Topic
6
Table of Contents
Topic
6
Topic 6: Formation of Compounds
Basic Concepts
Additional Concepts
Formation of Compounds: Basic Concepts
Topic
6
Salt: A Familiar Compound
• Sodium chloride occurs naturally in large,
solid, underground deposits throughout the
world and is dissolved in the world’s oceans.
• Salt can be
obtained by
mining these
solid deposits,
and by the
evaporation of
seawater.
Formation of Compounds: Basic Concepts
Topic
6
•
•
•
•
Physical Properties of Salt
Table salt is a white solid at room
temperature.
If sodium chloride is heated to a temperature
of about 800°C, it melts and forms liquid salt.
Solid sodium chloride does not conduct
electricity, but melted sodium chloride does.
Salt also dissolves easily in water. The
resulting solution is an excellent conductor
of electricity.
Formation of Compounds: Basic Concepts
Topic
6
Chemical Properties of Salt
• Salt does not react
readily with other
substances.
Properties of Sodium
• Sodium is a shiny,
silvery-white, soft,
solid element.
Formation of Compounds: Basic Concepts
Topic
6
Properties of Sodium
• Sodium melts to form a liquid when it is
heated above 98°C.
• Sodium must be stored under oil because it
reacts with oxygen and water vapor in the air.
• Because of its high reactivity, the free
element sodium is never found in the
environment.
Formation of Compounds: Basic Concepts
Topic
6
Properties of Chlorine
• The element chlorine, is a pale green,
poisonous gas with a choking odor.
• Like sodium, it is among the most reactive
of the elements and must be handled with
extreme care.
• Because chlorine is slightly soluble in
water, it is an excellent disinfectant for
swimming pools.
Formation of Compounds: Basic Concepts
Topic
6
Composition of Inhaled
and Exhaled Air
• The mixture of gases that you exhale contains
more than 100 times the amount of carbon
dioxide that was in the air that you inhaled.
Formation of Compounds: Basic Concepts
Topic
6
Physical Properties of Carbon Dioxide
• Carbon dioxide is a colorless, odorless, and
tasteless gas.
• When carbon dioxide is cooled below
280°C, the gas changes directly to white,
solid carbon dioxide without first becoming
a liquid.
Formation of Compounds: Basic Concepts
Topic
6
Physical Properties of Carbon Dioxide
• Because the solid
form of carbon
dioxide does not
melt to a liquid, it
is called dry ice.
Formation of Compounds: Basic Concepts
Topic
6
The Properties of Carbon
• Carbon is a nonmetal and is fairly unreactive
at room temperature.
• However, at higher temperatures, it reacts
with many other elements.
• The majority of compounds that make up
living things contain carbon.
Formation of Compounds: Basic Concepts
Topic
6
•
•
•
•
The Properties of Oxygen
Oxygen is another nonmetal. It is a colorless,
odorless, and tasteless gas that makes up
about 21 percent of the air you breathe.
Oxygen gas becomes a liquid when it is
cooled to –183°C, and it is slightly soluble
in water.
Oxygen is more reactive than carbon.
A prime example of its reactivity is the
process of rusting, in which the element
iron combines with oxygen from air.
Formation of Compounds: Basic Concepts
Topic
6
Elemental Composition of Earth’s Crust
• Referring to the
circle graph, one
can see that oxygen
is the most
abundant element
in Earth’s crust.
• Nearly all of this
oxygen occurs in
compounds with
other elements.
Formation of Compounds: Basic Concepts
Topic
6
Physical Properties of Water
• Water covers approximately 70 percent
of Earth’s surface and also makes up about
70 percent of the mass of the average
human body.
• Water is the only one of the three
compounds that occurs in Earth’s
environment in all three states of matter.
Formation of Compounds: Basic Concepts
Topic
6
Physical Properties of Water
• Liquid water boils into gaseous water
(steam) at 100°C and freezes to solid
water (ice) at 0°C.
• It is often called the universal solvent in
recognition of this valuable property.
Formation of Compounds: Basic Concepts
Topic
6
Chemical Properties of Water
• Water is a stable compound, and acts as a
medium in which chemical reactions occur.
Formation of Compounds: Basic Concepts
Topic
6
•
•
•
•
•
•
The Properties of Hydrogen
Hydrogen is the lightest and most abundant
element in the universe.
Hydrogen is usually classified as a nonmetal.
Hydrogen is a reactive element.
It occurs in a variety of compounds,
particularly water.
Hydrogen reacts vigorously with many
elements, including oxygen.
Hydrogen does not conduct electricity and is
only slightly soluble in water.
Formation of Compounds: Basic Concepts
Topic
6
Chemical Reactions
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Formation of Compounds: Basic Concepts
Topic
6
The Octet Rule
• Noble gases are unlike any other group of
elements on the periodic table because of
their extreme stability.
