Chemistry (9-1) - 0971 CIE

Formulae

Overview

A chemical formula is chemistry's shorthand: a few letters and numbers that capture exactly which atoms, and how many, make up a substance. From \(H_2O\) for water to \(C_6H_{12}O_6\) for glucose, formulae let chemists say precisely what something is and write equations that account for every atom in a reaction.

In this lesson you will learn to read and deduce formulae, tell a molecular formula from an empirical one, work out the formula of an ionic compound from the charges on its ions, and build balanced symbol equations with state symbols, including ionic equations. These are the skills every later topic relies on.

Objectives

State the formulae of the elements and compounds named in the subject content.
Define the molecular formula of a compound as the number and type of different atoms in one molecule.
Deduce the formula of a simple compound from the relative numbers of atoms present in a model or a diagrammatic representation.
Construct word equations and symbol equations to show how reactants form products, including state symbols.
[Supplement] Define the empirical formula of a compound as the simplest whole number ratio of the different atoms or ions in a compound.
[Supplement] Deduce the formula of an ionic compound from the relative numbers of the ions present in a model or a diagrammatic representation or from the charges on the ions.
[Supplement] Construct symbol equations with state symbols, including ionic equations.
[Supplement] Deduce the symbol equation with state symbols for a chemical reaction, given relevant information.

Lesson Note

Formulae and equations are the language of chemistry. You cannot calculate reacting masses, balance a reaction or predict a product without them. Getting formulae right, and balancing equations correctly, underpins almost every calculation and explanation in the rest of the course.

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Lesson Evaluation

Congratulations on completing the lesson on Formulae. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.

You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.

Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.

What does the molecular formula of a compound show? A. only the ratio of atoms B. the number and type of atoms in one molecule C. the mass of the compound D. the state of the compound Answer: B
The empirical formula of C6H12O6 is: A. C6H12O6 B. CH2O C. CHO D. C2H4O2 Answer: B
What is the formula of the compound formed from Mg2+ and Cl- ions? A. MgCl B. Mg2Cl C. MgCl2 D. Mg2Cl3 Answer: C
Which state symbol means aqueous? A. (s) B. (l) C. (g) D. (aq) Answer: D
In an ionic equation, ions that are unchanged on both sides are called: A. reacting ions B. spectator ions C. complex ions D. product ions Answer: B