Transcript Chapter 04

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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Ionic Molecules
►In this chapter we learn how to make ionic
molecules.
►The definition of an ionic molecule is simply a metal
with a non-metal.
►Lets see how we make ionic molecules
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Ionic Molecules
►A simple question is how many hats could fit on this
hat rack?
►Or how many cars will fit into a parking space?
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Answer:
What fits
Notice also, what
goes with what:
hat on a rack 4
►What kind of combinations can you come up with so
you end up with the right fit: same number of
positives with negatives?
1+
1+
1-
2+
2-
3+
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1-
1-
2+
1-
1+
3-
2+
3-
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Ionic Molecules
►Atoms can’t back into a parking space or hang on a
rack.
►So how does an atom “hook” into another atom?
►Atoms are small, they only have protons, neutrons
and electrons.
►Don’t forget that the protons and neutrons are
100,000 times buried inside the atom.
►It looks like the electrons, on the outside are going to
have to be our “hat rack” for other atoms.
►Lets look at these electrons more closely.
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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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Question:
Why do metals loose and why do nonmetals gain e-?
Notice whose the electrons are the hardest to
remove?
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Ionic molecules
►Elements strives to be like a noble gas
►Why---the filled shell
►Notice on the periodic table that Metals are closest to
a Noble Gas by loosing electrons.
►Nonmetals are closest to Noble Gasses if they gain
electrons.
►It’s like the parking space is happiest with only one
car or the hat rack has all the hats in it…atoms are the
same way…it’s what fits an atom.
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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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4.5 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…so they have a Filled Shell.
► 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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Learning check
►What is the electron configuration for O2-?
1s22s22p6 = [Ne]
►What is the electron configuration for Br-
[Ar]4s23d104p6
►What is the electron configuration for Al3+?
1s22s22p6 = [Ne]
►What is the electron configuration for Pb4+?
= [Xe]
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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 eliminate any common factors from
the subscripts; 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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Learning Check
►Write the correct formula for the ionic compound of
►A. H+ and CO3-2
►B. Ti+4 and C2O4-2
►C. Zn+2 and PO4-3
►D. Ca+2 and MnO4►E. Co+3 and P-3
Do NOT forget this procedure. We use this same
procedure for writing chemical equations in Chapter 6!
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Solution
►A. H2CO3
►B. Ti(C2O4)2
►C. Zn3(PO4)2
►D. Ca(MnO4)2
►E. CoP
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Learning Check
►Write the correct formula for the ionic compound of
►A. Fe+2 and NO2►B. Zr+3 and Cr2O7-2
►C. Mg+2 and SO4-2
►D. H+ and PO3-3
►E. Al+3 and HPO4-2
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Solution
►A. Fe(NO2)2
►B. Zr2(Cr2O7)3
►C. MgSO4
►D. H3PO3
►E. Al2(HPO4)3
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4.11 Naming Ionic Compounds
►There are 2 types of Molecules in Inorganic
Nomenclature
– Ionic: metal with a nonmetal
– Covalent: nonmetal with a nonmetal
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4.11 Naming Ionic Compounds
►Ionic are divided into 2 groups
– Fixed Oxidation States
– Variable Oxidation States
►Covalent compounds are divided into 2 groups
– Acids
– All others
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4.11 Naming Ionic Compounds
►See your Nomenclature lab
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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 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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End of Chapter 4
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