Foundations, Atomic Structure, Stoichiometry

1. Foundations, Atomic Structure, Stoichiometry Unit 1

2. Significant Figures and Calculations Rules • Non zero digits are significant • A zero is significant if it is - “terminating AND right” of the decimal [must be both] - “sandwiched” between significant figures 3. Exact or counting numbers have an  amount of significant figures as do constants

3. Example 1 Give the number of significant figures for each of the following results. a. 0.010055 g b. 0.050080 g c. 8,500 mL d. 8.500 x 10-3 s

4. Rounding Rules • You can only be as accurate as your least accurate measurement.

5. Rounding Rules: • Round at the end of all calculations • Look at the significant figure one place beyond your desired number of significant figures if >5 round up; <5 drop the digit.

6. Example #2 Round the following values to the given number of significant figures. a. 8,543 g 3 sig figs b. 0.001378 2 sig figs c. 13,030 3 sig figs

7. Rules for calculating 1. x and  The term with the least number of significant figures determines the number of significant figures in the answer. 4.56 x 1.4 = ______ = rounded ______

8. 2. + and (-) The term with the least number of decimal places determines the number of significant figures in the answer. 12.11 + 18.0 + 1.013 = ____________ = rounded _________

9. Example #3 Round the following to the correct # of sig figs. • 32.2 m + 23.122 m + 22.2256 m = • 0.023 cm x 34.5 cm x 0.002 cm = • 99.356 g + 33.266 – 63.0932 = • 1.02 g / 100.0 mL =

10. e. A metal object has a mass of 4.5 grams. A graduated cylinder is filled with 15.43 mL of water. After the metal object is added to the graduated cylinder, the water level rises to the 17.56 mL mark. Calculate the density of the metal object.

11. Precision and Accuracy • - accuracy – how close the value is the accepted or correct value • - precision – how close the values are to each other

12. Example #4 • To check the accuracy of a graduated cylinder, a student filled the cylinder to the 25-mL mark using water delivered from a buret and then read the volume delivered. Following are the results of five trials: • Trial Volume Shown by Volume Shown • Graduated Cylinder by the Buret • 1 25 mL 26.54 mL • 2 25 mL 26.51 mL • 3 25 mL 26.60 mL • 4 25 mL 26.49 mL • 5 25 mL 26.57 mL • Average 25 mL 26.54 mL • Is the graduated cylinder accurate?

13. Units of Measurements • A quantitative measurement ALWAYS consists of two parts; a number and a unit • SI system – international agreement of units

14. MEMORIZE the following: Quantity, symbol Unit, abbrev. Length, l meter, m Mass, m kilogram, kg Temperature, T Kelvin, K Amt of substance, n mole, mol Time, t second, s Electric current ampere, A

15. ***1 cm3 = 1 mL

16. DIMENSIONAL ANALYSIS Must show the correct set up in the problems. You must KNOW your prefixes and factors!

17. Conversions you may need: • 1 m = 1.094 yd 2.54 cm = 1 in • 1 kg = 2.205 lb 453.6 g = 1 lb • 1 mi = 1760 yd 1 L = 1.06 qt

18. Example #5 • A student has entered a 10.0 km run. How long is the run in miles? • Convert 4.50 Mm to mm.

19. The speed limit on many highways in the US is 55 mi/hr. What number would be posted in kilometers per hour? • A Japanese car is advertised as having a gas mileage of 15 km/L. Convert this rating to miles per gallon. • Change 9.4 x 1012 cm3 to dL.

20. ATOMIC STRUCTURE • Elements – all matter with only one type of atom is an element.

21. Atoms – the smallest particle of an element that retains the chemical properties of that element.

22. Nucleus – the densest part of the atom, contains protons and neutrons, very small • Proton – positively charged, identifies the element • Neutron – no charge, about the same size and mass of a proton, responsible for isotopes

23. Electron – negative charge, the particle with the smallest mass, found outside the nucleus

24. Atomic Number(Z) = # protons, which identifies the element. Mass number (A) = # protons + # neutrons Element Symbol

25. The actual mass is not an integral number! Mass defect— this is related to the energy binding the particles of the nucleus together.

26. Example # 6 • Write the symbol for the atom that has an atomic number of 9 and a mass number of 19. How many electrons and how many neutrons does this atom have? • Determine the number of protons, neutrons, and electrons in a neon atom.

27. Isotopes Isotopes – atoms with the same number of protons (atomic number) but a different number of neutrons (different mass number) Hydrogen isotopes – the most common 0 neutrons  hydrogen 1 neutron  deuterium 2 neutron  tritium

28. Example #7 • Determine the number of protons, neutrons, electrons in an atom of carbon-14. • Determine the number of protons, neutrons, electrons in atom of tungsten.

29. 2.4 EARLY EXPTS. TO CHARATERIZE THE ATOM The Electron discovered by J.J. Thomson using the cathode ray experiment.

30. Ray was produced at the – electrode. • Attracted to the + pole of the electric field • Therefore, the ray was a stream of particles with a negative charge.

31. Plum Pudding Model Lord Kelvin

32. RADIOACTIVITY THREE types of radioactive emission: • alpha--equivalent to a helium nucleus; the largest particle radioactive particle emitted; 7300 times the mass of an electron.

33. beta, --a high speed electron. 3. Gamma --pure energy, no particles at all! Most penetrating, therefore, most dangerous. Symbols

34. Nucleus Gold Foil Experiment was led by Ernest Rutherford.

36. Results from Gold Foil Exp • Most of the alpha particles passed straight through • A few alpha particles scattered at a slight angle • Very few alpha particles were reflected right back

37. Conclusions from Gold Foil Exp • The center (nucleus) is very small and dense • The nucleus is positively charged and in the center of the atom

38. Classification of Matter • Solid – definite shape and volume, particles are close together and vibrate in place • Gas – indefinite shape and volume, particles are very far apart and move very fast, highly compressible

39. Liquid – indefinite shape and definite volume, particles are slightly far apart, slightly compressible • Vapor – a substance that is a solid or liquid at room temperature • Fluid – gas and liquids; particles that are far enough apart to slide past each other

40. Matter can be broken down into 2 broad categories: Pure substances and Mixtures. Mixtures – can be separated by a physical process

42. Homogeneous – a mixture that is the same throughout Heterogeneous – a mixture that has visibly distinguishable parts

43. Mixtures can be separated using the following means: • Distillation • Crystallization • Chromatography • Filtering

45. Pure substances – compounds like carbon dioxide, water, AND elements • Can only be separated using a chemical process like electrolysis

46. Molecules and Ions • Electrons are involved in forming bonds. • Chemical Bond – a force that holds elements together

47. 3 types of bonds: Covalent bond – involves sharing of electrons; occurs in molecules • Ionic bond – involves a transfer of electrons; occurs in ionic compounds • Metallic bond – involves positive ions surrounded by a sea of electrons; occurs in alloys

48. 3 types of compounds: • Molecule – a compound with only nonmetals • Ionic Compound – a compound with a metal and a nonmetal or a polyatomic • Alloy – a compound with 2 or more metals

49. Ions – an atom with a positive or negative charge • Cations  (+) ions; often metals since metals lose electrons to become + charged • Anions  (-) ions; often nonmetals since nonmetals gain electrons to become – charged

50. Molecular formula – uses symbols and subscripts to represent a compound; held by covalent bonds