Chapter 2 (Part 1) Slides - Scientific Method and Chemistry PDF

Chapter 1 Any questions? Scientific Method Make an observation Ask a question Form a testable hypothesis Test hypothesis with an experiment Analyze data What affects the rate of diffusion? How to design an experiment What are you measuring? What is the control condition?...

Chapter 1 Any questions? Scientific Method Make an observation Ask a question Form a testable hypothesis Test hypothesis with an experiment Analyze data What affects the rate of diffusion? How to design an experiment What are you measuring? What is the control condition? What is the test condition? In other words, what is the variable you are changing? What is something that you think could cause humans to sweat? I hypothesize that ___________ will increase sweating. Design an experiment to test your hypothesis Experimental Design I hypothesize that ___________ will increase sweating. Experimental Group: Control Group: Dependent Variable: Independent Variable: What other variables will you need to control for? Scientific Article Introduction » Introduces what is known about the topic of interest. » Explains what question this experiment hopes to answer about that topic » Why it’s important Methods » Describes the procedures of the experiment Results » Describes the data and any trends seen in the data. Conclusions » Interprets the data. Proposes an explanation for what the results could mean. What do your results mean?  What is the trend? What is the interpretation? 98.51% correlation Does this data PROVE your interpretation is correct? Data sources: U.S. Census Bureau and National Science Foundation No, but it supports that interpretation. http://www.tylervigen.com/spurious-correlations  What is the trend? What is the interpretation? 99.26% correlation Does this data PROVE your interpretation is correct? No, but it supports that interpretation. Data sources: National Vital Statistics Reports and U.S. Department of Agriculture What is the trend? What is the interpretation? 80.57% correlation Does this data PROVE your interpretation is correct? No, but it supports that interpretation. Data sources: National Spelling Bee and Centers for Disease Control & Prevention What is the trend? What is the interpretation? 94.71% correlation Data sources: U.S. Department of Agriculture and Centers for Disease Control & Prevention What is the trend? What is the interpretation? 87.01% correlation Data sources: Wikipedia and Centers for Disease Control & Prevention Hypotheses can be proven to be incorrect, but they generally can’t be proven to be correct. This is why we say the data supports our hypothesis. We don’t say the data proves our hypothesis is correct. The reason why we can’t say definitively that the hypothesis is correct is We can only control for the variables we (1) are aware of, and (2) have the technology to control for. Sometimes our data shows correlation, but it’s much harder to prove causation. Quotes from textbook One can always devise additional hypotheses to explain a set of observations. » For instance another hypothesis to explain our nonworking desk lamp is that the wall socket is faulty You can never test all possible hypotheses …testing supports that hypothesis not by proving it is correct, but rather by failing to prove it incorrect. Although a hypothesis can never be proved beyond all doubt, testing it in various ways can significantly increase our confidence in its validity  Chapter 2 The Chemical Context of Life Elements & Compounds Matter is anything that takes up space and has mass Element: a substance that cannot be broken down to other substances by chemical reactions Molecule: two or more atoms held together by bonds Compound: a substance consisting of two or more elements in a fixed ratio – A compound has characteristics different from those of its elements Emergent properties of a compound Na Cl NaCl Sodium Chlorine Sodium chloride Elements & Compounds There are 92 natural elements. Essential elements are the elements an organism needs to live a healthy life and reproduce – Different species may require different elements – Plants have 17 essential elements Humans have 25 essential elements Chapter 2 Elements Compounds Elements Each element consists of a certain type of atom that is different from the atoms of any other element An atom is the smallest unit of matter that still retains the properties of an element Atoms are composed of subatomic particles STOP & THINK Where have we heard the term “nucleus” Relevant subatomic particles include: before? Neutrons (no electrical charge) Protons (positive charge) Electrons (negative charge)  Atoms are composed of subatomic particles Neutrons and protons form the atomic nucleus Electrons form a “cloud” of negative charge around the nucleus Neutron mass and proton mass are Electrons are so almost identical and small, their mass is are measured in ignored. daltons or atomic mass units (amu) Atomic Number and Atomic Mass STOP & THINK An element’s atomic number is the Do all atoms of Helium have number of protons in its nucleus the same number of protons? An element’s mass number is the sum of protons plus neutrons in the nucleus Atomic mass, the atom’s total mass, can be approximated by the mass number Do all atoms of Helium have the same number of neutrons? © 2017 Pearson Education, Inc. All atoms of an element have the same number of protons Some atoms can have more or less neutrons than other atoms of the same element. These different atomic forms of the same element are called isotopes Example: Carbon-12 and Carbon-13 are isotopes of Carbon The number refers to the atomic mass of that element. How many neutrons does C-12 have? 6 How many neutrons does C-13 have? C Which do you think is more abundant? Carbon 12.011 Radioactive isotopes are unstable isotopes. Example: There is also a Carbon-14 isotope. This is the most rare isotope of Carbon because it is less stable than Carbon-12 and Carbon-13. Radioactive decay: radioactive isotopes tend to “decay” or lose subatomic particles Example: When Carbon-14 decays, a neutron decays into a proton. How many protons does it have now How many neutrons? What does Carbon-14 decay into? Radioactive Tracers can be used in Diagnostics Radioactive atoms can be taken up by the body and used in the same way as they use non-radioactive isotopes of the same atom Radioactive isotopes are often used as diagnostic tools in medicine Cells use radioactive tracers just like non-radioactive atoms Radioactive tracers can be used to track atoms through metabolism © 2017 Pearson Education, Inc. Radiometric Dating A “parent” isotope decays into its “daughter” isotope at a fixed rate, expressed as the half-life In radiometric dating, scientists measure the ratio of different isotopes and calculate how many half-lives have passed since the fossil or rock was formed Each radioactive isotope can have a different Half- life. Half-life values vary from seconds or days to billions of years. » Half-life of Carbon-14 is 5,730 years. From this picture, can you determine » Half-life of Uranium-238 the half-life of Carbon-14? is 4.5 billion years. © 2017 Pearson Education, Inc. What are the 3 main subatomic particles? Protons Neutrons Of these 3 subatomic particles, Electrons these are the ones that are involved in chemical reactions!  Electrons An atom’s electrons vary in the amount of energy they posses Energy is the capacity to cause change, like doing work Potential energy is the energy that matter has because of its location or structure If I carry a rock up a mountain, does that rock have energy? How do I know the rock has energy?  Electrons An electron’s state of potential energy is called its energy level, or electron shell In different electron shells (or locations), electrons have different amounts of potential energy © 2017 Pearson Education, Inc. Electrons Valence electrons are those in the outermost shell, or valence shell The chemical behavior of an atom is mostly determined by the valence electrons Elements with a full valence shell are chemically inert Elements with incomplete valence shells are chemically reactive © 2017 Pearson Education, Inc.  Hydrogen 2 Atomic number Helium 1H He 2He Atomic mass 4.003 Element symbol First shell Electron distribution diagram Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon 3Li 4Be 5B 6C 7N 8O 9F 10Ne Second shell Sodium Magnesium Aluminum Silicon Phosphorus Sulfur Chlorine Argon 11Na 12Mg 13AI 14SI 15P 16S 17CI 18Ar Third shell Which elements have full valence shells? End for today. We will finish Chapter 2 tomorrow. Remember to have appropriate attire before coming to lab! Expect a quiz tomorrow on what we covered today