Chap 6

Ions and Ionic Compounds

Formation of Ions

Atoms form ions by gaining or losing electrons to achieve a stable electron configuration, often resembling that of noble gases.

• Cations: Positively charged ions formed when atoms lose electrons (typically metals).

• Anions: Negatively charged ions formed when atoms gain electrons (typically nonmetals).

• Example: Sodium (Na) loses one electron to form Na+; chlorine (Cl) gains one electron to form Cl-.

Electron Gain and Loss in Common Elements

• Aluminum (Al): Loses 3 electrons to form Al3+.

• Chlorine (Cl): Gains 1 electron to form Cl-.

• Sodium (Na): Loses 1 electron to form Na+.

Symbolism for Ions

• Ion Notation: The symbol for an ion includes its charge as a superscript (e.g., K+, Ca2+).

• Example: An atom with 19 protons and 18 electrons is K+ (potassium ion).

Properties of Ions

• Anions always have a negative charge.

• Cations always have a positive charge.

Formulas and Naming of Ionic Compounds

Writing Formulas for Ionic Compounds

Ionic compounds are formed from cations and anions in ratios that produce a neutral overall charge.

• Example: Magnesium chloride is MgCl2 (Mg2+ and two Cl-).

• Oxide ion: O2-

• Compound with Na+ and PO43-: Na3PO4

Naming Ionic Compounds

• Binary Ionic Compounds: Name the cation first, then the anion (e.g., NaCl is sodium chloride).

• Transition Metals: Use Roman numerals to indicate charge (e.g., FeSO4 is iron(II) sulfate).

• Polyatomic Ions: Compounds containing polyatomic ions retain the ion's name (e.g., NaNO3 is sodium nitrate).

Common Polyatomic Ions

Ion	Name
SO42-	Sulfate
NO3-	Nitrate
OH-	Hydroxide
PO43-	Phosphate

Covalent (Molecular) Compounds

Formation and Naming

Covalent compounds are formed when two or more nonmetals share electrons.

• Prefixes are used to indicate the number of atoms (e.g., CO2 is carbon dioxide).

• Examples: N2O3 is dinitrogen trioxide; CCl4 is carbon tetrachloride.

Diatomic Molecules

• Diatomic Elements: H2, N2, O2, F2, Cl2, Br2, I2

• Example: Carbon does not exist as a diatomic molecule.

Bond Types and Polarity

Ionic vs. Covalent Bonds

• Ionic Bonds: Formed between metals and nonmetals; involve transfer of electrons.

• Covalent Bonds: Formed between nonmetals; involve sharing of electrons.

• Example: CaO contains an ionic bond; H2O contains polar covalent bonds.

Polarity of Molecules

• Electronegativity: Determines bond polarity; higher difference leads to more polar bonds.

• Polar Molecules: Have an uneven distribution of charge (e.g., NH3, H2O).

• Nonpolar Molecules: Have an even distribution of charge (e.g., CO2).

• Example: The bond between H and O is polar covalent; CO2 is linear and nonpolar.

Intermolecular Forces

Types of Intermolecular Forces

• Dispersion Forces: Present in all molecules, especially nonpolar ones (e.g., Cl2).

• Dipole-Dipole Attractions: Occur between polar molecules (e.g., HBr).

• Hydrogen Bonds: Strongest type, occur when H is bonded to N, O, or F (e.g., NH3).

Summary Table: Key Concepts

Concept	Example	Key Point
Ionic Compound	NaCl	Metal + Nonmetal
Covalent Compound	CO2	Nonmetal + Nonmetal
Polyatomic Ion	SO42-	Multiple atoms, charge
Polar Molecule	NH3	Uneven charge distribution
Nonpolar Molecule	CO2	Even charge distribution

Important Formulas and Equations

• General Ionic Compound Formula: $\text{Cation}^{n+} + \text{Anion}^{m-} \rightarrow \text{Compound}$

• Example for Magnesium Chloride: $\text{Mg}^{2+} + 2\text{Cl}^{-} \rightarrow \text{MgCl}_2$

• Example for Sodium Phosphate: $3\text{Na}^{+} + \text{PO}_4^{3-} \rightarrow \text{Na}_3\text{PO}_4$

Additional info:

• Some questions and answers were inferred to provide complete academic context and explanations.

• All key terms and examples are relevant to GOB Chemistry and suitable for college-level study.