Acid - pH of less than 7 Base - pH of more than 7 pH - scale used to classify solutions Catalyst - substance that increases the rate of a chemical reaction Chemical change - result in the formation of one or more new substances with new chemical and physical properties Chemical properties - be recognized only when substances react or do not react chemically with one another, that is, when they undergo a change in composition. Compound - pure substances that are composed of two or more types of elements that are chemically combined Electrons - a negatively charged subatomic particle found outside of the nucleus of the atom Law of conservation of mass - The amount of matter does not change during a chemical reaction, only that the atoms are rearranged to form new substances. This is evidenced in a balanced chemical equation. Metal - elements with similar properties found on the left side of the “staircase” on the periodic table Metalloid - elements with similar properties that create a “staircase” on the periodic table Mixture - physical combinations of two or more different substances that retain their own individual properties and are combined physically (mixed together) Heterogeneous Mixture - is not uniform throughout, the component substances can be visibly distinguished Homogeneous Mixture - is uniform throughout, the substances are evenly mixed and cannot be visibly distinguished Neutrons - a subatomic particle with no charge (neutral) found in the nucleus of the atom. Nonmetal - elements with similar properties found on the right side of the “staircase” on the periodic table Periodic table - a quick reference for associating the name and symbol of an element. Physical change - do not change the composition of a substance, only the physical properties Physical properties - can be observed and measured without changing the kind of matter being studied. Precipitate - a solid substance formed when two solutions are chemically combined. Products - new substances formed in a chemical reaction and that they are located on the right side of the arrow in a chemical equation. Protons - a positive subatomic particle found in the nucleus of an atom. Reactants - substances broken apart or combined in a chemical reaction and that they are located on the left side of the arrow in a chemical equation