Science Vocab

Term Definition
matter anything that has mass and takes up space
element a substance that cannot be separated or broken down into simpler substances by chemical means; all atoms of an element have the same atomic number
atom the smallest unit of an element that maintains the chemical properties of that element
molecule a group of atoms that are held together by chemical forces; a molecule is the smallest unit of matter that can exist by itself and retain all of a substance’s chemical properties (47)
compound a substance made up of atoms of two or more different elements joined by chemical bonds
pure substance a sample of matter, either a single element or a single compound, that has definite chemical and physical properties
mixture a combination of two or more substances that are not chemically combined
melting point the temperature and pressure at which a solid becomes a liquid
boiling point the temperature and pressure at which a liquid becomes a gas
density the ratio of the mass of a substance to the volume of the substance; commonly expressed as grams per cubic centimeter for solids and liquids and as grams per liter for gases
reactivity the capacity of a substance to combine chemically with another substance
physical change a change of matter from one form to another without a change in chemical properties
chemical change a change that occurs when one or more substances change into entirely new substances with different properties

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