BackChemical Formulas and Formula Mass: Study Notes
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Chemical Formulas and Formula Mass
Introduction to Chemical Formulas
Chemical formulas are symbolic representations of the elements present in a compound and the ratios in which they combine. Understanding chemical formulas is fundamental to studying chemical reactions, stoichiometry, and molecular structure.
Empirical Formula: Shows the simplest whole-number ratio of atoms in a compound.
Molecular Formula: Indicates the actual number of each type of atom in a molecule.
Structural Formula: Depicts the arrangement of atoms within the molecule (often shown as ball-and-stick models).
Example: The molecular formula for caffeine is C8H10N4O2.
Atomic Mass and Molar Mass
Atomic mass is the mass of a single atom, typically expressed in atomic mass units (amu), while molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). The molar mass is numerically equal to the atomic or molecular mass in amu, but with units of g/mol.
Key Atomic Masses:
Carbon (C): 12.01 g/mol
Hydrogen (H): 1.008 g/mol
Nitrogen (N): 14.01 g/mol
Oxygen (O): 16.00 g/mol
Sodium (Na): 22.99 g/mol
Formula Mass: The sum of the atomic masses of all atoms in a chemical formula. For molecules, this is called molecular mass; for ionic compounds, it is called formula mass.
Example Calculation: For caffeine (C8H10N4O2):
Using Molar Mass as a Conversion Factor
Molar mass allows conversion between the mass of a substance and the number of moles. This is essential for quantitative chemical calculations.
Conversion Formula:
Example: What is the mass of 3.50 mol N2?
Periodic Table and Atomic Masses
The periodic table provides atomic masses for all elements, which are used to calculate formula and molar masses. Elements are organized by increasing atomic number and grouped by similar chemical properties.
Main Groups: Alkali metals, alkaline earth metals, halogens, noble gases, etc.
Transition Metals: Elements in the center block of the table.
Lanthanides and Actinides: Elements in the two rows below the main table.
Practice Problems and Applications
Applying the concepts of chemical formulas and molar mass is crucial for solving quantitative problems in chemistry.
Example 1: How many moles of H are in 0.20 mol C7H14N2? Each molecule contains 14 H atoms, so:
Example 2: How many moles of H are in 16 g of NaOH? Molar mass of NaOH = 22.99 + 15.999 + 1.008 = 39.997 g/mol Each NaOH contains 1 H atom, so:
Comparison Table: Atomic Masses of Common Elements
The following table summarizes the atomic masses of several elements commonly used in formula mass calculations.
Element | Symbol | Atomic Mass (g/mol) |
|---|---|---|
Carbon | C | 12.01 |
Hydrogen | H | 1.008 |
Nitrogen | N | 14.01 |
Oxygen | O | 16.00 |
Sodium | Na | 22.99 |
Visual Representations
Ball-and-stick models and crystal lattice diagrams help visualize molecular and ionic structures, respectively. These models illustrate the spatial arrangement of atoms and ions in compounds.
Molecular Model: Shows atoms as spheres and bonds as sticks (e.g., caffeine molecule).
Ionic Lattice Model: Represents the repeating pattern of ions in a solid (e.g., NaCl crystal).
Additional info: Some images and text were inferred to represent standard chemical models and periodic table organization. Calculations and examples were expanded for clarity and completeness.
