STRUCTURE & CHANGES OF MATTER BASIC PRINCIPLES, CONCEPTS, AND TERMS I. All matter is composed of one or more substances (elements and/or compounds); compounds can be broken down into simpler substances: elements cannot be broken down chemically. II. All matter is composed of tiny particles, called atoms. A. Atoms of different elements are different. B. All atoms of one element are basically alike. 1. Atoms are basically electrical (are composed of electrically charged particles). 2. The mass of an atom is concentrated in its center (nucleus). 3. The size of an atom is 100,000 times larger than its nucleus. Visualize this: If an atom were the size of a big baseball stadium, its nucleus would be the size of a grain of sand!!! So, an atom is mostly empty space, with little fuzzy electrons whizzing by! a) The atomic nucleus has a positive charge, and is composed of protons & neutrons. b) Protons, each with positive charge, have about same mass as neutrons; Number of protons in atoms of each element is unique (= atomic no.). c) Neutrons, each with no charge, have about same size & mass as protons. Different numbers of neutrons in atom à different isotopes. d) Electrons, each with negative charge, “fly” around the atom at high speed. 1) There is considerable space between the nucleus and electrons. 2) All particles of the atom are in constant motion; the motion of electrons is most pronounced: they move in constantly changing, random orbits around the nucleus at high velocity, creating an "electron cloud". Gain or loss of electron(s) ---> ion(s). MATTER: Anything that has mass (“weight”) and takes up space. SUBSTANCE: Material composed of only one kind of matter throughout (same atoms or same molecules) ELEMENT: A substance that cannot be decomposed (broken down) into simpler substances by ordinary chemical means. Examples: gold, iron, carbon, hydrogen, oxygen, nitrogen. COMPOUND: A substance composed of two or more different elements chemically combined in definite proportions by mass. Examples: water, carbon dioxide, methane, ammonia. MIXTURE: Two or more substances which intermingle in any proportion without any chemical reaction taking place. (Not of uniform composition throughout, therefore, not a substance). Includes solutions, suspensions, emulsions, and alloys. ATOM: Smallest particle of an element that still has the properties of that element, and which can enter into combination with other elements; is composed of electrons, protons, and usually neutrons. MOLECULE: Smallest particle of a substance that has the properties of that substance (usually a compound); also, a particle composed of two or more atoms united by chemical bonds. PHYSICAL STATES OF MATTER: Solid, Liquid, Gas PHYSICAL CHANGE: Any change in matter that does not destroy the identity of a substance, nor change its characteristic chemical properties. Examples: 1. Changes of State: melting, evaporation, condensation, freezing, subliming 2. Physical Combination: mixtures, solutions, emulsions, suspensions, alloys 3. Physical Separation: distillation, centrifugation, screening, breaking, tearing, etc. CHEMICAL CHANGE: Any change of matter that results in the identity of the original substance or substances being lost, and the new substance or substances with new properties being produced; this involves only the outermost "shell" or "energy level" of electrons. Examples: 1. Combining Reactions: burning, rusting, tarnishing, synthesis 2. Decomposing Reactions: decay, hydrolysis, electrolysis, etc.