Popular in Chemistry 1
Popular in Chemistry
This 4 page Class Notes was uploaded by Stephanie Belo on Thursday January 14, 2016. The Class Notes belongs to CHM2045 at a university taught by John Mitchell in Spring 2016. Since its upload, it has received 20 views.
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Date Created: 01/14/16
CHM 2045: Chapter 1 & 2 1/8/16 Chapter 1 • Physical property – A characteristic shown by a substance itself, without interacting with or changing into other substances. • Chemical property – A characteristic of a substance that appears as it interacts with, or transforms into, other substances. • Homogeneous Mixture • Homogeneous mixtures have only one phase, or have a uniform appearance throughout, and any portion of the sample has the same properties and composition. • Heterogeneous Mixture • A heterogeneous mixture is made of different substances that remain physically separate. • Allotrope: one of two or more existing forms of an element o Ex. Diamond & graphite • Dimensional analysis problem solving-‐ use conversion factors o Ex. If the avg. distance from the sun to the earth is 96 million miles. With light traveling at 2.99 * 10^8 m/s how many minutes does it take for light to travel from the sun to the earth? (1 km = 0.6215 mile, or 1 mi = 1.609 km) o 96 * 10^6 miles * 1.6093 km/1 mile * 1000m/1km * 1s/2.99*10^8 m * 1 min/60 s = 8.610 min à 8.6 min (use 2 significant figures—go with the least amount of sig figs in the given problem) Significant Figures Rules 1. All numbers other than zero are significant (ex. 243 has 3 sig figs) 2. Leading zeros: a) Zeros in front don’t count (ex. 0.00007 only has 1 sig fig) b) Zeros that are at the end of a number and also to the right of the decimal are significant. c) Zeros between other significant digits are significant. (ex. 2004 has 4 sig figs) d) Zeros at the end of a number are not significant if there’s no decimal in the number. (ex. 2000 just has 1 sig fig) Last point: counting numbers and conversions have an infinite number of sig figs Addition and Subtraction Significant Figures Rules The answer has the number decimal places equal to the number w the fewest digits after the decimal. Ex. 0.12 + 1.9 + 10.925 = 12.945 à Answer: 12.9 (only 1 decimal place b/c of 1.9) Multiplication and Division Sig Fig Rules The answer has the number of sig. figs. Equal to the number w the fewest sig figs. Ex. 0.01208/0.236 = 0.512 *Know SI prefixes (giga, nano, pico, deca, etc.) Chapter 2 Atomic Structure: Know: avg. atomic weight, how to read periodic table (Groups, families, metals, nonmetals, metalloids), the 7 diatomics MUST KNOW: H , N , O , F , Cl , Br , I 2 2 2 2 2 2 2 –Have No Fear of Ice Cold Beer Atomic Structure • Atoms have no net charge o Ions (Na , Cl ) must be declared Atomic Composition A Z – the symbol of the atom or isotope X = Atomic symbol of the element A = mass number (A = Z + N – protons plus neutrons) Z = atomic number (# of protons in the nucleus N = # of neutrons in the nucleus 2 Atomic Number (Z) and Mass (A) • We can only get the relative mass of an atom, that is relative to one another • Example of relative: The mass of an oxygen atom is 1.333 times more massive than an atom of Carbon. • We base everything against C-‐12 (Carbon w 6 protons and 6 neutrons) in chemistry just like we base weight in the US against the pound. • The decimal number is the Atomic mass o The Atomic Mass and is equal to the mass, in atomic mass units (amu) (1/12 of a C-‐12 atom) of the element. Isotopes • Isotopes have the same number of protons but different number of neutrons • Bc of the existence of isotopes, the mass of a collection of atoms has an average value • Average mass = ATOMIC WEIGHT • Boron is 19.9% B-‐10 and 80.1% B-‐11. That is, B-‐11 is 80.1 percent abundant on earth. o (0.199 * 10.0 amu) + (0.801 * 11 amu) = 10.8 (ßfrom periodic table!) • Exam Isotope question o Boron has 2 stable isotopes w masses of 10.00 amu and 11.00 amu. What is the percent abundance of each isotope? (Note: simple low sig. fig. numbers used in this example. Exam questions will have 6 sig figs in the masses.) o (x * 10 amu) + (y * 11.0 amu) = 10.8 Total % = 100% = 1 x + y = 1 x = 1 – y ((1-‐y) * 10) + (y * 11) = 10.8 3 y = 1 – x (when solving for x use this) Nomenclature • If it’s in the textbook you are responsible for the nomenclature • NaCl, salt = ionic compound (atoms all jammed together, little space between them) • Ethanol, C H O 2 =6 molecular compound (atoms more spread out) Condensed formula-‐ groups atoms next to where they are bound (ex. CH OH) 3 Empirical formula-‐ a formula giving the proportions of the elements present in a compound but not the actual numbers or arrangement of atoms Know Methane, ethane…..decane Ionic Compound, Formulas, Names, and Properties • If first element in a compound is a metal, then the compound is ionic • Na SO (2odium4 ulfate) would be ionic • PCl = molecules bc phosphorus is not a metal 5 Al2(SO4)3 = aluminum sulfate –NOT aluminum (III) sulfate (it’s an “always”) 4
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