Scientific Method



AP Bio --- Week 1 NotesScientific Method Observe Ask a question Hypothesis Test Collect and analyze dataDraw conclusion Communicate Independent variable: The item being tested in the experiment. It is intentionally changed by the experimenterDependent variables: The item being measured in the experiment. It is directly affected by the independent variableConstant variables: One or more factors associated with the experiment that do not change or are not allowed to vary throughout the procedureControl Group: The part of the experiment that is used as a comparison for the independent variable; it is unchanged from its normal circumstancesExample Independent variable = different types of plants Dependent variable = oxygen outputConstant variable = size of pot, type of soil, amount of water, amount of sunlight, temperature, etc.Control Group = one group for which you already know the outcome. Group with known dependent variable (given these same conditions)Chemistry – atoms and bondsLiving an non-living matter is composed of atoms Dalton: mass of one proton or neutron1.7 x 10-24 gramsElement: pure substance that contains only one kind of atomAtom: Smallest unit of matter that still retains property of an elementLiving things are mostly composed of 6 elements:Carbon Hydrogen Nitrogen Oxygen Sulfur Phosphorous The number of protons identifies an element= atomic number For electrical neutrality the number of protons = number of electronsMass # = total number of protons + neutrons Bohr model for atomic structure: large empty space and electrons occur in orbits and electron shellsBehavior of electrons determines whether a chemical bond will form and what shape the chemical bind will have Molecule: when atoms bond together Compound: when elements bond together All compounds are molecules but not all molecules are compoundsBondsAtoms with unfilled shells undergo reactions to fill their outer shellsCan attain stability by sharing/losing/gaining electronsChemical bond is an attractive force that links atoms together to form molecules IONIC BONDS Metal + non-metalResult from the electrical attention btwn ions with opposite charges Resulting molecules are called salts Ions are charged particles that form when an atom gains/loses 1 or more electrons Cations: positively charged ionsAnions: negatively charged ions Ionic attractions are weak, that is why salts dissolve so easily in water COVALENT BONDSForm when 2 or more atoms share pairs of electrons The atoms attain stability by having full outer shellsEach atom contributes one member of the electron pair Properties of molecules are influenced by characteristics of the covalent bondsOrientation: length, angle, and direction of bonds btwn any 2 elements are always the sameEx: methane always forms a tetrahedron Strength and Stability: covalent bonds are very strong; it takes a lot of energy to break them Multiple BondsSingle: sharing of 1 pair of electronsC – HDouble: sharing of 2 pairs of electronsC=HDegree of sharing electrons is not always equalElectronegativity: attractive force that an atomic nucleus exerts on electrons Depends on the # of protons and the distance btwn the nucleus and the electronsPolar Covalent Bond: unfair sharing of electrons due to the different electronegativities. Electrons tend to be near the most attractive atom (the more electronegative atom)Non-Polar Covalent Bond: each atom has the same electronegativity. So the electrons are shared equally See “Chapter 2 Powerpoint” in the Honors Biology section of the website for more information ................
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