• Each noble gas has eight valence electrons,
except for helium, which has two.
Formation of Compounds: Basic Concepts
Topic
6
The Octet Rule
• The modern model of how atoms react to
form compounds is based on the fact that
the stability of a noble gas results from the
arrangement of its valence electrons.
• This model of chemical stability is called
the octet rule.
Formation of Compounds: Basic Concepts
Topic
6
The Octet Rule
• The octet rule says
that atoms can
become stable by
having eight electrons
in their outer energy
level, as shown in the
noble gas, Neon, (or
two electrons in the
case of some of the
smallest atoms).
Formation of Compounds: Basic Concepts
Topic
6
The Octet Rule
• Elements become stable by achieving the
same configuration of valence electrons as
one of the noble gases, a noble gas
configuration.
Click box to view
movie clip.
Formation of Compounds: Basic Concepts
Topic
6
Electrons Can Be Transferred
• Sodium is in Group 1, so it has one valence
electron.
• Chlorine is in Group 17 and has seven
valence electrons.
Formation of Compounds: Basic Concepts
Topic
6
Electrons Can Be Transferred
• How can the valence electrons of atoms
rearrange to give each atom a stable
configuration of valence electrons?
• If the one valence electron of sodium is
transferred to the chlorine atom, chlorine
becomes stable with an octet of electrons.
Formation of Compounds: Basic Concepts
Topic
6
Electrons Can Be Transferred
• Because the chlorine atom now has an extra
electron, it has a negative charge.
• Also, because sodium lost an electron, it
now has an unbalanced proton in the
nucleus and therefore has a positive charge.
Formation of Compounds: Basic Concepts
Topic
6
Electrons Can Be Transferred
• Now that each atom has an octet of outerlevel electrons, they are no longer neutral
atoms; they are charged particles called ions.
• An ion is an atom or group of combined
atoms that has a charge because of the loss or
gain of electrons.
Formation of Compounds: Basic Concepts
Topic
6
Electrons Can Be Transferred
• A compound that is composed of ions is
called an ionic compound.
• Note that only the
arrangement of
electrons has
changed. Nothing
about the atom’s
nucleus has
changed.
Click box to view movie clip.
Formation of Compounds: Basic Concepts
Topic
6
Formation of an Ionic Compound
• Remember that objects with opposite charges
attract each other.
• The strong attractive force between ions of
opposite charge is called an ionic bond.
• The force of the ionic bond holds ions
together in an ionic compound.
Formation of Compounds: Basic Concepts
Topic
6
Formation of an Ionic Compound
• Unprotected aluminum metal reacts with
oxygen in air, forming the white coating
you can observe on aluminum objects such
as lawn furniture.
• Explain the formation of an ionic compound
from the elements aluminum and oxygen.
Formation of Compounds: Basic Concepts
Topic
6
Formation of an Ionic Compound
1. Analyze the Problem
• You are given that aluminum and oxygen
react to form an ionic compound.
• Aluminum is a group 3A element with three
valence electrons, and oxygen is a group 6A
element with six valence electrons.
• To acquire a noble gas configuration, each
aluminum atom must lose three electrons
and each oxygen atom must gain two
electrons.
Formation of Compounds: Basic Concepts
Topic
6
Formation of an Ionic Compound
2. Solve for the Unknown
• Remember that the number of electrons
lost must equal the number of electrons
gained.
• The smallest number evenly divisible by
the three electrons lost by aluminum and
the two gained by oxygen is six.
• Three oxygen atoms are needed to gain the
six electrons lost by two aluminum atoms.
Formation of Compounds: Basic Concepts
Topic
6
Formation of an Ionic Compound
3. Evaluate the Answer
• The overall charge on one unit of this
compound is zero.
Formation of Compounds: Basic Concepts
Topic
6
Formation of Water by Electron
Sharing
• The stability of the atoms in a water molecule
results from a cooperative arrangement in
which the eight valence electrons (six from
oxygen and one each from two hydrogens)
are distributed among the three atoms.
Formation of Compounds: Basic Concepts
Topic
6
Formation of Water by Electron
Sharing
• By sharing an electron pair with the oxygen,
each hydrogen claims two electrons in its
outer level.
Formation of Compounds: Basic Concepts
Topic
6
Formation of Water by Electron
Sharing
• The oxygen, by sharing two electrons with
two hydrogens, claims a stable octet in its
outer level.
• By this method, each atom achieves a stable
noble gas configuration.
Formation of Compounds: Basic Concepts
Topic
6
Electron Sharing Produces Molecules
• The attraction of two atoms for a shared
pair of electrons is called a covalent bond.
• Notice that in a
covalent bond,
atoms share
electrons and
neither atom has
an ionic charge.
Click box to view movie clip.
