1: Matter and Measurements

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1.1: Basic Definitions
Chemistry is the study of matter and its interactions with other matter and energy. Matter is anything that has mass and takes up space. Matter can be described in terms of physical properties and chemical properties. Physical properties and chemical properties of matter can change. Matter is composed of elements and compounds. Combinations of different substances are called mixtures. Elements can be described as metals, nonmetals, and semimetals.
1.4: Chemistry as a Science
Science is a process of knowing about the natural universe through observation and experiment. Scientists go through a rigorous process to determine new knowledge about the universe; this process is generally referred to as the scientific method. Science is broken down into various fields, of which chemistry is one. Science, including chemistry, is both qualitative and quantitative.
1.5: Expressing Numbers
Standard notation expresses a number normally. Scientific notation expresses a number as a coefficient times a power of 10. The power of 10 is positive for numbers greater than 1 and negative for numbers between 0 and 1.
1.6: Significant Figures - Writing Numbers to Reflect Precision
Uncertainty exists in all measurements. The degree of uncertainty is affected in part by the quality of the measuring tool. Significant figures give an indication of the certainty of a measurement. Rules allow decisions to be made about how many digits to use in any given situation.
1.7: The Basic Units of Measurement
Metric prefixes derive from Latin or Greek terms. The prefixes are used to make the units manageable. The SI system is based on multiples of ten. There are seven basic units in the SI system. Five of these units are commonly used in chemistry.
1.8: Problem Solving and Unit Conversions
During your studies of chemistry (and physics also), you will note that mathematical equations are used in a number of different applications. Many of these equations have a number of different variables with which you will need to work. You should also note that these equations will often require you to use measurements with their units. Algebra skills become very important here!
1.9: Temperature and Density
Chemistry uses the Celsius and Kelvin scales to express temperatures. A temperature on the Kelvin scale is the Celsius temperature plus 273.15. The minimum possible temperature is absolute zero and is assigned 0 K on the Kelvin scale. Density relates a substance's mass and volume. Density can be used to calculate volume from a given mass or mass from a given volume.
1.10: Hypothesis, Theories, and Laws
Although all of us have taken science classes throughout the course of our study, many people have incorrect or misleading ideas about some of the most important and basic principles in science. We have all heard of hypotheses, theories, and laws, but what do they really mean? Before you read this section, think about what you have learned about these terms before. What do these terms mean to you? What do you read contradicts what you thought? What do you read supports what you thought?
1.11: Classification of Matter
Matter can be classified according to physical and chemical properties. Matter is anything that occupies space and has mass. The three states of matter are solid, liquid, and gas. A physical change involves the conversion of a substance from one state of matter to another, without changing its chemical composition. Most matter consists of mixtures of pure substances, which can be homogeneous (uniform in composition) or heterogeneous (different regions possess different compositions & properties.
1.12: Activity: States of Matter
Explore the interactions between various combinations of two atoms. Observe the the total force acting on the atoms or the individual attractive and repulsive forces. Customize the attraction to see how changing the atomic diameter and interaction strength affects the interaction.
1.13: Compounds Display Constant Composition
A compound is a substance that contains two or more elements chemically combined in a fixed proportion. The elements carbon and hydrogen combine to form many different compounds. One of the simplest is called methane, in which there are always four times as many hydrogen particles as carbon particles. Methane is a pure substance because it always has the same composition. However, it is not an element because it can be broken down into simpler substances - carbon and hydrogen.
1.14: Chemical Formulas: How to Represent Compounds
A chemical formula is an expression that shows the elements in a compound and the relative proportions of those elements. A molecular formula is a chemical formula of a molecular compound that shows the kinds and numbers of atoms present in a molecule of the compound. An empirical formula is a formula that shows the elements in a compound in their lowest whole-number ratio.
1.15: A Molecular View of Elements and Compounds
Most elements exist with individual atoms as their basic unit. It is assumed that there is only one atom in a formula if there is no numerical subscript on the right side of an element’s symbol. There are many substances that exist as two or more atoms connected together so strongly that they behave as a single particle. These multi-atom combinations are called molecules. The smallest part of a substance that has the physical and chemical properties of that substance.
1.16: Methods for Separating Mixtures
In a chemical reaction, it is important to isolate the component(s) of interest from all the other materials so they can be further characterized. Studies of biochemical systems, environmental analysis, pharmaceutical research - these and many other areas of research require reliable separation methods. Here are a number of common separation techniques:
1.17: Properties of Matter
All matter has physical and chemical properties. Physical properties are characteristics that scientists can measure without changing the composition of the sample under study, such as mass, color, and volume (the amount of space occupied by a sample). Chemical properties describe the characteristic ability of a substance to react to form new substances; they include its flammability and susceptibility to corrosion.
1.18: What is Energy?
Energy is the ability of a system to do work. A system has done work if it has exerted a force on another system over some distance. When this happens, energy is transferred from one system to another
1.19: Energy and Chemical and Physical Change
Phase changes involve changes in energy. All chemical reactions involve changes in energy. This may be a change in heat, electricity, light, or other forms of energy. Reactions that absorb energy are endothermic. Reactions that release energy are exothermic.
1.20: Activity: Energy Forms and Changes
Explore how energy is transferred to different systems to perform work.