Chapter Four Ionic Compounds Fundamentals of General, Organic, and Biological Chemistry 5th Edition...

Chapter FourIonic Compounds

Fundamentals of General, Organic, and Biological Chemistry

5th Edition

James E. MayhughOklahoma City University2007 Prentice Hall, Inc.

Prentice Hall © 2007 Chapter Four 2

Outline

► 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

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


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?


Answer: Answer: What fitsWhat fits

Notice also, what Notice also, what goes with what: goes with what: hat on a rackhat on a rack

►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+

2+2+

3+3+

1-1-

2-2-

3-3-

1+1+ 1-1-

2+2+1-1- 1-1-

3-3-1+1+ 2+2+

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.Prentice Hall © 2007 Chapter Four 6


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.


► 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.

Question:

9

Why do metals loose and why do nonmetals gain e-?

Notice whose the electrons are the hardest to remove?

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.


► 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.


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.


4.6 Electron-Dot Symbol

Electron-dot symbol: An atomic symbol with dots placed around it to indicate the number of valence electrons.


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.


Ions formed by elements in the first four periods.

Learning check

►What is the electron configuration for O2-?

►What is the electron configuration for Br-

►What is the electron configuration for Al3+?

►What is the electron configuration for Pb4+?


1s22s22p6

[Ar]4s23d104p6

1s22s22p6 = [Ne]

= [Ne]

= [Xe]


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.


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.

20

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

22

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


►There are 2 types of Molecules in Inorganic Nomenclature– Ionic: metal with a nonmetal– Covalent: nonmetal with a nonmetal

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




►See your Nomenclature lab



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.


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.


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.


End of Chapter 4

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Chapter Four Ionic Compounds Fundamentals of General, Organic, and Biological Chemistry 5th Edition...

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