Formation of Compounds: Basic Concepts
Topic
6
Electron Sharing Produces Molecules
• A compound whose atoms are held together
by covalent bonds is a covalent compound.
• Water is a covalent compound.
Formation of Compounds: Basic Concepts
Topic
6
Electron Sharing Produces Molecules
• A molecule is an
uncharged group of
two or more atoms
held together by
covalent bonds.
• Ethanol, also
known as ethyl
alcohol, is a
typical covalent
compound.
Formation of Compounds: Basic Concepts
Topic
6
Explaining the Properties
of Ionic Compounds
• Ionic compounds are
composed of well-organized,
tightly bound ions.
• These ions form a strong,
three-dimensional crystal
structure.
• Ionic compounds are
crystalline solids at
room temperature.
Formation of Compounds: Basic Concepts
Topic
6
Explaining the Properties
of Ionic Compounds
• Ionic compounds usually have to be heated
to high temperatures in order to melt them
because the attractions between ions of
opposite charge are strong.
Formation of Compounds: Basic Concepts
Topic
6
Electrolytes
• Another physical property of ionic
compounds is their tendency to dissolve
in water and conduct electricity in the
liquid (melted) state.
• Any compound that conducts electricity
when melted or dissolved in water is an
electrolyte.
• In order to conduct electricity, ions must
be free to move because they must take on
or give up electrons.
Basic Assessment Questions
Topic
6
Question 1
What is the difference between sodium
and chlorine?
Answer
Sodium is a metal that can be cut with a knife
and has a silvery luster where it has been cut.
Chlorine is a pale green, poisonous gas that
kills living cells.
Basic Assessment Questions
Topic
6
Question 2
How many valence electrons must an atom
have in its outer energy level in order to be
considered stable?
Answer
The answer is 8.
Basic Assessment Questions
Topic
6
Question 3
Do atoms that share a covalent bond have an
ionic charge?
Answer
No, the atoms share electrons and neither
atom has a charge.
Formation of Compounds: Additional Concepts
Topic
6
Additional Concepts
Formation of Compounds: Additional Concepts
Topic
6
Forming Chemical Bonds
• When energy is added to or taken away from
a system, one phase can change into another.
• The force that holds two atoms together is
called a chemical bond.
• Chemical bonds form because of attractions
between oppositely charged atoms, called
ions, or between electrons and nuclei.
Formation of Compounds: Additional Concepts
Topic
6
Forming Chemical Bonds
• 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.
Formation of Compounds: Additional Concepts
Topic
6
Determining Charges of Ions
• To determine the electron configuration, refer
to the periodic table.
• Write the formula of the ion the atom is most
likely to form.
• Next, identify that ion as a cation or an anion.
• Finally, write the electron configuration of
the ion.
Formation of Compounds: Additional Concepts
Topic
6
Determining Charges of Ions
• For example:
• bromine (Br), element 35
• (neutral Br: 1s22s22p63s23p64s23d104p5; ion:
–
Br , anion 1s22s22p63s23p64s23d104p6)
Formation of Compounds: Additional Concepts
Topic
6
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.
Formation of Compounds: Additional Concepts
Topic
6
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.
Formation of Compounds: Additional Concepts
Topic
6
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.
Formation of Compounds: Additional Concepts
Topic
6
Properties of ionic compounds
and lattice energy
• Based on the properties of the following
“unknowns,” each is classified as either
ionic or not ionic.
Ionic
Not Ionic
has a high boiling point and
shatters when hammered
conducts electricity when liquid
and has a low melting point
has a high melting point and
conducts electricity when
dissolved in water
conducts electricity when solid
Formation of Compounds: Additional Concepts
Topic
6
Properties of ionic compounds
and lattice energy
• Between each of the following pairs of
ionic compounds, only one would be
expected to have the higher (more negative)
lattice energy.
1. LiF or KBr (LiF would have the higher
lattice energy)
2. NaCl or MgS (MgS would have the higher
lattice energy)
Formation of Compounds: Additional Concepts
Topic
6
Names and Formulas
for Ionic Compounds
• The simplest ratio of the ions represented in
an ionic compound is called a formula unit.
• The overall charge of any formula unit is
zero.
• In order to write a correct formula unit, one
must know the charge of each ion.
Formation of Compounds: Additional Concepts
Topic
6
Names and Formulas
for Ionic Compounds
• The charges of monatomic ions, or ions
containing only one atom, can often be
determined by referring to the periodic table
or table of
common
ions
based on
group
number.
Formation of Compounds: Additional Concepts
Topic
6
Names and Formulas
for Ionic Compounds
• For example, ions of group 1A typically
have a charge of 1+.
• Those of group 2A have a charge of 2+.
• Those of group 7A have a charge of 1–.
Formation of Compounds: Additional Concepts
Topic
6
Names and Formulas
for Ionic Compounds
• The charge of a monatomic ion is equal to
its oxidation number.
