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Name: Date: Hour: Guided notes: Part II: History of the atomic theory I. General atom info: A. Atoms are fantastically durable. Because they last so long, atoms really get around! B. Every atom you possess has almost certainly passed through several _________and been part of millions of ______________ on its way to becoming you. C. Nowadays, with the use of _____________ electron microscopes, we can sort of “see” atoms… These electron microscopes were invented in the mid-1900’s. How did scientists _______________ _____ atomic structure without being able to look at any atoms? II. Development of atomic theory A. What is a theory in science? A theory is a well-tested explanation of what happens in nature. In layman’s terms, if something is said to be “just a theory,” it usually means that it is a mere _________, or is unproven. But in scientific terms, a theory implies that something has been _________________ and ______________ many times by _______________________ groups of scientists. A scientific law is a statement of something that seems to be _______ in the natural world. Example: The Law of Gravity. Newton could use this law to predict the behavior of a dropped object, but he couldn't ____________ why it happened. A law states or describes __________ happens in nature. A theory explains _______ it happens. Both are well-tested by _______________. Memory hint: “explanation starts with an “____” and “___________” has an “e”. III. Important Historical Figures A. Democritus • first to suggest that matter is made of tiny particles called “__________” • • • “atomos” = Greek for “______________________” ideas were rejected by ____________, who was very influential, and therefore forgotten for two thousand years. ancient Greek _______________, not scientist Democritus’ atomic model: atoms were small, hard particles that were different ___________ and _______ C. John Dalton: First to propose an atomic theory based on __________: **You’ll need to know each of these four parts of his theory 1. Each element is composed of small ___________ called atoms. 2. All atoms of a given element are ______________*; the atoms of different elements are __________________. 3. Atoms are not ______________ or _____________ in chemical reactions. 4. ________________ are formed when atoms of more than one element __________. Dalton’s atomic model: a tiny ____________ that is ________________ D. J.J. Thompson • First to suggest that there were particles ____________ than the atom. • Discovered the ______________. • Developed the “plum pudding model.” Thomson’s “plum-pudding” model: the atom is composed of electrons surrounded by a _____________of _____________ charge to ______________ the electron's negative charge E. Ernest Rutherford • __________ foil experiment • discovered the ____________, and realized that it was very ________ and _______________ charged • suggested that most of the atom is empty _____________ Gold Foil Experiment: Rutherford shot tiny positively-charged __________ particles through a thin sheet of gold foil Gold Foil Experiment: Some of the alpha particles _________________ ___________. “It was as if you fired a 15-inch cannon ball at a piece of tissue paper and it came back and hit you.” Such huge __________________ could mean only one thing: some of the alpha particles had run into massive concentrations of ___________ charge and, since like charges _____________ had been hurled straight back by them Rutherford’s atomic model: All of the positive charge is crammed inside a tiny, massive ___________about ______ __________________ times smaller than the atom as a whole. The atom is mostly empty _______________. F. James Chadwick • Scientists were looking for missing ______ – the ___________ and ____________ in the atom didn’t __________ enough to account for the mass of the atom proved the existence of _____________ • • Protons and neutrons are in the ____________, which only takes up one _______________ of a ______________ of the volume of the atom. The electrons are in the electron __________, which constitutes almost all of the volume of the atom. In fact, if an atom were expanded to the size of a cathedral, the nucleus would be about the size of a _____________