answers to the end of chapter questions
Digital images of the in-text figures
0 Fundamentals
At the end of this chapter, students should be able to:
Recognise the base SI quantities used in chemistry and state their symbols and units
Convert between commonly used SI units
Write numbers using scientific notation
Recognise metric prefixes used in expressing large or small numbers.
Understand the use of significant figures when expressing quantities and measurements and be able to round values to the correct number of significant figures
Write chemical formulae and equations and balance equations
Use the appropriate symbol to indicate the physical state of a substance in a chemical equation
0.1 Introduction to chemistry
Chemistry is a subject that underpins many other disciplines. At the heart of chemistry is the study of the elements that make up the periodic table, the reactions they undergo, and the new compounds that are formed.
Water is a compound that we are all familiar with, and most people know the formula for water is H2O even if they know nothing else about chemistry. The formula of water tells us that it is a molecule made up of two atoms of the element hydrogen and one atom of the element oxygen. In your course, you will learn that the elements in the periodic table are composed of atoms and that atoms are made up of smaller particles called protons, neutrons, and electrons. It is the specific combination of protons, neutrons, and electrons that gives each element its particular properties.
Hydrogen and oxygen are two of the smallest and lightest elements in the periodic table. Both hydrogen and oxygen are gases at room temperature, whereas water is a liquid. During your studies, you will learn why certain substances are gases or liquids, with low melting points and boiling points, and why other substances are solids that are very difficult to break down or melt. These properties depend to a certain extent upon how the atoms are arranged in molecules of the substances. For example, a water molecule has a bent shape (Figure 0.1). The bent shape of the water molecule is one of the factors that determines the melting and boiling point of water and ensures that it is a liquid at ambient temperatures. If the atoms in water were arranged in a straight line, water would have a much lower boiling point and would likely be a gas at room temperature. Clearly, this would have a major impact on life on earth. In this course, you will learn how to predict the shapes of small molecules such as water and see how important shape is in chemistry.
Figure 0.1 The shape of a water molecule, H2O.
In this chapter, we will introduce some of the fundamental tools necessary for studying, understanding, and applying chemical principles. You may have met some of these rules before in other subject areas, and you will probably meet them again later in the book, but this chapter should act as a toolbox from which you can select the information and guidance you need for the rest of the course.
0.2 Measurement in chemistry and science – SI units
Chemistry is a practical subject, and our present knowledge of chemical properties and principles is based on experiments. Unfortunately, we don't have space in this book to describe many of the amazing experiments that early investigators carried out to enhance our understanding and knowledge of chemistry. The majority of experiments require making and recording measurements. The laws of science operate across the globe, so it's important that scientists make measurements that can be compared with each other. Therefore, measurements must be recorded in a universal and standard way. For this reason, the metric system was developed to establish a standardised set of units. The metric system has its origins in the eighteenth century. More recently, a revised metric system was introduced and adopted by scientists across the world. This system is known as the Système Internationale d'Unités, and the units in the system are known as SI units.
There are seven fundamental SI units. Six of these are commonly used in chemistry, and you will meet all of them in this course. The six base units used in chemistry are listed in Table 0.1 and are the units of mass, length, time, electrical current, temperature, and amount of substance. All other units for physical quantities can be reduced to these base units. For example, speed is defined as the distance or length travelled divided by the time taken, so:
Table 0.1 Base SI quantities used in chemistry with symbols and units.
| Physical quantity | Symbol | Base unit | Unit symbol |
|---|---|---|---|
| Mass | m | kilogram | kg |
| Length | l | metre | m |
| Time | t | second | s |
| Electrical current | I | ampere | A |
| Temperature | T | kelvin | K |
| Amount of substance | n | mole | mol |
This defines the unit of speed as metre per second or m/s. In chemistry, as in most other scientific subjects, this would be written as: m s−1, where the superscript ‘−1’ means ‘per second’.
There are many other units you will come across that can be reduced down to these base units. Units of this type are called derived units and usually have their own symbol. A list of derived units and their symbols is given in Table 0.2.
Dealing with exponents
Exponents tell us how many times a number should be multiplied by itself. For example:
