Ch 2 Atoms and Elements

Ch 2 Atoms and Elements - Ch 2 Atoms Elements(for exam just...

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Ch. 2 Atoms + Elements (for exam, just 2.2-2.9) A. Scanning Tunneling Microscopy (STM) a. Tip of it is actually 1-4 atoms, sends out electrical current (sensitive to distance so will Δ depending on distance b/w end of tip + surface); looking for tiny Δs in current to indicate Δs in distance b. Scans back + forth to give topographic map c. Could visualize atoms B. 2.2 Early Ideas about Building Blocks of Matter a. Leucippus + student Democritus in 5 th century BC 1 st proposed that matter was composed of small, indestructible particles a.i. theorized that matter was ultimately composed of small, indivisible particles they named atomos a.ii. Plato + Aristotle thought that matter had no smallest parts, and that diff substances were composed of various proportions of fire, air, earth and water b. 16 th century, Nicolaus Copernicus proposed that sun, not Earth, was center of universe b.i. next 200 years, Bacon, Kepler, Galileo, Boyle, Newton brought advacneasment so by early 1800s, John Dalton offered convincing evidence supporting early atomic ideas of Leucippus + Democritus C. 2.3 Modern Atomic Theory + Laws that led to it a. Law of Conservation of Mass —in a chemical rxn, matter is neither created nor destroyed a.i. mass of reactants = mass of products b. Law of Definite Proportions —all samples of a given compound, regardless of their source or how they were prepared, have same proportions of their constituent elements b.i. ratio is same for every sample b.ii. compounds have definite proportions of constituent elements b/c atoms that compose them occur in a definite ratio c. Law of Multiple Proportions —when 2 elements (A and B) form 2 diff compounds, masses of element B that combine with 1 gram of element A can be expressed as ratio of whole numbers c.i. ratio of masses will always be small whole numbers c.ii. diff between law of definite + multiple proportions: c.ii.1. law of definite proportions applies to 2 or more samples of same compound and states that ratio of one element to other will always be the same; law of multiple proportions applies to two different compounds containing same 2 elements (A and B) and states that the ratio of masses of A and B are a small whole-number ratio d. John Dalton + Atomic Theory d.i. atomic theory: d.i.1. each element is composed of tiny, indestructible particles called atoms
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d.i.2. all atoms of a given element have same mass and other properties that distinguish them from atoms of other elements d.i.3. atoms combine in simple, whole-number ratios to form compounds d.i.4. atoms of one element can’t change into atoms of another element; in chemical rxn, atoms only change the way that they are bound together with other atoms D. 2.4 Discovery of Electron a. Cathode Rays a.i.
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Ch 2 Atoms and Elements - Ch 2 Atoms Elements(for exam just...

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