2.7 Phase Changes

Explain the properties of molecular motion in terms of states or phases of matter. Recognize the crystalline structure of solids.

Study Guide

Explain each Concept

è Physical properties of matter can be observed without changing its identity.

è When a substance undergoes a physical change, its identity remains the same.

è A chemical change occurs when one or more substances are changed into new substances with different properties.

è Chemical properties describe a substance based on its ability to change into a new substance with different properties.

è The density (mass per unit volume) of a substance is always the same at a given pressure and temperature regardless of the size of the sample of the substance.

è The characteristic properties of a substance are always the same whether the sample observed is large or small.

è Energy is needed to remove electrons from metal atoms to form positive ions.

è Energy is released when most nonmetal atoms gain electrons to form negative ions.