Chapter 8 Ionic Compounds

I. Chemical Bonds The force that holds two atoms together Valence electrons are involved in the formation of chemical bonds between two atoms Electron dot diagrams are used to keep track of valence electrons and are useful when illustrating the formation of chemical bonds

A. Formation of Positive Ions Results when an atom loses one or more valence electrons in order to attain a noble gas configuration A positively charged ion is called a cation Some transition elements lose electrons to form an outer energy level containing full s, p, and d sublevels - These relatively stable electron arrangements are referred to as pseudo- noble gas configurations

B. Formation of Negative Ions Results when an atom gains one or more valence electrons in order to attain a noble gas configuration A negatively charged ion is called an anion - To designate an anion, -ide is added to the root name of the element (chloride) Example: Na + Cl - is sodium chloride

II. Formation of an Ionic Bond An ionic bond is the electrostatic force that holds oppositely charged particles together in an ionic compound Most ionic compounds are called salts Ionic bonds between metals and the nonmetal oxygen, are called oxides

Many ionic compounds are binary, which means that they contain only two different elements - Contain a metallic cation and a nonmetallic anion

III. Properties of Ionic Compounds Positive and negative ions are packed together in a repeating pattern that balances the charge of the ions involved - Forms an ionic crystal in a ratio determined by the number of electrons transferred from the metal to the nonmetal

A crystal lattice is a three-dimensional geometric arrangement of particles - Each positive ion is surrounded by negative ions - Each negative ion is surrounded by positive ions

Ionic crystals vary in shape due to the sizes of ions bonded Ionic crystals are also hard, rigid, and brittle solids Ionic bonds are relatively strong and require a large amount of energy to be broken apart - Results in high melting points and boiling points

A. Energy and the Ionic Bond In any chemical reaction, energy is either absorbed or released - When energy is absorbed during a chemical reaction, the reaction is endothermic - When energy is released, it is an exothermic reaction

The formation of ionic compounds is always exothermic - Positive ions and negative ions are attracted to one another, forming a more stable compound that is lower in energy than the two individual ions

The energy required to separate the ions of an ionic compound is equal to the energy released in their formation - Referred to as the latice energy - The more negative the latice energy, the stronger the force of attraction

Lattice energy is directly related to the size of the ions bonded - Smaller ions generally have amore negative value for lattice energy because the nucleus is closer to and thus has more attraction for the valence electrons 0

Lattice energy is also related to the charge of the ion - Ions with larger positive or negative charges generally have a more negative lattice energy Example Mg +2 O -2 has a more negative lattice energy than Na + F -

IV. Formulas for Ionic Compounds A formula unit represents the simplest ratio of ions involved in an ionic compound The overall charge of a formula unit is zero Example MgCl2 contains Mg 2 +Cl 2 - The symbol of the cation is always written first, followed by the symbol of the anion Subscripts are used to represent the number of ions of each element in an ionic compound

A. Determining Charge The numbers of electrons transferred to or from an atom of the element to form an ion is its oxidation number Oxidation numbers of ions are used to determine the formulas for the ionic compounds they form The ratio of ions must be such that the number of electrons lost by the metal is equal to the number of electrons gained by the nonmetal

B. Compounds that contain polyatomic ions Monatomic ions are made of only one atom Polyatomic ions are made of more than one atom (NH 4 +, NO 2 -, NO 3 - ) but act as an individual ion The charge given to a polyatomic ion applies to the entire group of atoms

C. Nomenclature of Ionic Compounds Polyatomic ions composed of a nonmetal and one or more oxygens are called oxyanions

1. The following rules apply for nonmetals with only two oxanyions a. The ion with more oxygen atoms (usually 3 or more) is named using the root of the nonmetal plus the suffix -ide b. The ion with less oxygen atoms (usually 2 or less) is named using the root of the nonmetal plus the suffix -ite

2. If more than two oxyanions for a nonmetal exist, the following rules apply a. The oxyanion with the greatest number of oxygen atoms is named using the prefix per-, the root of the nonmetal, and the suffix -ate b. The oxyanion with one less oxygen atom than the most, is named with the root of the nonmetal and the suffix -ate

c. The oxyanion with the least number of oxygen atoms is named using the prefix hypo-, the root of the nonmetal, and the suffix –ite d. The oxyanion with one more oxygen atom than the least, is named with the root of the nonmetal and the suffix –ite

3. Naming Ionic Compounds a. Name the cation first and the anion second b. Monatomic cations use the element name (sodium chloride in NaCl) c. Monatomic anions take their name from the root of the element name plus the suffix –ide (sodium chloride in NaCl)

d. Elements with more than one oxidation number (transition metals and metals on the right side of the periodic table) must be distinguished from one another - The oxidation number is written as a Roman numeral in parenthesis after the name of the cation

V. Metallic Bonds In metallic bonds, electrons are ‘pooled’ together Metals form lattices with one metal atom being surrounded by 8 to 12 other metal atoms Outer energy levels of the metal atoms overlap

All the metal atoms in a metallic solid contribute their valence electrons to from a “sea” of electrons Valence electrons are not held by any specific atom and can move easily from one atom to the next - Often referred to as delocalized electrons A metallic cation is formed and is bonded to all neighboring metal cations

A. Properties of Metals Generally have moderately high melting points and high boiling points Malleable, easily hammered into sheets Ductile, easily drawn into wire Durable Delocalized electrons interact with light, absorbing and releasing photons, thereby creating the property of luster in metals

The movement of mobile electrons around cations explains why metals are good conductors - Move heat from one place to another quickly - When an electrical potential is applied to a metal, mobile electrons easily move as a part of an electric current

VI. Metal Alloys A mixture of elements that have metallic properties Most commonly form when the elements involved are either similar in size (substitutional alloys) or the atoms of one element are considerably smaller than the atoms of the other (interstitial alloys)