Chemistry

1. Chemistry Dr Seemal jelani

2. Dr Seemal jelani The Language of Chemistry Pure substances cannot be decomposed by ordinary means to other substances. Aluminum Sodium Bromine

3. Dr Seemal jelani The Language of Chemistry • The elements, their names, and symbols are given on thePERIODIC TABLE • How many elements are there? • 117 elements have been identified • 82 elements occur naturally on Earth • Examples: gold, aluminum, lead, oxygen, carbon • 35 elements have been created by scientists • Examples: technetium, americium, seaborgium

4. Measurements in chemistry Dr Seemal jelani

5. Dr Seemal jelani Types of Observations and Measurements • We makeQUALITATIVEobservations of reactions — changes in color and physical state. • We also makeQUANTITATIVE MEASUREMENTS, which involve numbers. • UseSI units— based on the metric system

6. Dr Seemal jelani Metric Prefixes • Kilo- means 1000 of that unit • 1 kilometer (km) = 1000 meters (m) • Centi- means 1/100 of that unit • 1 meter (m) = 100 centimeters (cm • Milli- means 1/1000 of that unit • 1 Liter (L) = 1000 milliliters (mL)

7. Dr Seemal jelani Metric Prefixes

8. O—H distance = 9.4 x 10-11 m 9.4 x 10-9 cm 0.094 nm Dr Seemal jelani Units of Length • 0.5 kilometer (km) = 500 meters (m) • 2.5 meter (m) = 250 centimeters (cm) • 1 centimeter (cm) = 100 millimeter (mm) • 1 nanometer (nm) = 1.0 x 10-9 meter

9. Dr Seemal jelani Learning Check Select the unit you would use to measure 1. Your height a) millimeters b) meters c) kilometers 2. Your mass a) milligrams b) grams c) kilograms 3. The distance between two cities a) millimeters b) meters c) kilometers 4. The width of an artery a) millimeters b) meters c) kilometers

10. Anders Celsius 1701-1744 Lord Kelvin (William Thomson) 1824-1907 Dr Seemal jelani Temperature Scales • Fahrenheit • Celsius • Kelvin

11. 212 ˚F 100 ˚C 373 K 100 K 180˚F 100˚C 32 ˚F 0 ˚C 273 K Dr Seemal jelani Temperature Scales Fahrenheit Celsius Kelvin Boiling point of water Freezing point of water Notice that 1 kelvin = 1 degree Celsius

12. Dr Seemal jelani 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

13. Always estimate ONE place past the smallest mark! Dr Seemal jelani

14. TEMPERATURE Dr Seemal jelani

15. Dr Seemal jelani SCALES • Kelvin • Fahrenheit • Celsius

16. Dr Seemal jelani Conversions • To Celsius • To Kelvin • To Fahrenheit

17. Dr Seemal jelani • °C  x  9/5 + 32 = °F • (°F  -  32)  x  5/9 = °C

18. Dr Seemal jelani Examples • 1)  Convert 37°C to Fahrenheit. 37°C x  9/5 + 32 = 98.6°F

19. Dr Seemal jelani • Convert 98.6°F to Celsius. (98.6°F  -  32)  x  5/9 = 37°C

20. Platinum Mercury Aluminum Dr Seemal jelani DENSITY - an important and useful physical property 13.6 g/cm3 21.5 g/cm3 2.7 g/cm3

21. Dr Seemal jelani • Density often has units of grams per cubic centimeter (g/cm3). • Remember, grams is a mass and cubic centimeters is a volume (the same volume as 1 milliliter).

22. Dr Seemal jelani • Density is a fundamental concept in the sciences • It is used quite often in identifying rocks and minerals since the density of substances rarely changes significantly • For example, gold will always have a density of 19.3 g/cm3; if a mineral has a density other than that, it isn't gold.

23. Dr Seemal jelani How do I determine density? • A concrete cube will weigh more than a cube of air the same size because it is denser • Density is not something that is directly measured. Typically if you want to know the density of something you will weigh it and then measure its volume.

24. Dr Seemal jelani • Another tricky thing about density is that you can't add densities • If I have a rock that is made up of two minerals, one with a density of 2.8 g/cm3, and one with a density of 3.5 g/cm3, the rock will have a density between 3.5 and 2.8 g/cm3, not a density of 6.3 g/cm3 • This is because both the mass and the volume of the two minerals will be added, and so when they are divided to get the density the result will be between the two.

25. Dr Seemal jelani • Typical densities for gasses are on the order of thousandths of grams per cubic centimeter • Liquids often have densities of about 1.0 g/cm3, and indeed, fresh water has a density of 1.0 g/cm3 • Rocks often have a density around 3 g/cm3, and metals often have densities above 6 or 7 g/cm3.

26. Dr Seemal jelani ProblemA 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).

27. Dr Seemal jelani Strategy 1. Get dimensions in common units. 2. Calculate volume in cubic centimeters. 3. Calculate the density.

28. Dr Seemal jelani 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!

29. Dr Seemal jelani Solution 2) Placing the mass and volume of the osmium metal into the density setup, we obtain D = mass = 50.00 g = volume 2.22 cm3 = 22.522522 g/cm3 =22.5 g/cm3

30. Dr Seemal jelani Scientific Method • State the problem clearly. • Gather information. • Form a hypothesis.. • Test the hypothesis. • Evaluate the data to form a conclusion. If the conclusion is valid, then it becomes a theory. If the theory is found to be true over along period of time (usually 20+ years) with no counter examples, it may be considered a law. 6. Share the results.