Understanding Matter: Properties, Changes, and Laws

Physical Property

A characteristic of matter that can be observed or measured without changing the sample’s composition; also describes a pure substance having a uniform and unchanging composition.

Extensive Property

Physical properties that are dependent on the amount of a substance present, such as length, shape, weight, and volume.

Intensive Properties

Physical properties of matter that are independent of the amount of a substance, such as density, color, and specific heat.

Chemical Properties

The ability or inability of a substance to combine with or change into one or more other substances, such as iron forming rust or copper forming a greenish patina.

Physical Change

A change that alters the substance without changing its composition.

Phase Change

The physical transition of a substance from one form of matter to another based on temperature and/or pressure, such as an ice cube melting to form water.

Chemical Change

A process that causes one or more substances to change into one or more new substances, also called a chemical reaction, where the new substances have different composition and different properties from the initial substances.

Conservation of Mass

The Law of Conservation of Mass states that matter can neither be created nor destroyed but only changed in form, as through a chemical reaction, and therefore matter is conserved.

Conservation of Energy

The Law of Conservation of Energy states that energy can neither be created nor destroyed but only changed in form or converted from one form to another.

Mixture

The combination of two or more pure substances in which each substance retains its individual chemical properties. Can be separated through a physical process.

Heterogeneous Mixtures

A mixture that does not blend smoothly and in which individual substances remain distinct.

Homogeneous Mixtures

A mixture that has a constant composition throughout and always has a single phase.

Solutions

Homogeneous mixtures that can be any combination of solids, liquids, or gases.

Separation Techniques

• Filtration: A technique that uses a porous barrier to separate solids from liquids in a solution.
• Distillation: A physical technique to separate different liquids in a solution based on differences in boiling point.
• Crystallization: A separation technique that results in the formation of a pure solid particle of a substance from a solution containing the dissolved substance.
• Sublimation: The process through which a solid changes into vapor without melting, going through a liquid phase.
• Chromatography: A technique that separates the components of a mixture dissolved into a gas or liquid based on the ability of each component to travel or be drawn across the surface of a fixed substrate.

Element

A pure substance that cannot be broken down into simpler substances by physical or chemical means without losing its unique nature. Each element has a unique chemical name and symbol.

Periodic Table

An organized graphic representation of all known elements into horizontal rows called periods and columns called groups or families. Elements in the same group have similar chemical and physical properties.

Compound

A pure substance made up of two or more different elements that are combined chemically.

Laws of Chemical Combination

• Law of Definite Proportions: A compound is always composed of the same elements in the same proportion by mass, no matter how large or small the sample.
• Law of Multiple Proportions: When different compounds are formed by a combination of the same elements, the masses of one element combine with the same fixed mass of the other element in a ratio of small whole numbers.