Chapter 3

substance

A form of matter that has a uniform and unchanging composition; also known as a pure substance.

physical property

A characteristic of matter that can be observed or measured without changing the sample's composition - for example, density, color, taste, hardness, and melting point.

extensive property

A physical property, such as mass, length, and volume, that is dependent upon the amount of substance present.

intensive property

A physical property that remains the same no matter how much of a substance is present.

chemical property

The ability or inability of a substance to combine with or change into one or more new substances.

states of matter

The physical forms in which all matter naturally exists on Earth - most commonly as a solid, a liquid, or a gas.

solid

A form of matter than has its own definite shape and volume, is incompressible, and expands only slightly when heated.

liquid

A form of matter than flows, has constant volume, and takes the shape of its container.

gas

A form of matter than flows to conform to the shape of its container, fills the container's entire volume, and is easily compressed.

physical change

A type of change that alters the physical properties of a substance but does not change its composition.

chemical change

A process involving one or more substances changing into new substances; also called a chemical reaction.

law of conservation of mass

States that mass is neither created nor destroyed during a chemical reaction but is conserved.

mixture

A physical blend of two or more pure substances in any proportion in which each substance retains its individual properties; can be separated by physical means.

heterogeneous mixture

One that does not have a uniform composition and in which the individual substances remain distinct.

homogeneous mixture

One that has a uniform composition throughout and always has a single phase; also called a solution.

solution

A uniform mixture that may contain solids, liquids, or gases; also called a homogeneous mixture.

filtration

A technique that uses a porous barrier to separate a solid from a liquid.

distillation

A technique that can be used to physically separate most homogeneous mixtures based on the differences in the boiliing points of the substances involved.

crystallization

A separation technique that produces pure solid particles of a substance from a solution that contains the dissolved substance.

chromatography

A technique that is used to separate the components of a mixture based on the tendency of each component to travel or be drawn across the surface of another material.

element

A pure substance that cannot be broken down into simpler substances by physical or chemical means.

periodic table

A chart that organizes all known elements into a grid of horizontal rows (periods) and vertical columns (groups or families) arranged by increasing atomic number.

compound

A chemical combination of two or more different elements; can be broken down into simpler substances by chemical means and has properties different from those of its component elements.

law of definite proportions

States that, regardless of the amount, a compound is always composed of the same elements in the same proportion by mass.

percent by mass

A percentage determined by the ratio of the mass of each element to the total mass of the compound.

law of multiple proportions

States that when different compounds are formed by the combination of the same elements, different masses of one element combine with the same mass of the other element in a ratio of small whole numbers.

vapor

Gaseous state of a substance that is a liquid or a solid at room temperature.