Welcome to the World of Chemistry

Welcome to the World of Chemistry : Welcome to the World of Chemistry Yale University Chemistry 113 Fall 2006: Prof. Victor S. Batista Spring 2007: Prof. Gary W. Brudvig

What does Chemistry concern with ? : What does Chemistry concern with ? WHAT MATTER IS ? HOW CAN MATTER BE MADE ? HOW DOES MATTER BEHAVE ? Chemistry is the foundation of all molecular sciences Chemistry provides understanding, prediction and control of the nature and behavior of matter Chemistry is practical and profoundly philosophical

Chemistry & Matter : Chemistry & Matter We can explore the MACROSCOPIC world — what we can see — to understand the PARTICULATE worlds we cannot see. We perform EXPERIMENTS to explore these worlds. (students are strongly encourage to take the lab 116L)

A Chemist’s View: Exp. I : A Chemist’s View: Exp. I 2 H2(g) + O2 (g) --> 2 H2O(g)

Chemical Properties and Chemical Change : Chemical Properties and Chemical Change Chemical change or chemical reaction — transformation of one or more atoms or molecules into one or more different molecules. Burning hydrogen (H2) in oxygen (O2) gives H2O.

A Chemist’s View: Exp. II : A Chemist’s View: Exp. II Zn(s) + S (s) --> ZnS(s)

Scientific Method : Scientific Method (1) Question about some aspect of the world. (2) Postulate a tentative explanation (hypothesis) and make predictions. (3) Test those predictions against observations of reproducible events. (4) Repeat steps 2 and 3 until there are no more discrepancies between predictions and observations. When consistency is obtained hypotheses become a coherent set of propositions (a theory) that explain a class of phenomena.

Types of Observations and Measurements : 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

UNITS OF MEASUREMENT : 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

Units of Length : 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 1 angstrom (A) = 1.0 x 10-10 meter o o

Temperature Scales : Temperature Scales Fahrenheit Celsius Kelvin

Temperature Scales : Temperature Scales Notice that 1 K degree = 1 degree Celsius Boiling point of water Freezing point of water Celsius Kelvin Fahrenheit

Temperature Scales : Temperature Scales 100 oF = 38 oC = 311 K oF oC K 38 oC = (100 oF – 32 oF) * 100 oC / 180 oF 311 K = 273 K + 38 oC * 100 K / 100 oC Conversion Factor: 100 oC degrees per 180 oF degrees 32 oF = 0 oC = 273 K

Calculations Using Temperature : Calculations Using Temperature Generally require temp’s in kelvins T (K) = t (˚C) + 273.15 Body temp = 37 ˚C + 273 = 310 K Liquid nitrogen = -196 ˚C + 273 = 77 K

Physical Properties : Physical Properties What are some physical properties? color melting and boiling point odor Physical properties characterize the identity of pure substances salt sodium

Physical Changes : 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. Physical changes do not change the identity of Pure Substances

DENSITY - an important and useful physical property : DENSITY - an important and useful physical property 13.6 g/cm3 21.5 g/cm3 2.7 g/cm3 Physical properties, cont’d

Slide18 : 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/cm3). Density = mass ( g ) volume ( cm 3 )

Slide19 : Strategy 1. Get dimensions in common units. 2. Calculate volume in cubic centimeters. 3. Calculate the density.

Slide20 : SOLUTION 1. Get dimensions in common units. 2. Calculate volume in cubic centimeters. 3. Calculate the density. (9.36 cm)(7.23 cm)(0.095 cm) = 6.4 cm3 Note only 2 significant figures in the answer! Conversion factor

Significant Figures : Significant Figures 57.54 g 4 significant figures 7.23 cm 3 significant figures 0.95 mm 2 significant figures 0.095 cm 2 significant figures (zeros to the left of 9 simply locate the decimal point) 600. g 3 significant figure 8000 kg 1 significant figure 100 cm/m infinte number of significant figures (defined quantity)

DENSITY : DENSITY Density is an INTENSIVE property of matter. does NOT depend on quantity of matter. temperature Contrast with EXTENSIVE depends on quantity of matter. mass and volume. Styrofoam Brick

PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg? : 1. Convert volume to mass PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg? 2. Convert mass (g) to mass (lb) Inverse Problems

PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg in grams? In pounds? : PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg in grams? In pounds? Solve the problem using DIMENSIONAL ANALYSIS.

PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg? : Strategy 1. Use density to calc. mass (g) from volume. 2. Convert mass (g) to mass (lb) Need to know conversion factor = 454 g / 1 lb PROBLEM: Mercury (Hg) has a density of 13.6 g/cm3. What is the mass of 95 mL of Hg? First, note that 1 cm3 = 1 mL