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Basics Of Chemistry 8th Science 2012 Matter Defined ► Matter – anything that has volume or mass. ► Everything you see and don’t see. Definitions ► Element- pure substance that cannot be separated into simpler substances by physical or chemical means. Represented by a symbol – Au stands for what? Definitions ► Atom – Smallest particle into which an element can be divided and still be the same substance, retaining its properties Evolution of the Atomic Theory ► Democritis – 440 BC ► Greek philosopher who said that if you cut a substance in half again and again and again eventually you would have an “uncuttable” piece said that all atoms made of a single material formed into different shapes and they join together to make different materials ► ► Greek word atomos, which means “indivisible” John Dalton - 1803 ► Studied the atmosphere and other gases and developed atomic theory. ► Dalton demonstrated that elements combine in specific proportions to make different substances John Dalton’s Atomic Theory Dalton’s New System of Chemical Philosophy ► 1. All substances are made of atoms. ► 2. Atoms are small particles that cannot be created, divided, or destroyed. Dalton’s Atomic Theory, continued ► 3. Atoms of the same element are identical in size, mass and other properties. ► 4. Atoms of different elements combine to make chemical compounds. ► 5. In chemical reactions, atoms are combined, separated, or rearranged. J.J. Thomson - 1897 ► discovered that there are small particles inside the atom, so the atom can be divided into smaller parts JJ Thomson, continued ► Experimented, using a cathode-ray tube to discover negative particles he called corpuscles negatively charged particles found in all atoms are now called electrons ► these Thomson’s Model ► Plum Pudding model ► Described electrons as scattered all about the atom Ernest Rutherford - 1908 Rutherford, continued ► Discovered a tiny, extremely dense, positively charged region called a nucleus ► Most of the atom’s mass was in the nucleus and electrons traveled around the nucleus Rutherford cont’d ► said the atom was mostly empty space Niels Bohr – 1913 ► said the electrons travel around the nucleus in definite paths Erwin Schrödinger and Werner Heisenberg - 1926 ► Said electrons travel in clouds, not definite paths but we still use the Bohr Model to represent atoms. The Atom Subatomic Particles Protons Determine the identity of the matter ► positively charged particles ► found in the nucleus ► Mass =1.67262158 × 10-27 kilograms 0.000000000000000000000000017 kg ► Each proton is 1 amu AMU stands for Atomic Mass Unit Subatomic Particles Neutrons Neutrons are the glue that holds the protons together in the nucleus ► ► ► no charge found in the nucleus mass is 1 amu Subatomic Particles Electrons Determine the reactivity ► Negatively charged ► Found around the nucleus within electron clouds ► Mass is very small, almost zero Atoms are NEUTRAL ► Atoms are neutral because the number of protons equals the number of electrons. How To Read a Square ► 8 ► O ► ► Oxygen 15.9994 ► Elements are identified by their atomic number – the number of protons. Also equals the number of electrons. ► Chemical Symbol ► Element Name ► Atomic Mass PEN Method ► SLIDE, SLIDE, ROUND THE BOTTOM SUBTRACT TOP ►P = 8 ►E = 8 ►N = 8 ► 8 ► O ► ► Oxygen 15.9994