Читать книгу Foundations of Chemistry - Philippa B. Cranwell - Страница 15

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.