Chapter 5: Ionic and Covalent Compounds

Introduction

This chapter covers the fundamental principles of ionic and covalent compounds, including the nature of chemical bonding, Lewis dot symbols, the formation and naming of compounds, and calculations involving molecular and molar masses. These concepts are essential for understanding chemical structure and reactivity in general chemistry.

Lewis Dot Symbols

Valence Electrons and Bonding

Valence electrons are the electrons in the outermost shell of an atom and are primarily responsible for chemical bonding. The number of valence electrons for main group elements corresponds to their group number in the periodic table.

• 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

Lewis Dot Symbols

Lewis dot symbols visually represent the valence electrons of an atom as dots around the element's symbol. They are used for main group elements to illustrate bonding capacity.

• Each dot represents one valence electron.

• Number of dots equals the group number (except for He, which has 2 valence electrons).

• Helium is an exception: it is shown with two dots.

Example: Carbon (Group 4A) is represented as •C• with four dots.

Ionic Compounds and Bonding

Ionic Bonding

An ionic bond is formed by the complete transfer of valence electron(s) from a metal to a nonmetal, resulting in the formation of cations and anions held together by electrostatic forces. Ionic bonds follow the octet rule, aiming for noble gas electron configurations.

• Metal atoms lose electrons to form cations.

• Nonmetal atoms gain electrons to form anions.

• Octet rule: Atoms tend to gain, lose, or share electrons to achieve eight valence electrons.

Example: Formation of NaCl:

• Sodium () loses one electron:

• Chlorine () gains one electron:

• Resulting compound:

Ionic Compounds

Ionic compounds are electrically neutral substances composed of cations and anions.

• Sodium chloride (): Sodium cation () and chloride anion ()

• Magnesium chloride (): Magnesium cation () and two chloride anions ()

Example:

Chemical Ions and Ionic Compounds

Naming Type 1 Ionic Compounds

Type 1 ionic compounds consist of a metal (from Groups 1, 2, or 3) and a nonmetal. The nonmetal's name ends with "-ide." No prefixes are used.

• NaCl: Sodium chloride

• Na2S: Sodium sulfide

• MgO: Magnesium oxide

• Al2O3: Aluminum oxide

Writing Ionic Compounds (Type 1)

The net charge of an ionic compound must be zero. The subscripts in the formula are determined by balancing the charges of the cation and anion.

• Example: Sodium fluoride (): and combine in a 1:1 ratio.

• Example: Calcium chloride (): and combine in a 1:2 ratio.

Trick: The subscript of the cation equals the charge of the anion, and vice versa.

Polyatomic Ions

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

• Lose or gain electrons as a group.

• Charge is distributed over two or more atoms.

Writing Ionic Compounds with Polyatomic Ions

Apply Type 1 rules: the net charge must be zero. Use parentheses for polyatomic ions when more than one is needed.

• Example: Sodium carbonate (): and combine in a 2:1 ratio.

• Example: Ammonium sulfate (): and combine in a 2:1 ratio.

*Additional info: The above table and examples are inferred from standard general chemistry curriculum and the provided notes.*