Chapter 5: Ionic and Covalent Compounds – Structured Study Notes

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, naming conventions, and calculations involving chemical formulas. These concepts are essential for understanding the structure and properties of compounds 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.

• Valence electrons: Electrons that participate in chemical bonding.

• Group number: Indicates the number of valence electrons for main group elements.

Group	Electron Configuration	# of Valence Electrons
1A	ns1	1
2A	ns2	2
3A	ns2np1	3
4A	ns2np2	4
5A	ns2np3	5
6A	ns2np4	6
7A	ns2np5	7

Lewis Dot Symbols

Lewis dot symbols represent valence electrons as dots around the chemical symbol of an element. They are used for main group elements to visualize bonding capacity.

• One dot for each valence electron.

• Only main group elements use Lewis dot symbols.

• Number of valence electrons equals the group number (exception: He has 2 valence electrons).

Example: Carbon (C) has 4 dots; Oxygen (O) has 6 dots.

Ionic Compounds and Bonding

Ionic Bonding

An ionic bond is formed by the complete transfer of valence electrons from a metal to a nonmetal, resulting in the formation of cations and anions held together by electrostatic forces.

• Ionic bond: Complete transfer of electrons from metal to nonmetal.

• Octet rule: Atoms tend to gain or lose electrons to achieve a noble gas electron configuration (8 valence electrons).

• Electrostatic force: Attraction between oppositely charged ions.

Example: Formation of NaCl (sodium chloride):

• Sodium (Na) loses one electron to become Na+.

• Chlorine (Cl) gains one electron to become Cl-.

• Resulting compound is neutral: NaCl.

Equations:

• Ionization: $\mathrm{Li} \rightarrow \mathrm{Li}^+ + e^-$

• Electron acceptance: $\mathrm{F} + e^- \rightarrow \mathrm{F}^-$

Ionic Compounds

Ionic compounds are neutral substances composed of cations and anions. The total positive and negative charges must balance.

• Cation: Positively charged ion (e.g., Na+, Mg2+).

• Anion: Negatively charged ion (e.g., Cl-).

• Example: MgCl2 (magnesium chloride) – Mg2+ and two Cl- ions.

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" and no prefixes are used.

• NaCl: Sodium chloride

• Na2S: Sodium sulfide

• MgO: Magnesium oxide

• Al2O3: Aluminum oxide

Important: No prefixes are used in naming Type 1 ionic compounds.

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.

• Subscript of cation = charge of anion

• Subscript of anion = charge of cation

Example: Calcium chloride (CaCl2): Ca2+ and two Cl- ions.

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 spread over two or more atoms.

Ion	Formula	Ion	Formula
Acetate	CH3COO-	Mercury (II)	Hg2+
Ammonium	NH4+	Nitrate	NO3-
Bicarbonate	HCO3-	Nitrite	NO2-
Carbonate	CO32-	Perchlorate	ClO4-
Chlorate	ClO3-	Permanganate	MnO4-
Cyanide	CN-	Phosphate	PO43-
Hydronium	H3O+	Sulfate	SO42-
Hydroxide	OH-	Sulfite	SO32-
Mercury (I)	Hg22+

Writing Ionic Compounds with Polyatomic Ions

When writing formulas for ionic compounds containing polyatomic ions, the net charge must still be zero. Use parentheses if more than one polyatomic ion is needed.

• Example: Sodium carbonate: Na2CO3

• Example: Ammonium sulfate: (NH4)2SO4

Additional info:

• Further sections in the original notes cover Type 2 ionic compounds (transition metals), covalent bonding, molecular formulas, naming molecular compounds, acids and bases, and calculations involving molar mass and percent composition. These topics are essential for a complete understanding of chemical compounds in general chemistry.