Ionic Compounds and 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.

• 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 Na+ and Cl-, which combine to form NaCl.

Valence Electrons and the Octet Rule

Atoms tend to achieve a stable electron configuration, often resembling that of noble gases, by having eight valence electrons (the octet rule).

• 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)

Exceptions to the octet rule include hydrogen (stable with 2 electrons) and some transition metals.

Ions: Formation and Types

Ions are atoms or groups of atoms that have gained or lost electrons, resulting in a net charge.

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

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

Example: Magnesium (Mg) loses two electrons to form Mg2+; fluorine (F) gains one electron to form F-.

Common Ion Names

Anion	Name
F-	Fluoride
Cl-	Chloride
Br-	Bromide
I-	Iodide
O2-	Oxide
S2-	Sulfide
P3-	Phosphide
N3-	Nitride

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 include phosphate (PO43-), sulfate (SO42-), nitrate (NO3-), and acetate (C2H3O2-).

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

Ion	Name
ClO3-	Chlorate
ClO4-	Perchlorate
NO3-	Nitrate
SO42-	Sulfate
CO32-	Carbonate
PO43-	Phosphate
C2H3O2-	Acetate

Electron Dot Structures

Electron dot structures (Lewis structures) represent valence electrons as dots around the chemical symbol of an element.

• Helps visualize electron transfer in ionic bonding.

• Example: Na (1 dot) transfers its electron to Cl (7 dots), forming Na+ and Cl-.

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.

• Formula unit: The simplest ratio of ions that results in a neutral compound.

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

• For compounds: $\text{total } (+) = \text{total } (-)$

Properties of Ionic Compounds

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

• 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.

Metallic Bonds and 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.

• Good conductors of heat and electricity.

• Malleable (can be hammered into shapes) and ductile (can be drawn into wires).

Alloys

Alloys are mixtures of two or more elements, at least one of which is a metal, designed to enhance properties.

• Examples: Bronze (copper and tin), Sterling silver (silver and copper), Stainless steel (iron, carbon, chromium).

Naming and Writing Formula Units

Writing formulas for ionic compounds requires balancing the total positive and negative charges.

• Use subscripts to indicate the number of each ion needed to balance charge.

• Parentheses are used around polyatomic ions if more than one is needed.

• Example: $\text{Ca}^{2+} + 2\text{Cl}^- \rightarrow \text{CaCl}_2$

Sample Table: Common Ions and Formula Units

Ion	Formula Unit
K+, Cl-	KCl
Mg2+, SO42-	MgSO4
Ca2+, PO43-	Ca3(PO4)2
Fe3+, Cl-	FeCl3
Na+, NO3-	NaNO3

Summary Equations

• General charge balance: $\text{total } (+) + \text{total } (-) = 0$

Additional info: These notes also include practical examples and naming conventions for ionic compounds, as well as a brief overview of metallic bonding and alloys, which are essential for understanding the properties and applications of metals in chemistry.