Chapter 4: Chemical Bonding – General Chemistry Study Notes

Chapter 4: Chemical Bonding

Lecture Outline

• 4.1 Chemical Bonds and Greenhouse Gases

• 4.2 Electronegativity and Bonding

• 4.3 Naming Compounds and Writing Formulas

• 4.4 Lewis Symbols and Lewis Structures

• 4.5 The Lengths and Strengths of Covalent Bonds

• 4.6 Resonance

• 4.7 Formal Charge: Choosing among Lewis Structures

• 4.8 Exceptions to the Octet Rule

4.1 Chemical Bonds and Greenhouse Gases

Mixtures and Compounds

Chemical bonds are fundamental to the formation of compounds, which are substances composed of two or more elements chemically combined in fixed ratios. When elements combine, the resulting compound has properties distinct from its constituent elements.

• Mixture: A physical combination of substances where the ratio of components can vary. Example: A balloon filled with hydrogen and oxygen gases.

• Compound: A chemical combination of elements in a fixed ratio. Example: Water (H2O), where each molecule contains two hydrogen atoms and one oxygen atom.

Table: Selected Properties of Hydrogen and Oxygen

Property	Hydrogen	Oxygen
Boiling Point	−253 °C	−183 °C
State at Room Temperature	Gas	Gas
Flammability	Explosive	Necessary for combustion

Chemical Bonds

A chemical bond forms due to the attraction between charged particles (electrons and nuclei) in atoms. There are two main types of chemical bonds:

• Ionic Bonds: Formed between metals and nonmetals by the transfer of electrons, resulting in cations and anions.

• Covalent Bonds: Formed between two or more nonmetals by sharing electrons between atoms.

Lewis (Electron Dot) Symbols

Definition and Application

Electron-dot symbol (Lewis symbol): An atomic symbol surrounded by dots representing the number of valence electrons. These symbols help visualize how atoms bond and achieve stable electron configurations.

• Each dot represents a valence electron.

• Up to 8 valence electrons can be shown (octet rule), with two electrons on each side of the element symbol.

• Electrons are placed one per side before pairing (Hund's rule analogy).

Example: Lewis Dot Structure for Oxygen

• Oxygen has 6 valence electrons: O with six dots around it.

Octet Rule

The octet rule states that atoms tend to gain, lose, or share electrons to achieve a noble gas configuration of 8 valence electrons (except for hydrogen, which achieves 2).

• Lewis symbols are used to predict bonding patterns and the formation of molecules.

Bonding Types and Lewis Symbols

• Lewis symbols are most commonly used for covalent bonding (nonmetal + nonmetal), but can also represent ionic bonding (metal + nonmetal).

Summary Table: Ionic vs. Covalent Bonds

Bond Type	Participants	Electron Movement	Resulting Species
Ionic	Metals + Nonmetals	Transfer electrons	Cation + Anion
Covalent	2 or more Nonmetals	Share electrons	Atom + Atom

Key Points

• Valence electrons are the electrons involved in bonding and are represented in Lewis symbols.

• Lewis structures help predict how atoms bond and the arrangement of electrons in molecules.

• The octet rule guides the formation of stable compounds.

Example: Water Formation

• Hydrogen and oxygen combine to form water (H2O), a compound with properties different from its elements.

• Water molecules have a fixed ratio of hydrogen to oxygen (2:1), unlike mixtures where ratios can vary.

Additional info: Later sections (not shown in images) cover electronegativity, naming compounds, Lewis structures, resonance, formal charge, and exceptions to the octet rule, which are all foundational topics in General Chemistry.