2: Essential Background

Most courses in Chemistry, especially those at the college/university level, assume that their students have had prior courses in general science, and often in physics, which provide them with an understanding of important concepts such as significant figures, units of measure, treatment measurement error, density and buoyancy. But  if most of that has receded into the fuzzy past, the six sections of this unit will bring you up to speed. Neglect this stuff at your peril —  it will come up in one way or another in any Chemistry course you take!

• 2.1: Classification and Properties of Matter
Matter is “anything that has mass and occupies space”. Matter is what chemical substances are composed of. But what do we mean by chemical substances? How do we organize our view of matter and its properties? These very practical questions will be the subjects of this lesson.
• 2.3: Energy, Heat, and Temperature
All chemical changes are accompanied by the absorption or release of heat. The intimate connection between matter and energy has been a source of wonder and speculation from the most primitive times; it is no accident that fire was considered one of the four basic elements (along with earth, air, and water) as early as the fifth century BCE. This unit will cover only the very basic aspects of the subject.
• 2.4: The Measure of Matter
The natural sciences begin with observation and this usually involves numerical measurements of quantities. Most of these quantities have units of some kind associated with them, and these units must be retained when you use them in calculations. All measuring units can be defined in terms of a very small number of fundamental ones that, through "dimensional analysis", provide insight into their derivation and meaning, and must be understood when converting between different unit systems.
• 2.5: The Meaning of Measure
In science, there are numbers and there are "numbers".  What we ordinarily think of as a "number" and will refer to here as a pure number is just that: an expression of a precise value.  The other kind of numeric quantity that we encounter in the natural sciences is a measured value of something– the length or weight of an object, the volume of a fluid, or perhaps the reading on an instrument. Although we express these values numerically, it would be a mistake to regard them as pure numbers.