Chemistry is one of the three major areas in science, along with biology and physics. In this chapter, we will first propose a definition for chemistry and discuss its scope. Then, we will turn our attention to the principal concern of chemistry: matter.
It is important to understand the definition of chemistry in its historical context.
Chemistry—Definition, Practitioners, and History
Chemistry is the science of matter and the changes it undergoes. The main focus of chemistry is matter. All objects in the world are types of matter.
A chemist is a person who studies the composition, structure, and properties of matter and seeks to explain the changes that matter undergoes.
Modern chemistry grew out of the pseudoscience called alchemy. Alchemists searched for methods to convert base metals to gold. Robert Boyle (1627–1691) was one of the first scientists to suggest that ideas and thoughts about matter must be supported by reproducible experiments. Antoine Lavoisier (1743–1794) is credited with being the father of modern chemistry because of his pioneering experiments on the properties of matter.
Matter, Mass, and Energy
Matter is anything that has mass and occupies space. The mass of an object is a measure of the amount of matter it has. Closely related to matter is energy. Thus, chemistry also considers the relationship of matter and energy.
Energy is the capacity to do work, or more simply, the capacity to change something.
1.2 MATTER AND ITS PROPERTIES This section focuses on the definition of chemistry, which involves matter and the changes matter undergoes.
Composition and Structure
Composition refers to the identity and amount of the components of matter. Structure describes the physical arrangement of its particles (atoms, ions, or molecules). Some types of matter have a highly organized structure, while others are random.
Physical Properties and Changes
Chemists distinguish one type of matter from another by identifying their properties, just as people are differentiated by observing their physical appearance and personality traits. Properties are classified as being either physical or chemical. Physical properties are characteristics of a particular type of matter that can be measured without changing its composition. Density, color, melting point, boiling point, physical state, heat conductivity, and electrical conductivity are examples of physical properties of matter.
If a change occurs in the physical properties of a sample of matter without a change in composition, a physical change occurs. After such a change, the same type of matter is present but has a different set of physical properties. Changes in shape, size, and physical state are other examples of physical changes.
Chemical Properties and Changes
A chemical property describes what happens to one type of matter when it changes composition. When the matter changes its composition, a chemical reaction or chemical change occurs. Therefore, chemical properties describe the chemical reactions that matter undergoes. For example, a chemical property of gasoline is that it burns (undergoes oxidation) when ignited. Gasoline is a liquid mixture of carbon-hydrogen compounds.
Exercise 1.1
Classify each of the following as a physical property, physical change, chemical property, or chemical change: (a) A blue solid, (b) an explosive liquid, and (c) a solid changes directly to a vapor without becoming a liquid.
Solution 1.1
(a) A physical property, because it is a characteristic of a solid without reference to any other substance. (b) A chemical property, because explosive describes a chemical change that the liquid undergoes. (c) A physical change, because the solid does not change composition.
1.3 CLASSIFICATION OF MATTER Samples of matter can be classified as being either pure substances or mixtures.
Pure Substances
Pure substances (or, simply, substances) have a constant composition, cannot be separated into simpler components by physical methods, and undergo state changes at a constant temperature. Examples of pure substances include gold, copper, and carbon dioxide. Pure substances can be further subdivided into elements or compounds.
Mixtures
A mixture results when pure substances that do not react are combined. Mixtures have a variable composition, can usually be separated by physical methods, and undergo state change over range of temperatures. Mixtures can either be homogenous (those with one phase) or heterogeneous (those with two or more phases). Ocean water, concrete, air, and asphalt are four examples of mixtures.
Elements
Elements are the basic units of matter. All of the types of matter contain elements. About 115 different elements have been identified. Of these elements, 92 occur in nature, and the remaining elements are synthetic. At 25°C, 102 elements are solids, 2 are liquids, and 11 are gases.
Periodic Table of Elements
The symbols of the elements are found in the Periodic Table. This tab...
