BackChapter 4: Basic Chemical Bonding – Elements, Compounds, and Molecular Structure
Study Guide - Smart Notes
Tailored notes based on your materials, expanded with key definitions, examples, and context.
Elements and Molecules
Definitions and Classifications
Chemical substances can be classified as elements or compounds, with further distinctions based on their molecular structure and bonding type.
Element: A pure substance consisting of only one type of atom. Elements may exist as single atoms or as molecules composed of two or more identical atoms joined by covalent bonds (e.g., O2, H2).
Molecule: A discrete, uncharged group of two or more atoms held together by covalent bonds. Molecules can be elements (e.g., O2) or compounds (e.g., H2O).
Compound: A substance composed of two or more different elements combined in fixed, definite proportions. Compounds can be broken down into simpler substances by chemical means.
Molecular (Covalent) Compound: Formed by the reaction between two or more nonmetals, involving the sharing of electrons (covalent bond). Example: H2O, CO2, glucose (C6H12O6).
Ionic Compound: Formed by the transfer of one or more electrons from a metal to a nonmetal, resulting in electrostatic attraction between oppositely charged ions. Example: sodium chloride (NaCl).
Example Table: Classification of Pure Substances
Type | Example | Description |
|---|---|---|
Element (Molecular) | O2 | Two oxygen atoms joined by a covalent bond |
Compound (Molecular) | H2O | Two hydrogen atoms and one oxygen atom joined by covalent bonds |
Compound (Ionic) | NaCl | Sodium and chloride ions held together by electrostatic attraction |
Classification of Elements and Compounds
Periodic Table and Types of Elements
The periodic table classifies elements as metals, nonmetals, and metalloids. This classification helps predict the types of compounds they form:
Metals: Tend to lose electrons and form cations; commonly participate in ionic bonding.
Nonmetals: Tend to gain electrons and form anions; commonly participate in covalent bonding.
Metalloids: Exhibit properties intermediate between metals and nonmetals.
Key Point: Ionic compounds typically form between metals and nonmetals, while covalent compounds usually involve only nonmetals.
Chemical Formulas
Types of Chemical Formulas
Chemical formulas represent the composition of substances and can be expressed in several ways:
Empirical Formula: Shows the simplest whole-number ratio of elements in a compound. Example: CH for benzene.
Molecular Formula: Shows the actual number of each type of atom in a molecule. Example: C6H6 for benzene.
Structural Formula: Shows how atoms are connected within a molecule. Example: CH3CH2OH for ethanol.
Models: Ball-and-stick and space-filling models visually represent molecular shapes and relative atom sizes.
Ionic vs. Covalent Compounds
Physical Properties Comparison
Ionic and covalent compounds differ in their physical properties due to the nature of their bonding.
Property | Ionic Compounds | Covalent Compounds |
|---|---|---|
Physical State | Solid (crystalline) | Solid, liquid, or gas |
Melting Point | High (above 300°C) | Low (below 300°C) |
Electrical Conductivity | Poor in solid state; good when melted or dissolved | Poor |
Example: Table salt (NaCl) is an ionic compound, while water (H2O) is a covalent compound.
Summary Table: Metals, Nonmetals, and Metalloids
Type | Location on Periodic Table | Typical Bonding |
|---|---|---|
Metals | Left and center | Ionic (with nonmetals) |
Nonmetals | Upper right | Covalent (with other nonmetals) |
Metalloids | Staircase between metals and nonmetals | Variable |
Key Concepts and Applications
Pure substances can be elements or compounds.
Molecular compounds are formed by covalent bonding between nonmetals.
Ionic compounds are formed by electron transfer between metals and nonmetals.
Chemical formulas provide information about the types and ratios of atoms in a substance.
Physical properties such as melting point and conductivity help distinguish ionic and covalent compounds.
Example Application: Classify the following as element, molecular compound, or ionic compound: O2 (element), H2O (molecular compound), NaCl (ionic compound).
Additional info: These notes are based on textbook-style content and lecture slides, with some inferred context to clarify definitions and examples.
