What is the difference between empirical and molecular formulas?

An empirical formula represents the simplest whole-number ratio of atoms in a compound (e.g. CH2 for ethylene). A molecular formula shows the actual number of each atom in a molecule (e.g. C2H4).

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Core Study Guide

Chemical Compounds

Molecular weights, Avogadro's number, and the mole concept.

Stoichiometry is the quantitative calculation of reactants and products in chemical reactions based on the conservation of mass.

This unit defines the mole (a fundamental SI unit representing Avogadro's constant) and covers molar mass conversions and stoichiometric ratios.

Key Takeaways

•One mole of any substance contains exactly 6.022 × 10²³ elementary entities.
•Molar mass is the mass of one mole of a substance (expressed in g/mol).
•Balanced chemical equations provide molar ratios required to perform reaction stoichiometry.

Core Concepts & Definitions

1The Mole & Avogadro's Number

The mole acts as a bridging unit between atomic scale mass and macroscopic measurements.

•Avogadro's Constant: N_A = 6.022 × 10²³ particles/mol.

•Moles = Mass (g) / Molar Mass (g/mol).

Quick Revision Notes

•Always balance a chemical equation before attempting stoichiometry calculations.
•Stoichiometry converts mass of reactant → moles of reactant → moles of product → mass of product.