Chapter 1: Chemistry 101
Define heat energy in terms of the motion of particles.
Heat energy is a type of kinetic energy. Heat energy involves the kinetic energy of the particles within a substance. When a substance is heated, the particles within the substance vibrate or move more and more quickly. For example, if a stove is hot, the particles on the hot surface vibrate more rapidly than if the stove is cold. On the macroscopic level, the stove doesn't have kinetic energy (it is sitting still). But on the atomic level, the particles on the surface of the stove are moving rapidly. At higher temperatures, particles have more kinetic energy.
Describe the difference between composition and structure.
Composition refers to the simple components that make up the material. Structure refers to both the composition and arrangement of those simpler substances. For example, in Figure 1.4 we see a deck, a canoe, and a baseball bat. Each of these has basically the same composition: They are all made of wood. However, the wood is arranged in different structures that help each item fulfill its own function. In chemistry, we ask similar questions on a smaller scale: "What is the composition of wood?" That is, what is it made of? Or, "What is the structure of wood?" That is, how are its components arranged? Answering these questions helps us understand why substances behave the way they do.
Describe the relationship between the potential energy of a system and its potential for change.
In chemistry, we often describe substances as either high-energy or stable. When something has high energy (either kinetic or potential), it can bring about a change. On the other hand, if something is stable, it has less energy and is therefore less likely to react. Substances with a large amount of potential energy are more likely to react. For example, in Zimbabwe there is an extraordinary rock formation (Figure 1.18). Time and erosion have carved away much of the soil beneath the rocks, leaving them precariously balanced. Because these rocks sit high off the ground, they have a good deal of potential energy. Eventually, these rocks will fall. When they do, they will release this stored energy. Right now, you probably wouldn't want to camp underneath the rocks. But once the rocks fall, you have nothing more to worry about — the energy has been released, and the rock formation will be stable. The potential energy in any substance depends on its structure
Describe the three phases of matter.
Matter typically exists in one of three forms, which we call the three states of matter, or sometimes the three phases of matter. The three basic states of matter are solid, liquid, and gas. We distinguish between these states by properties that are visible on a macroscopic level (visible to the naked eye): Solids have both a definite shape and a definite volume. Liquids have a definite volume, but no definite shape. Liquids adopt the shape of their container. Next, let's begin to heat the solid aluminum. When we do this, the atoms vibrate faster. The more heat we add, the faster the atoms move. Eventually, they begin to break out of the rigid framework and travel freely past each other. The substance is now in the liquid state. The particles in a liquid move randomly, but they remain close to each other. Gases do not have a definite shape or a definite volume. Gases fill any container they occupy. If we continue heating the liquid aluminum, the atoms move faster and faster until they begin to break out of the liquid phase and enter the gas phase. Particles in the gas phase move about freely and have very little interaction with each other.
Compare and contrast physical and chemical properties and physical and chemical changes.
Physical properties are the properties of a substance that we can measure without changing the identity of the substance. For example, we can measure color, temperature, mass, volume, shape, hardness, flexibility, and a host of other factors without changing the composition of that substance. Similarly, physical changes are changes that occur without altering the identity of the substance. For example, we can take an iron bar, melt it, pour it into a mold, and let it cool, solidifying into a new shape. We have altered the shape and the phase of the iron, but it is still composed of iron, and so each of these changes is a physical change. In a physical change, the properties change but the composition stays the same. Chemical properties are properties that we cannot measure without changing the identity of a substance. For example, flammability is a chemical property. If we want to determine if something is flammable, we must try to burn it. If it burns, it is no longer the original substance. When a substance changes into something different, it has undergone a chemical change. Chemical changes are also called chemical reactions. In some chemical changes, elements combine to form compounds. For example, when heated, zinc and sulfur combine to form a new compound, zinc sulfide (Figure 1.14). In other chemical changes, compounds break apart to produce elemental substances or rearrange to form new compounds. The key idea is that a chemical change always involves the formation of a different substance.
Describe the key components of the scientific method.
The approach that scientists take to solving problems is called the scientific method. At its core, the scientific method is a cyclical process of making observations, formulating new ideas, and then testing those ideas through experiments. A cyclical process of making observations, formulating new ideas, and then testing those ideas through experiments.
Differentiate between elements, compounds, homogeneous mixtures, and heterogeneous mixtures.
The simplest form of matter is an element. An element is a substance that is made of only one type of atom. Common elements include gold, silver, iron, oxygen, and nitrogen. Each element is composed of a unique type of atom. For example, gold contains only gold atoms, and silver contains only silver atoms. Compounds are substances composed of more than one element, bound together in fixed ratios. For example, water is made of two parts hydrogen and one part oxygen. If the ratio of hydrogen to oxygen changes at all from 2:1, it is no longer water, but some other substance. Many compounds form groups of atoms called molecules. In contrast to pure substances, mixtures contain more than one substance — and the substances are not bound in a fixed ratio. For example, brass and bronze are both mixtures of metals, known as alloys. Brass is a mixture of the pure substances copper and zinc, while bronze is a mixture of the pure substances copper and tin (Figure 1.9). Mixtures whose components are evenly blended throughout are called homogeneous mixtures. Metal alloys, a cup of coffee, and the air around us are all homogeneous mixtures. A key difference between compounds and mixtures is that mixtures can be separated into their individual components without changing the identity of the substances. In contrast, heterogeneous mixtures contain regions with significantly different composition (Figure 1.10). Sand and water, gravel, and chocolate-chip cookie dough are all heterogeneous mixtures. They each have regions where one component is present in far greater proportion. Figure 1.11 summarizes the categories of pure substances and mixtures.
Describe the impact of chemistry on a variety of other fields.
Understanding what substances are made of and how they behave are the essence of the field of chemistry. Regardless of your background, your interests, or your career, your day-to-day activities involve chemistry. Are you interested in working in a health-care field? Chemistry is essential to understanding how our bodies function and how they interact with their surroundings. Are you interested in physics, engineering, or construction? What about computers and technology? The properties of trade materials — from concrete and steel to semiconductors and solar cells — depend on the composition and properties of the substances they are made of. Are you interested in agriculture or the environment? Everything from exploring rock formations to monitoring air, soil, and water quality involves chemistry. Chemistry is sometimes referred to as "the central science," because it connects with every other field in the sciences (Figure 1.2). Whether your passion lies in art, music, business, or sports, you can find ways that chemistry overlaps with these disciplines.
Explain the differences between a hypothesis, a theory, and a scientific law.
When scientists encounter a new or unexpected occurrence, they propose explanations for what they have observed. Scientists use the term hypothesis to describe a tentative explanation that has not been tested. To test a hypothesis, scientists devise experiments. The results of experiments provide support for or against a hypothesis, and they lead scientists to embrace, refine, or discard their ideas. The observations that scientists make from experiments often lead to new hypotheses, which in turn lead to new experiments. Through this cyclic process, scientists refine their ideas over time. A theory is an idea that is supported by experimental evidence. This term can also have a broader meaning: Sometimes it is used to mean a paradigm — a way of thinking about or analyzing a particular topic. Scientists use the term scientific law to describe observations that are true in widely varying circumstances. A scientific law does not explain why something occurs; it simply observes that it is true. Often, a scientific law describes a mathematical relationship. For example, consider the law of gravity: This law describes observations and phenomenon that consistently occur. Scientists use the law of gravity mathematically, to calculate the weight of a building or the trajectory of a rocket. This law predicts what will happen, but it does not explain why it happens. Scientific laws describe what happens, but not why. Theories describe how or why something happens
