Chapter 3Ionic Compounds

The joining of two atoms in a stable arrangement

Elements gain, lose, or share electrons to reach the electron configuration of the noble gas closest to them in the periodic table

Two types of bonding◦ Ionic bonds: result from the transfer of electrons

from one element to another◦ Covalent bonds: result from the sharing of

electrons between two atoms

Bonding

A pure substance that cannot be broken down into simpler substances by a chemical reaction

Identified by a one- or two-letter symbol Arranged in the periodic table Its location on the periodic table indicates a

lot about its chemical properties Can be a metal, nonmetal, or a metalloid

Elements

Ionic bonds

Ionic bonds Ionic bonds

◦ Form between a metal (left side of periodic table) and a nonmetal (right side of periodic table

Covalent bonds◦ Form when two nonmetals combine ◦ Form when a metalloid bonds to a nonmetal

Periodic Table

Positively charged ions Have fewer elections (e-) than protons

sodium atom sodium ion

Cations

Negatively charged ions Has more e- than protons

◦ chlorine atom chlorine ion

Anions

A main group element is especially stable when it possesses an octet of e- in its outer shell

Octet rule

octet = 8 valence e−

Charge based on periodic group

group 1A:

group 2A:

group 3A:

M1 valence e−

M+ + e−

M2 valence e−

M2+ + 2e−

M3 valence e−

M3+ + 3e−

the cation charge = the group number

Charge based on periodic group

group 6A: X6 valence e−

+ 2e− X 2−

group 7A: X7 valence e−

+ e− X −

the anion charge = 8 – group number

charge = 8 – 6 = 2

charge = 8 – 7 = 1

Main Group Ions

Metals with variable charges

Biologically relevant ions

The sum of the charges in an ionic compound must be zero overall

Ions will arrange to maximize anion-cation attractions and minimize anion-anion and cation-cation repulsions

Ionic compounds

There must be two F- anions for each Ca+ cation to have an overall charge of zero

Ion compounds – charge balance

Formula for ionic compounds

HOW TO Write a Formula for an Ionic Compound

Step [1]

Identify which element is the cationand which is the anion.

Step [2]

Determine how many of each ion type is needed for an overall charge of zero. When the cation and anion have different

charges, use the ion charges to determine the number of ions of each needed.

Step [3]

To write the formula, place the cationfirst and then the anion, and omit charges.

Calcium Iodide◦ Cation = calcium

Charge 2+◦ Anion = iodine

Charge -◦ Need two iodine for every calcium for an overall

charge of zero◦ CaI2

Example

Ionic comound criss-cross rule

“Criss-cross” rule Make magnitude of charge on one ion into

subscript for other When doing this, make sure that subscripts are

reduced to lowest whole number.

Al2O3Al3+ O2–

Main group cations

Main group cations are named for the element from which they are formed.

Na+ K+ Ca2+ Mg2+

sodium potassium calcium magnesium

Systematic name◦ Follow the name of the cation by a Roman

numeral in parentheses to indicate its charge

Common name◦ Use suffic “-ous” for the cation with a smaller

charge and suffix “-ic” for the cation with a higher charge

Multiple charge cations

Fe2+

iron(II)Fe3+

iron(III)

ferrous ferricFe2+ Fe3+

Anions are named by replacing the ending of the element name by the suffix “-ide.”

Anions

Name the cation and then the anion Do not specify the charge on the ion Do not specify how many ions of each type

are needed to balance charge

Naming ionic compounds

Na+

sodiumF−

fluorideNaF

sodium fluoride+

Mg2+

magnesiumCl−

chlorideMgCl2

magnesium chloride+

Naming ionc compoundsHOW TO Name an Ionic

CompoundStep [1] Determine the charge on the cation.

Step [2] Name the cation and the anion

If the cation could be multiple charges indicate the charge with roman numerals or with a –ous / -ic suffix.

Step [3]

Write the name of the cation first then the name of the anion

K2O◦ Cation = K+

◦ Anion = O2-

◦ Potassium Oxide LiBr

◦ Cation = Li+

◦ Anion = Br-

◦ Lithium Bromide SnO

◦ Cation = Sn2+

◦ Anion = O2-

◦ Tin (II) Oxide /Stannous Oxide

Examples

Naming ionic compoundsHOW TO Derive the Formula from the Name of

an Ionic Compound

Step [1] Identify the cation and the anion.

Step [2] Determine the charge on the cation and anion.

Step [3]

Balance the charges.

Step [4]

Write the formula with the cation first and use subscripts to communicate charge balance.

Cobalt (II) Oxide/Cobaltous Oxide◦ Cation = Co 2+

◦ Anion = O2-

◦ CoO Iron(III) Fluoride/Ferric Flouride

◦ Cation = Fe3+

◦ Anion = F-

◦ FeF3

Beryllium Chloride◦ Cation = Be2+

◦ Anion = Cl-

◦ BeCl2

Examples

Ionic compounds are crystalline solids with very high melting and boiling points

When ionic compounds dissolve in water, they separate into cations and anions, increasing the conductivity of the solution

Physical properties of ionic compounds

NaCl

+

water solution

A cation or anion that contains more than one atom

The multiple atoms are held together with covalent bonds

The molecule has an overall charge associated with it

Polyatomic ions

When a cation and anion of equal charge combine, only one of each ion is needed

Formulas for polyatomic ions

Na+ NO2−+ NaNO2

zero overallcharge

Ba2+ SO42−+ BaSO4

zero overallcharge

When a cation and anion of unequal charge combine, use the ionic charges to determine the relative number of each ion that is needed

Formulas for polyatomic ions

Mg2+ OH−+ Mg(OH)2

zero overallcharge

+2 charge means2 OH− anions are

needed.

−1 charge means1 Mg2+ anion is

needed.

The same rules are followed for naming standard ionic compounds:

• Name the cation and then the anion.• Do not specify the charge on the ions.• Do not specify how many ions of each type

are needed to balance charge.•Use –ite suffix if 1 or less Oxygen atoms in anion•Use –ate suffix if more Oxygen atoms in anion•Use bi- prefix or write hydrogen if H part of anion

Naming polyatomic ionic compounds

NaHCO3 Al2(SO4)3

sodium bicarbonate aluminum sulfate