The Scientific Method: Observations, Hypotheses, Tests, and Theories

1. The Scientific MethodThe Atomic TheoryClassification of Matter Dr. Yau (loosely based on Chap. 1.4, 1.5, 1.6 in Jespersen, Brady & Hyslop, 6th edition)

2. What is meant by the “Scientific Method?” The scientific method is a way to solve a problem or answer a question in science. One simplistic way to view this method is to think of it as being in 4 steps: • Observe • Hypothesize • Test • Form Theory

3. The Scientific Method • Observe (looking for a pattern in the observations) Note: Observations could be from someone else’s experiments. • Form a hypothesis (which is an educated guess to explain the pattern) • Test the hypothesis a) Design a test that would provide evidence that the hypothesis is correct. It MUST be reproducible. b) Run the test and analyze the results. • If proven correct, hypothesis becomes theory. If not, it must be revised, re-tested or discarded.

4. Scientific Theory A scientific theory is not “absolute.” With improvement in instrumentation and new discoveries, additional experimental data can render a theory to become questionable. We can never be absolutely sure that a theory is correct. Scientists MUST keep an open mind.

5. The Scientific Method is Cyclical Fig 1.2 p. 4 Observations suggest explanations, which suggest new experiments, which suggest new explanations, and so on.

6. What is a Scientific Law? It is a generalized summary of a large quantity of data and observations for which there is no exception. It differs from a hypothesis or a theory in that it does not attempt to explain the phenomenon. e.g. The scientist, Boyle, noticed that when a sample of gas is allowed to expand, its pressure decreases proportionally if the temperature is kept constant. He states that the pressure (P) of a gas is inversely proportional to its volume (V) at constant temperature (T): There is no attempt to explain why.

7. Theory vs. Scientific Law Boyle’s Law (previous slide) alone did not bring us to the theory, but together with other laws such as Charles’ Law, Gay-Lussac’s Law and Avogadro’s Law, scientists came up with the Kinetic Molecular Theory to explain the behavior of gases. A sample of gases is made of small particles that are very far apart and are in constant random motion. It is the collision of these particles on the walls of the container that creates pressure. When the V is small, there would be more collisions with the walls, and thus P is larger. When V is increased, the particles have more room to move and there are less collisions with the walls and P decreases.

8. Learning Check: Whenever we put a burning match to a piece of paper it will burn. Classify this statement. It is… • a hypothesis • a theory • a test • an observation • a scientific law • a conclusion Answer: #4 Why is it not a hypothesis or theory?

9. Dalton’s Atomic Theory Dalton’s Atomic Theory is based on three scientific laws: • Law of Conservation of Mass • Law of Definite Proportions • Law of Multiple Proportions (These comprise the “observations” in the Scientific Method, leading to the “hypothesis” and ultimately, the “theory.”

10. Dalton’s Atomic Theory • Matter is made of tiny indivisible particles called atoms. (from Greek word “atomos” meaning indivisible). • Atoms of an element are identical in mass & other properties. Atoms of different elements have different properties. • Compounds are made of atoms of different elements combined in a fixed ratio of small whole numbers. • In reactions, atoms are not destroyed or created but merely rearrange to form new cmpds. Why are some words in red????

11. What Is An Element? • Elements- substances that cannot be decomposed into simpler substances. • shown on the periodic table as symbols: “K” for potassium and “Na” for sodium There are around 118 known elements. around 92 are natural occurring around 26 are man-made

12. Models Helps Us Visualize Matter Elements are made of identical atoms, either singly or in groups.

13. e • diamond • graphite • lonsdaleite • (diamond formed when C meteorites hit the earth) • buckyball • C540(nested bucky) • C70 • amorphous C • single-walled carbon nanotube or bucky tube Allotropes of Carbon To keep it simple, we just write C for carbon as if it were monatomic.

14. Chemical Symbols for Elements Chemical Symbol • One or two letter symbol for each element name • First letter capitalized, second letter lower case Ex. C = carbon S = sulfur Ca = calcium Ar = argon Br = bromine H = hydrogen Cl = chlorine O = oxygen • Used to represent elements in chemical formulas Ex. Water = H2O Carbon dioxide = CO2 • Most based on English name • Some based on Latin or German names

15. Chemical Symbols for Elements Some are given a single letter (always capitalized): H, B, C, N etc. Some are given two letters (first letter is always capitalized, and the second letter is always in lower case): He, Li, Be etc. If you write two letters with both upper case you would be implying a compound (made of two elements). e.g. HF is the compound, hydrogen fluoride. and Hf is the element, hafnium.

