A material composed of two or more substances is a mixture. A pure substance is a form of matter that has a constant composition and properties that are constant throughout the sample. Matter can be classified into two broad categories: pure substances and mixtures. 1.10: Classifying Matter According to Its Composition One useful way of organizing our understanding of matter is to think of a hierarchy that extends down from the most general and complex to the simplest and most fundamental.We want a definite amount of voltage - no more and no less. If it is more, the equipment will be damaged. If the voltage is less, the system will not work. We want the same voltage (110 volts for the U.S.) to come from the outlet to whatever we plug in. What we also want (although we usually don't think about it) is for the electricity supply to be the same wherever we go. 1.8: Law of Definite Proportions Wherever we travel in the United States, we want electricity to be available.The modern atomic theory establishes the concepts of atoms and how they compose matter. 1.5: Atomic Theory Atoms are the ultimate building blocks of all matter.Unprotected by enamel, a tooth will start to decay, thus developing cavities and other dental problems. Acids found in some foods or made by bacteria that feed on food residues on our teeth are capable of dissolving enamel. It has to be hard so that our teeth can serve us for a lifetime of biting and chewing however, tough as it is, tooth enamel is susceptible to chemical attack. 1.4: Prelude to Elements, Atoms, and the Periodic Table The hardest material in the human body is tooth enamel.Matter is anything that has mass and takes up space-that is, anything that is physically real. Being able to describe the ingredients in a cake and how they change when the cake is baked is called chemistry. 1.2: What is Chemistry? Chemistry is the study of matter-what it consists of, what its properties are, and how it changes.In chemistry, as in any technical endeavor, the proper expression of quantities is a necessary fundamental skill. Both parts of a quantity, the amount (55) and the unit (mph), must be properly communicated to prevent potential problems. The posted speed limits on roads and highways, such as 55 miles per hour (mph), are quantities we might encounter all the time. 1.1: Prelude to Chemistry, Matter, and Measurement Quantities and measurements are as important in our everyday lives as they are in medicine.
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