Ionic Compounds & Metals: Structure, Properties, and Nomenclature

Chapter 7: Ionic Compounds & Metals

Introduction to Chemical Bonding

Chemical bonding involves the interaction of electrons between atoms, resulting in the formation of compounds. The two primary types of chemical bonds are ionic bonds and covalent bonds, each with distinct properties and formation mechanisms.

• Ionic Bonds: Formed by the transfer of electrons from metals to nonmetals, resulting in the creation of oppositely charged ions that attract each other.

• Covalent Bonds: Formed by the sharing of electrons between nonmetal atoms.

• Valence Electrons: Electrons in the outermost shell, crucial for bonding and chemical reactivity.

Example: Sodium (Na) transfers one electron to chlorine (Cl) to form NaCl, an ionic compound.

Valence Electrons and the Octet Rule

Valence electrons determine an atom's chemical properties and its ability to bond. The octet rule states that atoms tend to gain, lose, or share electrons to achieve a stable configuration of eight valence electrons.

• Group 1A: 1 valence electron

• Group 2A: 2 valence electrons

• Group 3A: 3 valence electrons

• Group 4A: 4 valence electrons

• Group 5A: 5 valence electrons

• Group 6A: 6 valence electrons

• Group 7A: 7 valence electrons

• Group 8A: 8 valence electrons (noble gases, most stable)

Exceptions: Hydrogen and Helium are stable with 2 electrons (duet rule).

Ions: Cations and Anions

Ions are atoms or groups of atoms with a net electric charge due to the loss or gain of electrons.

• Cations: Positively charged ions formed when metals lose electrons (e.g., Na+, Ca2+).

• Anions: Negatively charged ions formed when nonmetals gain electrons (e.g., Cl-, O2-).

Common Cations: Na+ (sodium), Ca2+ (calcium), Mg2+ (magnesium)

Common Anions: F- (fluoride), Cl- (chloride), O2- (oxide), S2- (sulfide), N3- (nitride), P3- (phosphide)

Polyatomic Ions

Polyatomic ions are covalently bonded groups of atoms that carry a net charge and act as a single unit in chemical reactions.

• Examples: NO3- (nitrate), SO42- (sulfate), PO43- (phosphate), NH4+ (ammonium), ClO3- (chlorate), CO32- (carbonate), C2H3O2- (acetate)

• Names ending in -ate or -ite indicate oxygen-containing polyatomic ions.

Electron Dot Structures

Electron dot structures (Lewis structures) represent valence electrons as dots around the chemical symbol, helping visualize bonding and lone pairs.

• Example: Na: one dot; Cl: seven dots

• Shows how electrons are transferred or shared in bond formation.

Formation of Ionic Compounds

Ionic compounds are formed when metals transfer electrons to nonmetals, resulting in the formation of cations and anions that attract each other to form a neutral compound.

• General formula: Total positive charge = total negative charge

• Subscripts indicate the number of each ion needed to balance the charges.

Example: $\text{Na}^+ + \text{Cl}^- \rightarrow \text{NaCl}$

Sample Problem: Mg2+ and Cl- combine to form MgCl2.

Properties of Ionic Compounds

Ionic compounds exhibit distinct physical and chemical properties due to their structure and bonding.

• Bound by strong electrostatic attractions between ions.

• Neutral overall charge.

• Form crystalline (3D) lattice structures.

• Conduct electricity when molten or dissolved in water.

• Commonly referred to as salts.

• Represented by formula units showing the lowest whole-number ratio of ions.

Example: NaCl, K2O

Metallic Bonds and Properties of Metals

Metallic bonds are the attraction between free-floating valence electrons and positively charged metal ions, resulting in unique properties for metals.

• Metals are composed of cations surrounded by a 'sea' of delocalized electrons.

• Properties:

  • Good conductors of heat and electricity

  • Malleable (can be hammered into shapes)

  • Ductile (can be drawn into wires)

Alloys: Mixtures of two or more elements, at least one of which is a metal (e.g., bronze, sterling silver, stainless steel).

Naming and Writing Formula Units for Ionic Compounds

Naming and writing formulas for ionic compounds requires balancing the total positive and negative charges and using subscripts to indicate the number of each ion.

• Use parentheses around polyatomic ions if more than one is needed.

• Practice problems involve combining cations and anions to write correct formula units.

Ion Name	Ion Symbol	Formula Unit Example
Sodium chloride	Na+, Cl-	NaCl
Calcium phosphate	Ca2+, PO43-	Ca3(PO4)2
Magnesium sulfate	Mg2+, SO42-	MgSO4
Iron(III) chloride	Fe3+, Cl-	FeCl3
Aluminum oxide	Al3+, O2-	Al2O3

Example: To write the formula for calcium chloride, combine Ca2+ and Cl- to get CaCl2.

Summary Equation for Ionic Compounds

The sum of the positive and negative charges in an ionic compound must equal zero:

$\text{total } (+) + \text{total } (-) = 0$

Additional info: These notes cover the essential concepts of ionic and metallic bonding, ion formation, properties of ionic compounds, and the rules for naming and writing formulas for ionic compounds, as outlined in a typical General Chemistry curriculum.