General chemistryLesson 1 of 2 in the course Atoms, Molecules, and Ions

Chemical Formulas, Empirical Ratios, and Isomers

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Chemical formulas provide a compact way to describe the atoms in a substance. In this lesson, you will learn how to read molecular formulas, distinguish them from structural formulas and models, and interpret subscripts and coefficients correctly.

A molecular formula uses element symbols to show which kinds of atoms are in a molecule. Subscripts show how many atoms of each element are present. For example, methane has the molecular formula CH4CH_4: one carbon atom and four hydrogen atoms. A subscript is written only when more than one atom of that element is present; the missing subscript means one.

All flashcards

Molecular formula
Uses element symbols and subscripts to show the actual number of each atom in a molecule.
Empirical formula
Shows the simplest whole-number ratio of atoms or ions in a compound.
Structural formula
Shows atom types and counts, as well as how the atoms are connected.
Isomers
Compounds with the same chemical formula but different molecular structures.
Ball-and-stick and space-filling models
Ball-and-stick models emphasize geometric arrangement; space-filling models emphasize relative sizes and occupied space.

Quiz questions

  1. What is the empirical formula of glucose, whose molecular formula is C6H12O6C_6H_{12}O_6?Answer: CH2OCH_2O
  2. What makes two compounds structural isomers?Answer: They have the same formula but different atom-to-atom connections.
  3. What distinguishes spatial isomers?Answer: Their atoms have different three-dimensional arrangements.
  4. What does 2H22H_2 represent?Answer: Two hydrogen molecules containing four hydrogen atoms in total.
  5. What information does a molecular formula preserve that an empirical formula may not?Answer: The actual number of each type of atom in one molecule.

Based on Chemistry 2e by Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson, PhD (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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