Ionic and Molecular Compounds Study Notes

Ionic and Molecular Compounds: Chapter 6 Overview

Introduction to Pharmacy Technicians

  • Pharmacy technicians work in various health facilities such as hospitals, pharmacies, clinics, and long-term care facilities.

  • They are responsible for the preparation and distribution of pharmaceutical medications based on doctors' orders.

Learning Goals

  • Write symbols for simple ions of representative elements.

  • Understand how atoms lose, gain, or share electrons to achieve a stable octet in forming ionic or covalent bonds.

6.1 Ions: Transfer of Electrons

  • Ionic Bonds: Formed through the transfer of valence electrons from a metal atom to a nonmetal atom, resulting in a charged ion.

  • Covalent Bonds: Formed when nonmetal atoms share electrons to achieve a noble gas configuration.

Characteristics of Ionic and Covalent Bonds

  • Ionic Bonds:

    • Metals lose one or more of their valence electrons.

    • Nonmetals gain valence electrons to reach an octet.

  • Covalent Bonds:

    • Electrons are shared between nonmetals to achieve stability.

Positive Ions: Loss of Electrons

  • Metals (Groups 1A (1), 2A (2), and 3A (13)) have low ionization energies and readily lose electrons to become cations (positively charged ions).

  • Cation Naming: The name of the cation is the same as the metal name.

  • Example: Sodium (Na) loses one electron:

    • Neutral: 11 protons, 11 electrons

    • Ion: 10 electrons, 11 protons; ionic charge: 1+ (Na+).

  • Example: Magnesium (Mg) loses two electrons:

    • Neutral: 12 protons, 12 electrons

    • Ion: 10 electrons, 12 protons; ionic charge: 2+ (Mg2+).

Negative Ions: Gain of Electrons

  • Nonmetals (Groups 5A (15), 6A (16), and 7A (17)) gain electrons to form anions (negatively charged ions).

  • Anion Naming: Use the first syllable of the element name plus the "-ide" ending.

  • Example: Chlorine (Cl) gains one electron:

    • Ion: 18 electrons, 17 protons; charge: 1− (Cl−).

Formulas, Names of Common Ions

Metals Group Number

Cation Name


Nonmetals Group Number

Anion Name

1A (1)

Li+ (Lithium)


5A (15)

N³− (Nitride)


Na+ (Sodium)


P³− (Phosphide)

6A (16)


K+ (Potassium)


O²− (Oxide)

7A (17)

2A (2)

Mg²+ (Magnesium)


S²− (Sulfide)



Ca²+ (Calcium)


F− (Fluoride)



Ba²+ (Barium)


Cl− (Chloride)


3A (13)

Al³+ (Aluminum)


Br− (Bromide)

I− (Iodide)

Ionic Charges, Group Numbers

  • The group number in the periodic table can help predict charges for ions in representative elements.

Important Ions in the Body

  • Sodium (Na+): Regulates body fluids, found in salt and cheese.

  • Potassium (K+): Vital for cellular functions, found in bananas and potatoes.

  • Calcium (Ca²+): Major cation in bones, crucial for muscle contractions, found in milk and greens.

  • Magnesium (Mg²+): Involved in enzyme functions, found in nuts and grains.

Ionic Compounds

  • Consist of positive and negative ions with ionic bonds.

  • Characterized by high melting points and solid state at room temperature.

  • Sodium Chloride (NaCl): Example of an ionic compound, represents the crystalline structure of Na+ and Cl− ions.

Chemical Formulas of Ionic Compounds

  • Formulas represent the lowest whole number ratio of atoms in the compound.

  • The sum of ionic charges must equal zero; for example:

    • For MgCl2: Mg²+ and 2 Cl− (1(2+) + 2(1−) = 0).

Writing Ionic Formulas from Ionic Charges

  • When balancing charges, the total positive charge must equal total negative charge.

  • Example for Barium and Chlorine ions: Ba²+ and 2 Cl− gives formula BaCl2.

Naming Ionic Compounds

  • Metal's name is written first followed by the nonmetal’s name with an "-ide" ending.

  • Example: K2O is named potassium oxide.

Transition Metals

  • Transition metals can form multiple charges; a Roman numeral indicates the charge in the compound name.

  • Example: Fe2+ is iron(II), Fe3+ is iron(III).

Writing Formulas for Ionic Compounds with Variable Charges

  • Determine the charge from the anion and apply charge balance.

  • Example: For iron(III) chloride (FeCl3), iron is Fe3+, chloride is Cl−. The formula balances as 1(3+) + 3(1−) = 0.

Polyatomic Ions

  • Polyatomic ions consist of covalently bonded atoms carrying an ionic charge. Charge balance is critical when writing formulas.

  • Common Polyatomic Ions:

    • Sulfate (SO4²−), Phosphate (PO4³−), Nitrate (NO3−).

Naming Molecular Compounds

  • Molecular compounds form through covalent bonding where atoms share electrons.

  • Naming: Use prefixes to indicate the number of atoms. Example: CO2 is carbon dioxide, CO is carbon monoxide.

Lewis Structures

  • Represent valence electrons in molecules to show bonding and nonbonding pairs.

  • Example: H2 forms via sharing electron pairs in a covalent bond; Lewis structure shows the electron arrangement.

Electronegativity and Bond Polarities

  • Electronegativity determines how electrons are shared in bonds; higher values indicate a stronger pull on electrons.

  • Types of Bonds:

    • Nonpolar covalent (electronegativity difference 0.0 - 0.4)

    • Polar covalent (0.5 - 1.8)

    • Ionic (greater than 1.8).

Molecular Shapes

  • Geometry affects polarity; three-dimensional shapes are predicted using VSEPR theory.

  • Common Shapes: Linear, Trigonal Planar, Tetrahedral, Bent, and Trigonal Pyramidal.

Intermolecular Forces

  • Types include hydrogen bonds, dipole-dipole attractions, and dispersion forces.

  • Affect physical properties such as boiling points and melting points of substances.