Fundamentals of General, Organic,
and Biological Chemistry
5th Edition
Chapter Four
Ionic Compounds
James E. Mayhugh
Oklahoma City University
2007 Prentice Hall, Inc.
Outline
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4.1 Ions
4.2 Periodic Properties and Ion Formation
4.3 Ionic Bonds
4.4 Some Properties of Ionic Compounds
4.5 Ions and the Octet Rule
4.6 Electron-Dot Symbols
4.7 Ions of Some Common Elements
4.8 Naming Ions
4.9 Polyatomic Ions
4.10 Formulas of Ionic Compounds
4.11 Naming Ionic Compounds
4.12 H+ and OH- Ions: An Introduction to Acids and Bases
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4.1 Ions
► Atoms are electrically neutral because they contain
equal numbers of protons and electrons.
► By gaining or losing one or more electrons,
however, an atom can be converted into a charged
particle called an ion.
► The symbol for an ion is written by adding the
electrical charge as a superscript to the symbol for
the element.
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► The loss of one or more electrons from a neutral
atom gives a positively charged ion called a cation.
► Sodium and other alkali metal atoms have a single
electron in their valence shell.
► By losing this electron, an alkali metal is converted
to a cation with a full valence shell.
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► The gain of one or more electrons by a neutral atom
gives a negatively charged ion called an anion.
► Chlorine and other halogens have 7 valence
electrons.
► Halogens easily gain an additional electron to fill out
their valence subshell to form anions.
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4.2 Periodic Properties and Ion
Formation
► Ionization energy: The energy required to remove
one electron from a single atom in the gaseous state.
► Low ionization energies (IE) favor cation formation.
► Electron affinity: The energy released on adding an
electron to a single atom in the gaseous state.
► High electron affinities (EA) favor anion formation.
► Going from left to right on the periodic table, IE and
EA values both increase.
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► Ionization energies (red) and electron affinities
(blue) for the first 36 elements.
► Alkali metals have the lowest ionization energies and
lose an electron most easily.
► Halogens have the highest electron affinities and
gain an electron most easily.
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► The noble gases neither gain nor lose an electron
easily. They have high IE values and low EA values.
► Main group elements near the middle of the periodic
table have intermediate values of both IE and EA.
► These elements near group 4A lack a strong
preference to either lose or gain electrons.
► Later we will see that these elements tend not to
form ionic bonds but form covalent bonds instead.
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4.3 Ionic Bonds
When sodium metal reacts with chlorine gas crystals of
sodium chloride or table salt are formed.
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► In a violent reaction, sodium atoms transfer electrons
to chlorine atoms forming Na+ ions and Cl- ions.
► The opposite electrical charges attract each other.
Crystals of sodium chloride held together by ionic
bonds result that are unlike either of the elements
from which they are formed.
► Ionic bond: The electrical attractions between ions
of opposite charge in a crystal.
► Ionic compound: A compound that contains ionic
bonds.
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Na+ and Cl- ions in a sodium chloride crystal.
►Each Na+ ion is
surrounded by six
Cl- ions, and each
Cl- ion is
surrounded by six
Na+ ions.
►The crystal is held
together by ionic
bonds—the
attraction between
oppositely charged
ions.
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4.4 Some Properties of Ionic
Compounds
► Ionic compounds are usually crystalline solids.
► Ions in an ionic solid are held rigidly in place by
attraction to their neighbors and cannot move about.
► Once an ionic solid is dissolved in water or melted,
the ions can move freely and conduct electricity.
► High melting points and boiling points are observed
for ionic compounds because the attractive forces are
extremely strong.
► Sodium chloride melts at 801ºC and boils at 1413ºC.
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► Ionic solids are not malleable and will shatter if
struck sharply.
► Ionic compounds dissolve in water if the attraction
between water and the ions overcomes the attraction
of the ions for one another.
► Sodium chloride and some other familiar ionic
compounds are very soluble and can be dissolved to
make solutions of high concentration.
► Other ionic compounds are not water-soluble,
because water is unable to overcome the ionic forces
in many crystals.
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4.5 Ions and the Octet Rule
► Main group elements often combine in such a way
that each winds up with an electron configuration
like a noble gas. Usually 8 valence electrons or an
electron octet.
► Octet rule: Main group elements tend to undergo
reactions that leave them with 8 valence electrons.
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4.6 Electron-Dot Symbol
Electron-dot symbol: An atomic symbol with dots
placed around it to indicate the number of valence
electrons.
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4.7 Ions of Some Common Elements
► Ionic charges of main group elements can be
predicted using the group number and the octet rule.
► For 1A, 2A, and 3A metals, charge = group number
► For nonmetals in groups 5A, 6A, and 7A, anion
charge = (group number) - 8.
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Ions formed by elements in the first four periods.
