Chemistry » Essential Ideas in Chemistry » Phases and Classification of Matter

Summarizing Phases and Classification of Matter

Summary of lessons so far

Chemistry in Context

Chemistry deals with the composition, structure, and properties of matter, and the ways by which various forms of matter may be interconverted. Thus, it occupies a central place in the study and practice of science and technology.

Chemists use the scientific method to perform experiments, pose hypotheses, and formulate laws and develop theories, so that they can better understand the behavior of the natural world. To do so, they operate in the macroscopic, microscopic, and symbolic domains. Chemists measure, analyze, purify, and synthesize a wide variety of substances that are important to our lives.

Phases and Classification of Matter

Matter is anything that occupies space and has mass. The basic building block of matter is the atom, the smallest unit of an element that can enter into combinations with atoms of the same or other elements. In many substances, atoms are combined into molecules.

On earth, matter commonly exists in three states: solids, of fixed shape and volume; liquids, of variable shape but fixed volume; and gases, of variable shape and volume. Under high-temperature conditions, matter also can exist as a plasma.

Most matter is a mixture: It is composed of two or more types of matter that can be present in varying amounts and can be separated by physical means. Heterogeneous mixtures vary in composition from point to point; homogeneous mixtures have the same composition from point to point.

Pure substances consist of only one type of matter. A pure substance can be an element, which consists of only one type of atom and cannot be broken down by a chemical change, or a compound, which consists of two or more types of atoms.

Glossary of Words


smallest particle of an element that can enter into a chemical combination


study of the composition, properties, and interactions of matter


pure substance that can be decomposed into two or more elements


substance that is composed of a single type of atom; a substance that cannot be decomposed by a chemical change


state in which matter has neither definite volume nor shape

Heterogeneous mixture

combination of substances with a composition that varies from point to point

Homogeneous mixture

(also, solution) combination of substances with a composition that is uniform throughout


tentative explanation of observations that acts as a guide for gathering and checking information


state of matter that has a definite volume but indefinite shape


statement that summarizes a vast number of experimental observations, and describes or predicts some aspect of the natural world

Law of conservation of matter

when matter converts from one type to another or changes form, there is no detectable change in the total amount of matter present

Macroscopic domain

realm of everyday things that are large enough to sense directly by human sight and touch


fundamental property indicating amount of matter


anything that occupies space and has mass

Microscopic domain

realm of things that are much too small to be sensed directly


matter that can be separated into its components by physical means


bonded collection of two or more atoms of the same or different elements


gaseous state of matter containing a large number of electrically charged atoms and/or molecules

Pure substance

homogeneous substance that has a constant composition

Scientific method

path of discovery that leads from question and observation to law or hypothesis to theory, combined with experimental verification of the hypothesis and any necessary modification of the theory


state of matter that is rigid, has a definite shape, and has a fairly constant volume

Symbolic domain

specialized language used to represent components of the macroscopic and microscopic domains, such as chemical symbols, chemical formulas, chemical equations, graphs, drawings, and calculations


well-substantiated, comprehensive, testable explanation of a particular aspect of nature


force that gravity exerts on an object

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