Molecules, Compounds, and Nomenclature: Study Notes

Molecules, Compounds, and Nomenclature

Chapter Overview

This chapter introduces the fundamental concepts of molecules and compounds, the types of chemical bonds, how to represent compounds using chemical formulas and molecular models, and the rules for naming compounds. It also covers the mole concept as it applies to compounds and methods for determining chemical formulas from experimental data.

Chemical Bonds

Types of Chemical Bonds

Chemical bonds are the forces that hold atoms together in compounds. The two main types of chemical bonds are ionic bonds and covalent bonds.

• Ionic Bonds: Formed when electrons are transferred from one atom (typically a metal) to another (typically a nonmetal), resulting in the formation of oppositely charged ions that attract each other.

• Covalent Bonds: Formed when two nonmetal atoms share one or more pairs of electrons.

Example: Sodium chloride (NaCl) forms via ionic bonding between sodium (Na) and chlorine (Cl). Water (H2O) forms via covalent bonding between hydrogen and oxygen.

Representing Compounds: Chemical Formulas and Molecular Models

Chemical Formulas

Chemical formulas provide information about the composition of compounds. There are several types:

• Empirical Formula: Gives the relative number of atoms of each element in a compound (the simplest whole-number ratio).

• Molecular Formula: Gives the actual number of atoms of each element in a molecule of the compound.

• Structural Formula: Shows how atoms are connected to each other using lines to represent chemical bonds.

Example: For water (H2O):

• Empirical formula: H2O

• Molecular formula: H2O

• Structural formula: H–O–H

Molecular Models

Molecular models visually represent the three-dimensional structure of molecules. Common types include:

• Ball-and-Stick Model: Atoms are shown as spheres and bonds as sticks.

• Space-Filling Model: Atoms are shown as spheres that are scaled to the size of the atoms and overlap to show bonding.

Molecular Formula	Structural Formula	Ball-and-Stick Model	Space-Filling Model
CH4
C2H2
C2H6O
H2O

Additional info: Images are referenced for illustration; in a text-only format, describe the models as above.

Key Points

• Empirical formulas are useful for ionic compounds and for determining the simplest ratio of elements.

• Molecular formulas are important for molecular compounds, especially organic molecules.

• Structural formulas and models help visualize the actual arrangement of atoms in space.