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CHEM 1061
Hyunjoo Im

Background Unit Notes 1.3 Scientific Measurements  Système international d'unités (International System of Units) (SI) o Length: meters (m) (1/10,000,000 distance from equator to North Pole along meridian) o Area and Volume: Liter (L) (1L = 1dm ; 1mL = 1cm ) 3 o Mass: quantity of matter in an object (same anywhere); kilogram (kg) o Weight: force of Earth’s gravity on the object (different at different places) o Time: seconds (s) (smaller uses prefixes, longer uses minutes (min), hour (h), day (d), year (y)) o Temperature: measure of energy or what direction heat flows; Kelvin (K)  Celsius (ºC): boiling point: 100 ºC, freezing point: 0 ºC  Fahrenheit (ºF): boiling point: 212 ºC, freezing point: 32 ºC  TF= 1.8T +C32; T = CT – 32F/1.8 o Electric Current: Ampere (A) o Amount of substance: Mole (mol) o Luminous intensity: Candela (cd)  Prefixes 12 o Tera (T) = 10 o Giga (G) = 10 9 6 o Mega (M) = 10 o Kilo (k) = 10 3 2 o Hecto (h) = 10 o Deca (da or dk) = 10 1 -1 o Deci (d) = 10 o Centi (c) = 10 -2 -3 o Milli (m) = 10 o Micro (µ) = 10 -6 -9 o Nano (n) = 10 o Pico (p) = 10 -12 1.4 Precision and Accuracy in Measurements  Precision: how closely individual measurements agree w/ one another  Accuracy: how close average of the set comes to the true/most probable value  Need representative samples, which tell what conditions were present for what trials when experimenting  Significant figures: all digits known with certainty & the first uncertain digit o More significant figures more precise the measurement o All nonzero digits = significant o Zero btwn sig figs & to rights of decimal pt (if @ end of #) = sifnificant. o Zero before decimal pt is not significant; zeros on right of decimal pt before 1 st nonzero digit are not significant; zero @ end of # w/o decimal point aren’t significant o EXCEPTIONS: 1) counting #, inherently an integer 2) fraction 3) defined quantities/ conversion factors…. All = exact values, don’t count sig figs o Multiplying/dividing: ans has as many sig figs as given # w/ least sig figs o Addition/subtraction: ans has # of digits to right of decimal pt as given # w/ least digits to right of decimal pt o Rounding: 0,1,2,3,4 unchanged; 5,6,7,8,9  increase o Follow order of operations when determining sig figs at end. 1.5) A Problem Solving Method  Conversion factor: ratio of diff units of measurement equivalent to # 1.  Dimensional Analysis: multiply given by conversion factors; same units are diagonal, so they cancel out -3  Density: mass per volume of a substance; d = m/V; kgm  *immiscible: substances don’t mix to form solution liquid w/lower density on top of higher density o Floating solid displaces mass of liquid o Sinking solid displaces volume of liquid 1.6) Further Remarks on Problem Solving  Quantitative: can be described/answered w/ numbers  Qualitative: described/answered with statement, picture, symbols, diagram, yes/no, etc.  Estimation: see if ans = reasonable 1.2) Getting Started: Some Key Terms  Chemistry: study of composition, structure, & properties of matter & of changes that occur in matter  Matter: anything that has mass & occupies space *heat & light aren’t matter, they’re forms of energy  Macroscopic level: can be seen w/ naked eye  Microscopic level: need special instruments to see small particles  Atoms: smallest distinctive units in a sample of matter  Molecules: larger 2 or more atoms joined together  Composition: types of atoms & relative proportions of different atoms in a sample of matter Properties  Physical Property: a characteristic displayed by a sample of matter without undergoing any change in its composition o Color o Odor o Electric conductivity o Brilliance and hardness  Chemical Property: a characteristic displayed by a sample of matter that undergoes a change in composition o Flammability  Physical change: matter undergoes noticeable change at the macroscopic level, but no change in composition o Changing state of matter  Chemical Change/ chemical reaction: matter undergoes change in composition/structure of molecules o Flame Classifying Matter (substance or mixture)  Substance: type of matter that has definite, fixed composition that doesn’t vary from one sample of substance to another; all substances = element or compound o Element: substance that can’t be broken down into other simpler substances by chem reaction; made of single type of atom o Compound: substance made of atoms of 2+ elements w/ diff kinds of atoms combined in fixed proportions; can be broken down into elements by chem reaction o Chemical Symbol: one or 2 letter designation derived from name of element st nd (English or Latin); 1 letter capitalized, 2 lower case; chemical formulas: combinations of chemical symbols  Mixture: no fixed composition o Homogeneous mixture: (solution) has same composition & properties throughout o Heterogeneous mixture: varies in composition and/or properties from one part of mixture to another o Can be separated into individual components by physical changes; chem reactions not required Scientific Methods  Scientific knowledge = testable, reproducible, explanatory, predictive, and tentative  Observations  hypothesis: tentative explanation/prediction concerning some phenomenon  Experiment: test hypothesis through carefully controlled procedure  Data: facts obtained through careful observations/measurements in experiments; = reproducible  Scientific laws: summary of patterns in large collections of data; may use models\  Theory: explanations of observed natural phenomena & predictions that can be tested by further experiment  Scientific knowledge ≠ absolute; never completely true, can be disproved 11.1) Intermolecular Forces and the States of Matter  Intramolecular forces = w/in a molecule; determine molecular geometry, dipole movement  Intermolecular forces (IMFs) = btwn many molecules; determines macroscopic physical properties of liquids and solids; related to chem bonds in substances  States of matter o Gas: expands to fill its container, no fixed volume (vol), no fixed shape, easily compressed  Speedy, energetic, widely spaced atoms/molecules undergo frequent collisions, but never come to rest/clump together o Liquid: fixed volume, no fixed shape, flows to cover bottom & assumes shape of portion of container it fills; only slightly compressible  Atoms/molecules = close together, IMFs = strong enough to hold them in fixed vol, but not definite shape o Solid: fixed volume, fixed definite shape, more difficult to compress than liquid  Structural particles (atoms, ions, molecules) = in direct contact w/ one another, strong IMFs fixed vol, definite shape o In any state of matter, atoms/ions/molecules move: liquid & gas: 3D
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