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CHAPTER FOUR: THE STRUCTURE OF THE ATOM The Atom Smallest particle of an element that retains the properties of that element * made of much smaller particles * our concept is a result of generations of work Early atomic theory begins with... Democritus * 400 BC * Claimed the world was nothing but empty space and atoms "All matter is made of very small particles much too small to see." atomos: indivisible * different types of atoms = different sizes, shapes and movement = different types of properties * believed that atoms could not be created, destroyed or further divided. Aristotle *criticized Democritus* (384322 BC) *thought the world was made of "hyle" (continuous matter) *Did NOT believe in atoms *Thought all matter was continuous * He couldn't wrap his mind around the concept of empty space! Aristotle believed that matter is made of... But really, what did it matter what philosophers thought when they had no experimental data to support their ideas? Improved balances helped scientists accurately measure masses of elements and compounds. This lead to several laws: 1. Law of Conservation of Mass 2. Law of Definite Proportions 3. Law of Multiple Proportions Law of Conservation of Mass Mass is neither created nor destroyed during ordinary chemical reactions or physical changes 2H2O 100.00g 11.21g H H 2H2 + O2 O H 88.79g H O O H H H O H Antoinne LaVoisier Law of Definite Proportions Proust A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound H2O 2:1 Not to be confused with THE LAW OF MULTIPLE PROPORTIONS 2 or more different compounds can be composed of the same elements H2O vs H2O2 water vs. hydrogen peroxide CO vs carbon monoxide vs. carbon dioxide CO2 John Dalton * 1800's * Studied experiments of others * Came up with a feasible theory about atoms The Atom: smallest particle of an element that retains the properties of the element. Dalton's Atomic Theory 1. All matter is made of atoms. 2. All atoms of the same element are identical. 3. Atoms of different elements are not alike. 4. Atoms can combine in simple, whole number ratios to form compounds (Law of multiple proportions). 5. Atoms cannot be subdivided, created or destroyed. CO molecules on Pt Made with atomic force microscope Xe on nickel Scanning Tunneling Microscope Iron on copper Nanotechnology