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4.8 Naming Ions
Main group metal cations in group 1A, 2A, and 3A are
named by identifying the metal, followed by the word
“ion” as shown below:
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K+
Potassium ion
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Mg2+ Magnesium ion
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Al3+ Aluminum ion
For transition metals which can form more than one
type of cation, two systems are used.
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► In the old system, the ion with the smaller charge ends in -ous
and the ion with the larger charge ends in -ic.
► The new system uses Roman numerals to indicate the charge
on the ion.
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► Anions are named by replacing the ending of the
element name with -ide, followed by the word “ion.”
► For example, the anion formed by fluorine is the
fluoride ion, and the anion formed by sulfur is the
sulfide ion.
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4.9 Polyatomic Ions
► Ions that are composed of more than one atom are
called polyatomic ions.
► Most polyatomic ions contain oxygen and another
element, and their chemical formulas show by
subscripts how many of each type of atom are
combined.
► Sulfate ion, for example, is composed of one sulfur
atom and four oxygen atoms, and has a charge of -2;
the entire group of atoms acts as a single unit.
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4.10 Formulas of Ionic Compounds
► A chemical formula shows the simplest ratio of
anions and cations required for a total charge of zero.
► A shortcut is to make the subscript of each ion equal
to the charge on the other ion.
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Once the numbers and kinds of ions in a
compound are known, the formula is written using
the following rules:
►List the cation first and the anion second; for
example, NaCl not ClNa.
►Make sure to reduce to the simplest formula; for
example, MgO not Mg2O2.
►Do not write the charges of the ions; for example, KF
not K+F►Use parentheses around a polyatomic ion formula if it
has a subscript; for example, Al2(SO4)3 not Al2SO43.
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Active Ingredient in Bleach
Sodium hypochlorite
Na+ + OCl-
NaOCl
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Smelling Salts
Ammonium carbonate
2 NH4+ + 1 CO3-2
Charge = +2
Charge = -2
(NH4)2CO3
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4.11 Naming Ionic Compounds
► Compounds are named by citing first the cation
and then the anion, with a space between words.
► For example, MgSO4 is called magnesium sulfate.
► Name these:
CaCO3
K2SO4
Li3PO4
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2 Different Cations of the Same
Metal
► Some transition metals form more than one cation.
Fe+2 and Fe+3
Cu+ and Cu+2
Sn+2 and Sn+4
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Naming Ionic Compounds
► We need to specify the charge on the cation in the
names of these compounds.
► The old and new ways to do this are shown in the
examples below:
SnCl2 - Stannous chloride or Tin (II) chloride
SnCl4 - Stannic chloride or Tin (IV) chloride
FeO – Ferrous oxide or Iron (II) oxide
Fe2O3 – Ferric oxide or Iron (III) oxide
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Name These…
►AuCl3
►Cu2CO3
►Ba(OH)2
►SnO2
►Fe2(SO4)3
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►AuCl3
►Cu2CO3
►Ba(OH)2
►SnO2
►Fe2(SO4)3
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Gold(III) chloride
Copper(I) carbonate
Barium hydroxide
Tin(IV) oxide
Iron (III) sulfate
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4.12 H+ and OH- Ions: An
Introduction to Acids and Bases
►The importance of the H+ cation and the OH- anion is
that they are fundamental to the concepts of acids and
bases.
►Acid: A substance that provides H+ ions in water; for
example, HCl  H+ + Cl►Base: A substance that provides OH- ions in water;
for example, NaOH  Na+ + OH-
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Acids Dissociate into H+ ions
H2SO 4
+
H +
HSO4
H3PO4
+
H2PO4
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H +
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Chapter Summary
► Atoms are converted into cations by the loss of one
or more electrons and into anions by the gain of one
or more electrons.
► Ionic compounds are composed of cations and
anions held together by ionic bonds. Ionic
compounds conduct electricity when dissolved in
water, and they are generally crystalline solids with
high melting points and very high boiling points.
► Main group elements tend to form ions in which they
have gained or lost the appropriate number of
electrons to reach a noble gas configuration.
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Chapter Summary Cont.
► Metals lose electrons more easily than nonmetals.
As a result, metals usually form cations.
► Nonmetals gain electrons more easily than metals.
As a result, reactive nonmetals usually form anions.
► The ionic charge can be predicted from the
group number and the octet rule. For main group
metals, the charge on the cation is equal to the
group number. For nonmetals, the charge on the
anion is equal to the group number - 8.
► Ionic compounds contain appropriate numbers of
anions and cations to maintain overall neutrality.
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Chapter Summary Cont.
► Cations have the same name as the metal,
monatomic anions have the name ending -ide.
► For metals that form more than one ion, a Roman
numeral equal to the charge is used to name the ion.
► The cation name is given first, with the charge of
the metal ion indicated if necessary, and the anion
name is given second.
► An acid is a substance that yields H+ ions when
dissolved in water, and a base is a substance that
yields OH- ions when dissolved in water.
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