Avogadro's Number
Avogadro's number (, approximately 6.022 x 10²³), is a fundamental constant in chemistry. It defines the number of particles (atoms, molecules, ions, etc.) in one mole of any substance. This immense number allows chemists to relate the macroscopic world (grams, liters) to the microscopic world (atoms, molecules).
- = 6.02214076 × 10²³ particles/mol
- Defines the mole, the SI unit for amount of substance
- Applies universally to atoms, molecules, ions, or any specified particles
- Serves as a universal conversion factor between moles and number of particles
Molecular Quantities
When dealing with chemical compounds, understanding molecular quantities is key. This involves distinguishing between atomic mass (mass of a single atom) and molecular mass (sum of atomic masses in a molecule). Chemical formulas provide the exact ratio of atoms in a molecule, which is crucial for calculating total atoms in a compound.
- Atomic vs. Molecular Mass: Atomic mass refers to individual atoms, while molecular mass is for compounds.
- Polyatomic Molecules: Molecules composed of multiple atoms (e.g., H₂O, CO₂).
- Isotopic Abundance: The relative amount of each isotope of an element, affecting average atomic mass.
- Chemical Formulas: Represent the types and numbers of atoms in a molecule (e.g., H₂O for water).
- Empirical Formulas: Show the simplest whole-number ratio of atoms in a compound.
Applications
Calculations involving atoms and moles are foundational to many scientific disciplines and practical applications:
- Stoichiometry: Predicting quantities of reactants and products in chemical reactions.
- Nuclear Chemistry: Understanding radioactive decay and nuclear reactions.
- Quantum Mechanics: Describing the behavior of matter at the atomic and subatomic levels.
- Material Science: Designing new materials with specific properties based on atomic structure.
- Analytical Chemistry: Determining the composition of substances.
Common Conversions
Here are some useful reference values and examples to illustrate the concept of moles and Avogadro's number:
- 1 mol H atoms = 6.022 × 10²³ hydrogen atoms
- 1 mol H₂O = 6.022 × 10²³ water molecules
- 1 mol H₂O (water) contains 1.807 × 10²⁴ total atoms (2 H atoms + 1 O atom per molecule)
- 1 mol NaCl (table salt) contains 1.204 × 10²⁴ total ions (6.022 × 10²³ Na⁺ ions + 6.022 × 10²³ Cl⁻ ions)