16. e.g. Co is the element, cobalt. and CO is the compound, carbon monoxide. It is essential you learn not to capitalize both letters if you had meant to refer to an element. In giving the name of an element, do not capitalize the name unless it is at the beginning of a sentence. The name of an element is NOT a proper noun.

17. Examples of elements: C, Fe, Al, O2, N2, P4 Examples of compounds: CO2, C12H22O11, NaCl What do the subscripts mean? First we must examine the concept of "atoms." An atom is the smallest particle of an element. (Note: It can be broken down further but it would become a different element.) 17

18. HOMEWORK: Learn the names and symbols of elements. Quiz next period includes this type of question. Example: Give the name or symbol of the following: S = ________ Ti = ________ ___ = potassium ___ = sodium Note: It is not sulphur, but sulfur. titanium, not Titanium not P! What is P? not S!

19. Note that there are symbols in the periodic table with more than 2 letters. Which ones?? These are elements not yet named. Elements are usually named by the scientists who discovered/made them. Sometimes it is difficult to prove who discovered them first. Meanwhile they are given 3 letters: Uuu = unununium (Latin for 111) now named roentgenium (symbol = Rg) Uub = ununbium (Latin for 112) now named copernicium (symbol = Cn) Uut = ununtrium (Latin for 113) not formally named. 19

20. Some chemical names originated from Latin or German

21. diamond = carbon gold sulfur Elements Getting bored? Have some fun? Click here: http://www.privatehand.com/flash/elements.html

22. Elements You should have already learned (and still remember!) the names and chemical symbols for many of these elements. This semester you will be learning a few more. If you took CHEM 107 on the Catonsville Campus you would be familiar with the Nomenclature Tutorial for Prep Chem. This semester you will be using the one designated for Gen Chem. There will be frequent quizzes on sections of this Nomenclature Tutorial. Check the Assignment page for what the quizzes will cover. They will always be cumulative and may contain material other than nomenclature.

23. What are Compounds? Compounds are substances made of more than one element combined Mixtures can also be substances made of more than one element. e.g. Brass = Cu + Zn e.g. Bronze = Cu + Sn Why are these not “compounds?” There is more than one answer to this. Try to think up as many as you can. in a fixed ratio.

24. What Is A Compound? • Compounds - formed from two or more atoms of different elements combined in a fixed proportion • Have different characteristics than the elements that compose them • Can be broken down into elements by some chemical changes

25. Hydrogen peroxide Fixed Ratios in Compounds Water is composed of H and O in a fixed ratio of 2 to 1, (1:8 by mass). Hydrogen peroxide is composed of H and O in a ratio of 1:1, (1:16 by mass).

26. Fixed Ratios in Compounds Methane Methane is composed of C and H in a fixed ratio of 1 to 4.

27. Fixed Ratios in Compounds: Oleic Acid from Cow’s Milk C17H34O2 What does this tell you about Dalton’s Atomic Theory?

28. Classification of Matter Matter is either a pure substance or a mixture Mixtures may be separated into pure substances using physical means such as distillation, filtration, chromatography (You did all this in CH108!)

29. Separation by physical means: They are based on the difference in physical properties of the components. e.g. Filtration of sand from water (Difference in solubility) e.g. Distillation of water from salt water (Difference in boiling point) e.g. Distillation of crude oil into useful fractions. (Difference in boiling point) At the oil refineries, crude oil is heated and various fractions are collected at different temperatures based on their boiling points. 29

30. gas liquid Distillation Tower at the Oil Refinery Gases (methane, ethane, propane, butane) C1 to C4 hydrocarbons BP below 20C Gasoline (naphthas) (C5 to C12) BP 20-200C Kerosene (C12 to C15) BP 175-275C Crude Oil is vaporized Fuel Oil (Diesel) (C15 to C18) BP 250-400C Lubricating Oil (C18 to C20) BP above 350C Residue (asphalt) (more than C20) solid Heat Source Distillation is separation by physical means. 30