• The oxidation number, or oxidation state, of
an ion in an ionic compound is numerically
equal to the number of electrons that were
transferred to or from an atom of the
element in forming the compound.
Formation of Compounds: Additional Concepts
Topic
6
Oxidation Numbers
• Oxidation numbers can be used to determine
the chemical formulas for ionic compounds.
• If the oxidation number of each ion is
multiplied by the number of that ion present
in a formula unit, and then the results are
added, the sum must be zero.
Formation of Compounds: Additional Concepts
Topic
6
Oxidation Numbers
• In the formula for an ionic compound, the
symbol of the cation is written before that
of the anion.
• Subscripts, or small numbers written to the
lower right of the chemical symbols, show
the numbers of ions of each type present in
a formula unit.
Formation of Compounds: Additional Concepts
Topic
6
•
•
•
•
•
Naming ionic compounds
In naming ionic compounds, name the cation
first, then the anion.
Monatomic cations use the element name.
Monatomic anions use the root of the
element name plus the suffix -ide.
If an element can have more than one
oxidation number, use a Roman numeral in
parentheses after the element name, for
example, iron(II) to indicate the Fe2+ ion.
For polyatomic ions, use the name of the ion.
Formation of Compounds: Additional Concepts
Topic
6
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.
Formation of Compounds: Additional Concepts
Topic
6
Naming ionic compounds
• four oxygens,
per + root + ate (example:
perchlorate,
ClO4–)
• three oxygens,
root + -ate
(example:
chlorate, ClO3–)
Formation of Compounds: Additional Concepts
Topic
6
Naming ionic compounds
• two oxygens,
root + -ite
(example:
chlorite, ClO2–)
• one oxygen,
hypo- + root +
-ite (example:
hypochlorite,
–
ClO )
Formation of Compounds: Additional Concepts
Topic
6
Naming ionic compounds
• The formulas below are followed by their
ionic compound.
1. NaBrO3
(sodium bromate)
2. Mg(NO3)2
(magnesium nitrate)
3. NH4ClO4
(ammonium perchlorate)
4. Al(ClO)3
(aluminum hypochlorite)
Formation of Compounds: Additional Concepts
Topic
6
Metallic Bonds and Properties of Metals
• The bonding in metals is explained by the
electron sea model, which proposes that
the atoms in a metallic solid contribute
their valence electrons to form a “sea” of
electrons that surrounds metallic cations.
• These delocalized electrons are not held
by any specific atom and can move easily
throughout the solid.
• A metallic bond is the attraction between
these electrons and a metallic cation.
Formation of Compounds: Additional Concepts
Topic
6
Metallic Bonds and Properties of Metals
• Metals generally have extremely high boiling
points because it is difficult to pull metal
atoms completely
away from the group
of cations and
attracting electrons.
Formation of Compounds: Additional Concepts
Topic
6
Metallic Bonds and Properties of Metals
• Metals are also malleable (able to be
hammered into sheets) and ductile (able to be
drawn into wire)
because of the
mobility of the
particles.
• The delocalized
electrons make metals
good conductors of
electricity.
Formation of Compounds: Additional Concepts
Topic
6
Metallic Bonds and Properties of Metals
• A mixture of elements that has metallic
properties is called an alloy.
• Alloys can be of two basic types.
• A substitutional alloy is one in which atoms
of the original metal are replaced by other
atoms of similar size.
• An interstitial alloy is one in which the
small holes in a metallic crystal are filled by
other smaller atoms.
Additional Assessment Questions
Topic
6
Question 1
What is the electron configuration, in
abbreviated form, for nickel?
Answer
[Ar]4s23d8
Additional Assessment Questions
Topic
6
Question 2
What structure has positive ions surrounded by
negative ions, and the negative ions surrounded
by positive ions?
Answer
a crystal lattice
Additional Assessment Questions
Topic
6
Question 3
What is the correct formula for the ionic
compound aluminum sulfate?
Answer
Al2(SO4)3
Practice Problems
Topic
6
Question 1
Determine the correct formula for the ionic
compound composed of the following pairs
of ions.
Practice Problems
Topic
6
Question 1a
aluminum and carbonate
Answer 1a
Al2(CO3)3
Practice Problems
Topic
6
Question 1b
magnesium and carbonate
Answer 1b
MgCO3
Practice Problems
Topic
6
Question 1c
calcium and chlorate
Answer 1c
Ca(ClO3)2
Practice Problems
Topic
6
Question 2
Name the following compounds.
Practice Problems
Topic
6
Question 2a
Co(OH)2
Answer 2a
cobalt hydroxide
Practice Problems
Topic
6
Question 2b
Ag2CrO4
Answer 2b
silver chromate
Practice Problems
Topic
6
Question 2c
Na3PO4
Answer 2c
sodium phosphate
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