HiSET Science: Chemical and Physical Properties and Changes

Chemical and Physical Properties
Matter has both physical and chemical properties. Physical properties can be seen or observed without changing the identity or composition of matter. For example, the mass, volume, and density of a substance can be determined without permanently changing the sample. Other physical properties include color, boiling point, freezing point, solubility, odor, hardness, electrical conductivity, thermal conductivity, ductility, and malleability.
Chemical properties cannot be measured without changing the identity or composition of matter. Chemical properties describe how a substance reacts or changes to form a new substance. Examples of chemical properties include flammability, corrosivity, oxidation states, enthalpy of formation, and reactivity with other chemicals.

Intensive and Extensive Properties
Physical properties are categorized as either intensive or extensive. Intensive properties do not depend on the amount of matter or quantity of the sample. This means that intensive properties will not change if the sample size is increased or decreased. Intensive properties include color, hardness, melting point, boiling point, density, ductility, malleability, specific heat, temperature, concentration, and magnetization.
Extensive properties do depend on the amount of matter or quantity of the sample. Therefore, extensive properties do change if the sample size is increased or decreased. If the sample size is increased, the property increases. If the sample size is decreased, the property decreases. Extensive properties include volume, mass, weight, energy, entropy, number of moles, and electrical charge.

Atomic Properties of Neutral Atoms, Anions, and Cations
Neutral atoms have equal numbers of protons and electrons. Cations are positively-charged ions that are formed when atoms lose electrons in order to have a full outer shell of valence electrons.
For example, the alkali metals sodium and potassium form the cations Na+ and K+, and the alkaline earth metals magnesium and calcium form the cations Mg2+ and Ca2+.
Anions are negatively-charged ions that are formed when atoms gain electrons to fill their outer shell of valence electrons. For example, the halogens fluorine and chlorine form the anions F– and Cl–.

Chemical and Physical Changes
Physical changes do not produce new substances. The atoms or molecules may be rearranged, but no new substances are formed. Phase changes or changes of state such as melting, freezing, and sublimation are physical changes. For example, physical changes include the melting of ice, the boiling of water, sugar dissolving into water, and the crushing of a piece of chalk into a fine powder.
Chemical changes involve a chemical reaction and do produce new substances. When iron rusts, iron oxide is formed, indicating a chemical change. Other examples of chemical changes include baking a cake, burning wood, digesting food, and mixing an acid and a base.