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 Sodium Bromine • How many elements are there? The Periodic Table Glenn Seaborg (1912-1999 ) • Discovered 8 new elements. • Only living person for whom an element was named. • An atom is the smallest particle of atom is an element that has the chemical properties of the element. Copper atoms on silica surface. See CDROM Screen 1.4 Dmitri Mendeleev (1834 - 1907) Distance across = 1.8 nanometer (1.8 x 10 -9 m) Page 1 The Atom An atom consists of a CHEMICAL COMPOUNDS are are composed of atoms and so can be decomposed to those atoms. • nucleus –(of protons and neutrons) neutrons) • electrons in space about the nucleus. Electron cloud 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 MOLECULAR FORMULA H2O Nucleus The red compound is composed of • nickel (Ni) (silver) (Ni) (Ni) • carbon (C) (black) • hydrogen (H) (white) • oxygen (O) (red) • nitrogen (N) (blue) C8H10N4O2 - caffeine caffeine The Nature of Matter Graphite — Gold Mercury Chemistry & Matter • We can explore the MACROSCOPIC world — what we can see — • to understand the PARTICULATE worlds we cannot see. • We write SYMBOLS to describe these worlds. layer structure of carbon atoms reflects physical properties. Chemists are interested in the nature of matter and how this is related to its atoms and molecules. Page 2 A Chemist’s View of Water A Chemist’s View Kinetic Nature of Matter Matter consists of atoms and molecules in motion. Macroscopic Macroscopic H2O (gas, liquid, solid) Particulate Particulate Symbolic Symbolic Particulate Particulate Macroscopic Macroscopic 2 H2(g) + O2 (g) --> 2 H 2O(g) Symbolic Symbolic • SOLIDS — have rigid shape, fixed have STATES OF MATTER volume. External shape can reflect the atomic and molecular arrangement. – Reasonably well understood. Physical Properties What are some physical properties? • color • melting and boiling point • odor Physical Changes Some physical changes would be • boiling of a liquid • melting of a solid • dissolving a solid in a liquid to give a homogeneous mixture — a SOLUTION. • LIQUIDS — have no fixed shape and have may not fill a container completely. – Not well understood. • GASES — expand to fill their expand container. – Good theoretical understanding. Page 3 DENSITY - an important an and useful physical property Density = mass (g) volume (cm 3) Platinum Aluminum Relative Densities of the Elements Problem A piece of copper has a mass piece of 57.54 g. It is 9.36 cm long, 7.23 cm wide, and 0.95 mm thick. Calculate density (g/cm 3). Density = Mercury mass (g) volume (cm3) 13.6 g/cm3 21.5 g/cm3 2.7 g/cm 3 Strategy 1. Get dimensions in common units. SOLUTION 1. Get dimensions in common units. 1cm 0.95 mm • = 0 .095 cm 10 mm 2. Calculate volume in cubic centimeters. DENSITY • Density is an INTENSIVE property property of matter. – does NOT depend NOT on quantity of matter. – temperature • Contrast with EXTENSIVE – depends on quantity of matter. – mass and volume. Styrofoam Brick 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 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? 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 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? cm3 = 1 mL cm mL 1. Convert volume to mass Solve the problem using DIMENSIONAL DIMENSIONAL ANALYSIS. Strategy 1. Use density to calc. mass (g) from calc. volume. 2. Convert mass (g) to mass (lb) (lb) Need to know conversion factor = 454 g / 1 lb 95 cm 3 • 2. 13.6 g cm3 = 1 .3 x 103 g Convert mass (g) to mass (lb) (lb) 1.3 x 103 g • 1 lb = 2.8 lb 454 g There’s more? Observations! Chemical Properties and Chemical Change •Burning hydrogen (H 2) in oxygen (O2) gives H2O. • Chemical change or chemical reaction — transformation of one or more atoms or molecules into one or more different molecules. Types of Observations and Measurements • We make QUALITATIVE observations of reactions — changes in color and physical state. • We also make QUANTITATIVE MEASUREMENTS , which involve numbers . • Use SI units — based on the metric system Page 5 UNITS OF MEASUREMENT Use SI units — based on the metric system Length Mass Time Temperature Meter, m Kilogram, kg Seconds, s Celsius degrees, ˚C kelvins, K kelvins, Units of Length • 1 kilometer (km) = ? meters (m) • 1 meter (m) = ? centimeters (cm) • 1 centimeter (cm) = ? millimeter (mm) • 1 nanometer (nm) = 1.0 x 10-9 meter (nm) meter O—H distance = O—H distance = 9.4 x 10-11 m 9.4 x 10-11 m 9.4 x 10-9 cm 9.4 x 10-9 cm cm 0.094 nm 0.094 nm Temperature Scales • Fahrenheit • Celsius • Kelvin Anders Celsius 1701-1744 Lord Kelvin (William Thomson) 1824-1907 Temperature Scales Fahrenheit Boiling point of water Celsius 100 ˚C 100˚C 0 ˚C Kelvin 373 K 100 K 273 K Temperature Scales 100 oF 38 oC 311 K Calculations Using Temperature •• Generally require temp’s in kelvins Generally require temp’s in kelvins kelvins 212 ˚F 180˚F Freezing point of water 32 ˚F • 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 •• Liquid nitrogen = -196 ˚C + 273 = 77 K Liquid nitrogen = -196 ˚C + 273 = 77 K Notice that 1 kelvin degree = 1 degree Celsius oF oC K Page 6 ...
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This note was uploaded on 01/11/2011 for the course ENGINEERIN MAE 107 taught by Professor Pozikrizdis during the Fall '08 term at San Diego.

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