7

Molecules and Chemical Formulas

• Definition of a Molecule

  • A molecule is defined as a fixed number of atoms that are held together by chemical bonds in a specific spatial arrangement.

• Chemical Formulas

  • A chemical formula symbolically represents the type and number of each element present in a molecule.

Viewpoints in Chemistry

• Chemists utilize three distinct viewpoints to study and understand matter:

  1. Macroscopic Viewpoint

  • This perspective involves observing matter on a large scale, which can typically be measured or seen with the naked eye.

  1. Symbolic Viewpoint

  • This viewpoint uses chemical symbols and formulas to represent the substances and their relationships mathematically.

  1. Particulate Viewpoint

  • This view considers matter at the atomic and molecular level, emphasizing the interactions and arrangements of individual particles.

Visualizing Molecules in Air

• Molecules in the air can be visualized by understanding their chemical composition based on the above-mentioned definitions and viewpoints.

Prefixes for Molecular Compounds

• Prefixes are utilized to denote the number of each type of element in molecular compounds. Below is a list of common prefixes:

Naming Molecular Compounds

Naming Hydrocarbons

• The general formula for hydrocarbons is represented as: $C<em>xH</em>{2x+2}$

  • Examples of hydrocarbon formulas and their corresponding names include:

  • Methane

  • Chemical Formula: $CH_4$

  • Number of Carbon Atoms: 1

  • Ethane

  • Chemical Formula: $C<em>2H</em>6$

  • Number of Carbon Atoms: 2

  • Propane

  • Chemical Formula: $C<em>3H</em>8$

  • Number of Carbon Atoms: 3

  • Butane

  • Chemical Formula: $C<em>4H</em>{10}$

  • Number of Carbon Atoms: 4

  • Pentane

  • Chemical Formula: $C<em>5H</em>{12}$

  • Number of Carbon Atoms: 5

  • Hexane

  • Chemical Formula: $C<em>6H</em>{14}$

  • Number of Carbon Atoms: 6

  • Heptane

  • Chemical Formula: $C<em>7H</em>{16}$

  • Number of Carbon Atoms: 7

  • Octane

  • Chemical Formula: $C<em>8H</em>{18}$

  • Number of Carbon Atoms: 8

  • Nonane

  • Chemical Formula: $C<em>9H</em>{20}$

  • Number of Carbon Atoms: 9

  • Decane

  • Chemical Formula: $C<em>{10}H</em>{22}$

  • Number of Carbon Atoms: 10

Rules for Naming Molecular Compounds

1. Element Naming

   • Name each element in the chemical formula, modifying the name of the second element to end in –ide.

     • For example:

     • Sulfur becomes sulfide.

     • Oxygen becomes oxide.

2. Using Prefixes in Chemical Formulas

   • Utilize prefixes to indicate the numbers of atoms in the chemical formula.

     • Example: $N<em>2O</em>5$ is named dinitrogen pentoxide.

3. Omitting Prefixes

   • If there is only one atom for the first element in the chemical formula, omit the prefix mono-.

     • Example: $CO$ is named carbon monoxide, not monocarbon monoxide.