31. Classification of Matter Mixtures can be classified as homogeneous mixtures or heterogeneous mixtures.

32. Homogeneous Mixtures Homogeneous mixtures have the same properties throughout the sample. Solutionsare homogeneous mixtures. e.g. salt water, coffee (without the grind) e.g. Rubbing alcohol is a solution of isopropyl alcohol and water. It can be purchased as a 90% or 70% solution. Alloys are homogeneous mixtures of metals. e.g. Brass is a homog. mix of Cu and Zn e.g. Bronze is a homog. mix of Cu and Sn. We can have different % of Zn in brass, giving it a whiter or more orange color. But, within one sample, the percentage is the same.

33. Homogeneous Mixtures • Same properties throughout sample • Solution • Thoroughly stirred homogeneous mixture Ex. • Liquid solution • Sugar in water • Gas solution • Air • Contains nitrogen, oxygen, carbon dioxide & other gases • Solid solution • US 5¢ coin – Metal Alloy • Contains copper & nickel metals

34. Heterogeneous Mixtures Heterogeneous mixtures… • do not have a uniform composition within a sample • components often not of the same physical state • components are not miscible (do not mix) e.g. oil and water e.g. mixed nuts e.g. sand and sugar

35. Heterogeneous Mixtures • 2 or more regions of different properties • Solution with multiple phases • Separate layers Ex. • Salad dressing • Oil & vinegar • Ice & water • Same composition • 2 different physical states

36. Mixtures • mixtures consist of varying amounts of two or more elements or compounds • Homogeneous mixtures or “solutions”- have the same properties throughout the sample • Brass, tap water • Heterogeneous mixtures-consist of two or more phases • Salad dressing, Coca-Cola ™

37. Brass is pure. Natural peanut butter made only by crushing peanuts is pure. Because blood cells can be distinguished from plasma under a microscope, blood is a heterogeneous mixture. True False True False True False Learning Check: Pure or Mixture?

38. Elements and Compounds Pure substances are classified as elements or compounds. Compounds can be separated into elements only by chemical means and not physical means, such as electrolysis, thermal decomposition.

39. Separation by Chemical Means Electric current Sodium metal + chlorine gas Molten sodium chloride 2 NaCl (s) 2 Na (s) + Cl2(g) Compounds can be separated into elements by chemical menas: Decomposition by electrolysis: • Chemical reaction where 1 substance is broken down into 2 or more simpler substances by passing an electric current thru the sample. Ex.

40. Separation by Chemical Means Electric Current 2 H2O (s) 2 H2(s) + O2(g) Do not confuse this with the what happens when you boil water! Write the equation for what happens when you boil water:

41. Learning Check: Classification X X X X X X X X Why is NaCl not a molecule?

42. Metals, Nonmetals, And Metalloids

43. Why it matters whether an element is METAL or NONMETAL KNOW THIS WELL! Nonmetal + Nonmetal = Molecular cmpd (covalent bonds) Metal + Nonmetal = Ionic cmpd (ionic bonds) Metal + Metal = Alloy (homog.mixt.) So why table salt not made of molecules?

44. Learning Check How is table sugar classified? Table sugar is sucrose from sugar cane with the formula C12H22O11 A. element B. molecule C. compound D. ionic compound E. homogeneous mixture. F. heterogeneous mixture. G. pure substance Ans. B, C, G

45. Learning Check How is S8 classified? A. element B. molecule C. compound D. ionic compound E. homogeneous mixture F. heterogeneous mixture G. pure substance Ans. A, B, G

46. Learning Check How is chalk classified? Assume it is calcium carbonate. A. element B. molecule C. compound D. ionic compound E. homogeneous mixture. F. heterogeneous mixture. G. pure substance Ans. C, D, G

47. Learning Check Which of the following is/are molecular compounds? A. P2O5 (in match heads) B. SO2 (air pollutant from factories) C. Fool’s gold (pyrite: FeS2) Fool’s Gold D. H2S (gas produced from acid on fool’s gold, smells like rotten eggs) E. I2 Ans. A, B, D, E

48. We can now extend the Classification of Matter further.

49. MATTER Pure Substance Mixture Element Compound Homogen. Heterogen. Mixture Mixture atommolecule molecular ionic compound compound