Ch1 - Welcome to the World of Chemistry The Language of...

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Unformatted text preview: Welcome to the World of Chemistry The Language of Chemistry • CHEMICAL ELEMENTS - – pure substances that cannot be decomposed by ordinary means to other substances. The Language of Chemistry • The elements, their names, and symbols are given on the PERIODIC TABLE Aluminum Bromine Sodium The Periodic Table Glenn Seaborg (1912-1999 ) • Discovered 8 new elements. • Only living person for whom an element was named. Dmitri Mendeleev (1834 - 1907) • How many elements are there? • An atom is the smallest particle of An atom is an element that has the chemical properties of the element. Copper atoms on silica surface. See CDROM Screen 1.4 Distance across = 1.8 nanometer (1.8 x 10 -9 m) Page 1 The Atom CHEMICAL COMPOUNDS are are An atom consists of a • nucleus –(of protons and neutrons) (of protons neutrons • electrons in space about the nucleus. Electron cloud Nucleus composed of atoms and so can be decomposed to those atoms. MOLECULAR FORMULA The red compound is composed of • nickel ( Ni) (silver) nickel (Ni) • carbon (C) (black) carbon • hydrogen (H) (white) • oxygen (O) (red) oxygen • nitrogen (N) (blue) nitrogen The Nature of Matter Graphite — Gold A MOLECULE is the smallest unit of MOLECULE is a compound that retains the chemical characteristics of the compound. Composition of molecules is given by a layer structure of carbon atoms reflects physical properties. Mercury Chemists are interested in the nature of matter and how this is related to its atoms and molecules. Page 2 H2O C8H10N4O2 - caffeine Chemistry & Matter • We can explore the MACROSCOPIC world — what we MACROSCOPIC world can see — • to understand the PARTICULATE to PARTICULATE worlds we cannot see. • We write SYMBOLS to describe We SYMBOLS these worlds. A Chemist’s View of Water A Chemist’s View Macroscopic Macroscopic Symbolic Symbolic STATES OF MATTER • SOLIDS — have rigid shape, fixed have volume. External shape can reflect the atomic and molecular arrangement. – Reasonably well understood. • LIQUIDS — have no fixed shape and have may not fill a container completely. – Not well understood. • GASES — expand to fill their expand Matter consists of atoms and molecules in motion. Macroscopic Macroscopic H2O (gas, liquid, solid) Particulate Particulate Kinetic Nature of Matter Particulate Particulate 2 H2(g) + O2 (g) --> 2 H 2O(g) Symbolic Symbolic Physical Properties What are some physical properties? • color • melting and boiling point • odor container. – Good theoretical understanding. Page 3 Physical Changes Some physical changes Some physical would be • boiling of a liquid • melting of a solid • dissolving a solid in a liquid to give a homogeneous mixture — a SOLUTION. DENSITY - an important Relative Densities of the Elements and useful physical property Density = Mercury Problem A piece of copper has a mass of 57.54 g. It is 9.36 cm long, 7.23 cm wide, and 0.95 mm thick. Calculate density (g/cm 3). mass (g) volume (cm 3) Density = Platinum mass (g) volume (cm3) Aluminum 13.6 g/cm3 21.5 g/cm3 2.7 g/cm 3 Strategy SOLUTION 1. Get dimensions in common units. 1. Get dimensions in common units. 1cm 0.95 mm • = 0 .095 cm 10 mm 2. Calculate volume in cubic centimeters. 2. Calculate volume in cubic centimeters. (9.36 cm)(7.23 cm)(0.095 cm) = 6.4 cm 3 3. Calculate the density. 3. Note only 2 significant figures in the answer! Calculate the density. 57.54 g 6.4 cm3 = 9 .0 g/cm 3 Page 4 DENSITY • Density is an INTENSIVE property of matter. – does NOT depend does NOT on quantity of matter. – temperature • Contrast with EXTENSIVE – depends on quantity of matter. – mass and volume. Styrofoam Brick PROBLEM: Mercury (Hg) has a density PROBLEM: Mercury (Hg) has a density of 13.6 g/cm 33. What is the mass of 95 mL of 13.6 g/cm . What is the mass of 95 mL of Hg in grams? In pounds? of Hg in grams? In pounds? Solve the problem using DIMENSIONAL Solve ANALYSIS. ANALYSIS. There’s more? Observations! PROBLEM: Mercury (Hg) has a density of PROBLEM: Mercury (Hg) has a density of 13.6 g/cm33. What is the mass of 95 mL of Hg? 13.6 g/cm . What is the mass of 95 mL of Hg? First, note that 1 First, cm3 = 1 mL cm Strategy 1. Use density to calc. mass (g) from Use calc volume. 2. Convert mass (g) to mass ( lb) Need to know conversion factor = 454 g / 1 lb 454 lb Chemical Properties and Chemical Change •Burning hydrogen (H 2) in oxygen (O2) gives H2O. • Chemical change or Chemical or chemical reaction — transformation of one or more atoms or molecules into one or more different molecules. Page 5 PROBLEM: Mercury (Hg) has a density of PROBLEM: Mercury (Hg) has a density of 13.6 g/cm33. What is the mass of 95 mL of Hg? 13.6 g/cm . What is the mass of 95 mL of Hg? 1. Convert volume to mass 95 cm 3 • 2. 13.6 g cm3 = 1 .3 x 103 g Convert mass (g) to mass ( lb) 1.3 x 103 g • 1 lb = 2.8 lb 454 g Types of Observations and Measurements • We make QUALITATIVE We QUALITATIVE observations of reactions — changes in color and physical state. • We also make QUANTITATIVE We QUANTITATIVE MEASUREMENTS , which involve numbers . • Use SI units — based on the Use SI metric system UNITS OF MEASUREMENT Use SI units — based on the Use SI metric system Units of Length • 1 kilometer (km) = ? meters (m) • 1 meter (m) = ? centimeters (cm) • 1 centimeter (cm) = ? millimeter (mm) Length Length Meter, m Mass Mass Kilogram, kg Time Seconds, s Temperature Celsius degrees, ˚C kelvins , K Fahrenheit Celsius O—H distance = O—H distance = -11 9.4 x 10-11 m 9.4 x 10-11 m -9 9.4 x 10-9 cm 9.4 x 10-9 cm cm 0.094 nm 0.094 nm Temperature Scales Kelvin 212 ˚F 100 ˚C 373 K 180˚F Freezing point of water 100˚C 32 ˚F 0 ˚C • Fahrenheit • Celsius • Kelvin • 1 nanometer (nm) = 1.0 x 10-9 meter Temperature Scales Boiling point of water Temperature Scales 100 oF 38 oC 311 K 100 K 273 K Anders Celsius 1701-1744 Lord Kelvin (William Thomson) 1824-1907 Calculations Using Temperature •• Generally require temp’s in kelvins Generally require temp’s in kelvins kelvins • T (K) = t (˚C) + 273.15 • T (K) = t (˚C) + 273.15 •• Body temp = 37 ˚C + 273 = 310 K Body temp = 37 ˚C + 273 = 310 K Notice that 1 kelvin degree = 1 degree Celsius oF oC K Page 6 •• Liquid nitrogen = -196 ˚C + 273 = 77 K Liquid nitrogen = -196 ˚C + 273 = 77 K ...
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This note was uploaded on 10/19/2011 for the course CHM 2210 taught by Professor Romanmanetsch during the Summer '08 term at University of South Florida - Tampa.

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