic
7
Question 2
Name the ionic Compounds that have the
following formulas.
A. Mg(NO3)2
B. KHSO4
Additional Assessment Questions
Topic
7
Answers
A. Mg(NO3)2
magnesium nitrate
B. KHSO4
potassium hydrogen sulfate
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