CHAPTER 7

IONIC COMPOUNDS AND METALS

CHEMICAL BOND A CHEMICAL BOND IS A FORCE THAT

HOLDS TWO ATOMS TOGETHER. CAN FORM BETWEEN THE POSITIVE

NUCLEUS OF ONE ATOM AND THE NEGATIVE ELECTRONS OF ANOTHER, OR BY THE ATTRACTION OF POSITIVE AND NEGATIVE IONS.

WE WILL DISCUSS THE ATTRACTIONOF POSITIVE AND NEGATIVE IONS IN THIS CHAPTER.

VALENCE ELECTRONS The outermost electrons that are involved in

chemical bonding. Know these groups and their number of valence

electrons:Group 1 = 1Group 2 = 2Group 13 = 3Group 14 = 4Group 15 = 5Group 16 = 6Group 17 = 7Group 18 = 8NOTE: We will discuss the transition metals later

ELECTRON CONFIGURATION AND VALENCE ELECTRONShttp://periodic.lanl.gov/images/periodictable.pdf

ELECTRON DOT DIAGRAM Diagram used to keep track of valence

electrons. Examples:

POSITIVE ION FORMATION A positive ion forms when an atom loses

one or more valence electrons in order to attain a noble gas configuration.

Noble gases are stable because they have 8 valence electrons (with the exception of helium)

A positive ion is known as a cation In an ionic bond metals lose electrons to

become stable. Therefore, groups 1, 2 , and 3-13 lose electrons during chemical bonding

NEGATIVE ION FORMATION Nonmetals easily gain electrons to

attain a stable outer electron configuration.

An anion is a negatively charged ion that results from gaining one or more electrons.

GROUPS AND THEIR CHARGES A.K.A OXIDATION NUMBERS Since metals lose electrons during ionic

bonding and nonmetals gain electrons, we can assign charges to certain groups of the periodic table.

Group 1 = +1Group 2 = +2Group 13 = +3Group 14 = skipGroup 15 = -3Group 16 = -2Group 17 = -1Group 18 = no charge/stable configuration

IONIC BONDS An ionic bond forms when a metal atom

donates electrons to a nonmetal atom. The atom that donates electrons

becomes positively charged, and the atom that received the electrons becomes negatively charged.

The electrostatic force that holds oppositely charged particles together in an ionic compound is referred to as an ionic bond. (opposites attract)

RULES FOR WRITING IONIC BOND CHEMICAL FORMULAS In the chemical formula for any ionic

compound the symbol of the cation is always written first followed by the symbol of the anion.

Subscripts, which are numbers to the lower right of a symbol, represent the number of ions of each element in an ionic compound.

If no subscript is written it is assumed to be one.

The sum of the oxidation numbers must equal zero because ionic compounds are neutral.

DETERMINE THE FORMULA FOR THE FOLLOWING*NOTE: elements always combine in the

lowest whole number ratioK+ and Cl-

Na+ and O2-

Mg 2+ and S2-

Al3+ and O2-

POLYATOMIC IONS Ions made up of more than one atom. Refer to

the common ion handout and the back of your periodic table for the polyatomic ion formulas.

Many ionic compounds contain polyatomic ions.

A polyatomic ion acts as an individual ion in a compound and its charge applies to the entire group of atoms. ***NEVER CHANGE THE SUBSCRIPTS OF A POLYATOMIC ION!!

If more than one polyatomic ion is needed, place parentheses around the ion and write the appropriate subscript outside the parentheses.

DETERMINE THE FORMULA FOR THE FOLLOWINGNa+ and NO3

-

Ca 2+ and SO42-

Fe3+ and ClO3-

Cu2+ and C2H3O2-

Ba2+ and PO43-

NAMING IONIC COMPOUNDS1. Name the cation followed by the anion.

Remember that the cation is always written first in the formula.

2. For monatomic (one atom) cations, use the element name.

3. For monatomic anions, use the root of the element name plus the suffix –ide. Example: Na+ and Cl-

4. When the compound contains a polyatomic ion, simply name the cation followed by the name of the polyatomic ion.

Example: Na+ and C2H3O2-

NAMING IONIC COMPOUNDS WHEN THE CATION CAN HAVE MORE THAN ONE CHARGE

5. To distinguish between multiple oxidation numbers of the same element, the name of the chemical formula must indicate the oxidation number of the cation. The oxidation number is written as a Roman numeral in parentheses after the name of the cation.

Examples: Fe2+ and O2-

Fe3+ and O2-

PRACTICE PROBLEMS Name the following compounds:

NaBr

CaCl2

KOH

Cu(NO3)2

Ag2CrO4

PROPERTIES OF IONIC COMPOUNDS In an ionic compound, large numbers of

positive and negative ions exist together in a ratio determined by the number of electrons transferred from the metal atom to the nonmetal atom.

The ions pack into a regular repeating pattern to balance the attraction and repulsion between the ions. This forms a crystalline structure called a crystal lattice.

PROPERTIES: IONIC COMPOUNDS IN THE LIQUID STATE ARE ELECTROLYTES

In the solid state, the ions in an ionic compound are locked into fixed positions by strong attractive forces. As a result, ionic solids do not conduct electricity.

However, when ions are allowed to move freely in a molten liquid state or when dissolved in water, ionic compounds will conduct electricity. This is called an electrolyte.

PROPERTIES: IONIC CRYSTALS HAVE HIGH MELTING POINTS Because ionic bonds are relatively

strong, ionic crystals require a large amount of energy to be broken apart.

As a result, ionic crystals have high melting and boiling points.

PROPERTIES: IONIC CRYSTALS ARE HARD, RIGID, BRITTLE SOLIDS This is due to the strong attractive

forces that hold the ions in place.

LATTICE ENERGY The energy required to separate 1 mol of

the ions of an ionic compound is referred to as the lattice energy.

It is related to the size of the ions bonded and the charge of the ion.

Smaller ions produce greater attractions and higher lattice energies.

Example: the lattice energy of a lithium compound is greater than that of a potassium compound containing the same anion because the lithium ion is smaller than the potassium ion.

LATTICE ENERGY CONTINUED

The charge of the ion affects the value of the lattice energy.

The greater the charge of the positive and negative ions, the greater the lattice energy.Compoun

dLattice energy in kJ/mol

Compound

Lattice energy in kJ/mol

KI 632 KF 808

KBr 671 AgCl 910

RbF 774 NaF 910

NaI 682 LiF 1030

NaBr 732 SeCl2 2142

NaCl 769 MgO 3795

METALLIC BONDS AND THE PROPERTIES OF METALS

Although metals are not ionic, they share several properties with ionic compounds.

Metals often form lattices The electron sea model proposes that all

the metal atoms in a metallic solid contribute their valence electrons to form a “sea” of electrons. This sea of electrons surrounds the metal cations in the lattice.

PROPERTIES OF METALS A metallic bond is the attraction of a

metallic cation for delocalized electrons. This gives metals their properties such

as high melting points, malleability, ductility, durability, thermal and electrical conductivity, strength and hardness.