Overview
This lecture introduces the concept of the mole as a key conversion factor in chemistry, enabling conversion between atoms, moles, and grams using the periodic table.
The Mole and Its Importance
- The mole connects the mass of a substance (in grams) to the number of atoms it contains.
- 1 mole = 6.022 × 10²³ particles (Avogadro's number), which simplifies calculations involving atoms.
- The atomic mass unit (amu) is useful for single atoms, but grams are used for practical laboratory measurements.
Conversion Factors Using the Mole
- 6.022 × 10²³ protons or neutrons ≈ 1 gram.
- 6.022 × 10²³ carbon-12 atoms = 12 grams of carbon (from the periodic table).
- 1 mole of any element = its atomic mass in grams (from the periodic table).
Using the Periodic Table
- Atomic mass on the periodic table (amu) can be read as grams per mole for an element.
- Example: 1 atom of Mg = 24.31 amu; 1 mole of Mg = 24.31 g and contains 6.022 × 10²³ atoms.
Calculations and Examples
- To find the number of atoms in 2 moles of carbon: 2 × 6.022 × 10²³ = 1.20 × 10²⁴ atoms.
- To find the mass of 2 moles of carbon: 2 × 12.011 g = 24.022 g.
- To convert 36 g of carbon to moles: 36 g ÷ 12.011 g/mole = 3.0 moles.
- To convert 36 g of carbon to atoms: 36 g × (1 mole/12.011 g) × (6.022 × 10²³ atoms/1 mole) = 1.8 × 10²⁴ atoms.
Molar Mass
- Molar mass is the mass of one mole of a substance, found on the periodic table.
- Example: Sodium (Na) has a molar mass of 22.99 g/mole; Lithium (Li) is 6.94 g/mole.
Stepwise Problem Solving with Moles
- Start with grams, convert to moles using molar mass, then convert moles to atoms using Avogadro’s number.
- To find moles in 14.2 g of lithium: 14.2 g ÷ 6.94 g/mole = 2.046 moles.
- To find atoms in 14.2 g of lithium: 14.2 g × (1 mole/6.94 g) × (6.022 × 10²³ atoms/1 mole).
Key Terms & Definitions
- Mole — A unit representing 6.022 × 10²³ particles of a substance.
- Avogadro's Number — 6.022 × 10²³, the number of particles in a mole.
- Molar Mass — The mass in grams of one mole of a substance, as found on the periodic table.
- Atomic Mass Unit (amu) — A unit for expressing the mass of a single atom or molecule.
Action Items / Next Steps
- Practice mole conversions using different elements from the periodic table.
- Complete assigned problems involving grams, moles, and atoms calculations.