Chem 127, Book Notes - Week 1
Chem 127, Book Notes - Week 1 CHEM 160
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This 9 page Class Notes was uploaded by Aenea Mead on Sunday September 25, 2016. The Class Notes belongs to CHEM 160 at California Polytechnic State University San Luis Obispo taught by unknown in Fall 2016. Since its upload, it has received 8 views. For similar materials see General Chemistry for Agriculture and Life Science I in Chemistry at California Polytechnic State University San Luis Obispo.
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Date Created: 09/25/16
Chapter 1: Section 45, Chapter 2: Section 3, 45 1.4) Measurement A measurement can tell you three things: 1) Size or magnitude (the number) 2) Something to compare it to (the unit) 3) Degree of certainty (# of sig figs) Unit standards of comparison for measurements SI Unit base units by which most scientific measurements of measured in and from which all other units can be derived Base Units of the SI System Property Measured Name of Unit Symbol of Unit Length* meter m Mass* milogram kg Time* second s Temperature* kelvin K Electric Current ampere A Amount of Substance mole mol Luminosity Intensity candela cd *More commonly used base units Sometimes if a measurement is too big or too small it doesn’t make sense to write it in terms of the base unit so fractionals or multiples of the unit are used by adding a set prefix. A few common prefixes are: Fempto (f) = 10 −15 −12 Pico (p) = 10 Nano (n) = 10 −9 −6 Micro (μ) = 10 −3 Milli (m) = 10 Centi (cm) = 10 −2 Deci (d) = 10 −1 3 Kil0 (k) = 10 Mega (M) = 10 6 9 Giga (G) = 10 Terra (T) = 10 12 **Note: It is not necessary to memorize these, however it will make solving problems easier if you have them on hand so that you do not waste time constantly looking them up. Base units can be mixed to derive other units (similar to how primary colors can be mixed to get secondary colors). Ex. length can be used to derive volume, mass and length can be used to derive density ↓ ↓ ↓ ↓ ↓ Volume the amount of space an object occupies, SI unit is m 3 3 Density the ratio of mass to volume in a sample, SI unit is kg/m 1.5) Sig Figs, Accuracy and Precision Due to practical limitations no measurement done by man is exact. Significant figures (often referred to as “sig figs”) are used to report a measurement as accurately as possible. Sig Fig Rules: 1. All non zero digits are significant. 2. Any zeros sandwiched between two non zero digits are significant 3. Zeros to the right of the decimal are significant 4. Non sandwiched zeros to the left of the decimal are NOT significant (rule does not apply when decimal point is present) Examples: 1. 1389 4 sig figs 2. 56.0 3 sig figs 3. 50. 2 sig figs 4. 50 1 sig figs 5. 80.809 5 sig figs 6. 5001 4 sig figs 7. 0.00393820 6 sig figs Knowing how to determine sig figs is important for knowing how to write an answer for a calculation. It would not be accurate to declare the number of molecules in your samples to be 8.83902849 x 10^22 just because your calculator spit it out. In reality you only really know a few of those digits to be accurate, and the rest should be discarded. Sig Figs in Calculations: When using a measured number to make a calculation it is important to keep in mind that the calculated number cannot be more exact than the numbers being calculated. It is important to record a measured amount as accurately as possible with the least degree of uncertainty. Some rules to go by: 1. When adding or subtracting the result should be rounded to the same number of decimal places as the number with the least number of decimal places. Ex. 154+23.44=177.44 → 177 2. When multiplying or dividing the answer should be rounded to the number of digits as the number being multiplied/divided with the least number of sig figs. 2.5) The Periodic Table The periodic table is organized into 18 columns, call groups, and 7 rows, called series or periods. The elements in the periodic table are organized due to their various properties (such as valence shell, metals/nonmetals/metalloids, etc) NOT simply by increasing number of protons. Basic organization of the periodic table ↓ More detailed version of the organization ↓ 2.6) Bonding Basics As mentioned in section 2.3, an atom can gain or lose electrons, thus making it an ion. The periodic table can be used to predict whether an atom will gain or lose electrons. For instance alkali and alkaline earth metals will lose one or two electrons to match the number of electrons as the previous noble gas. 2+ Ex. Be w ill lose two electrons to become Be On the other side of the table the nonmetals will gain one to three electrons to match the number of electrons at the next noble gas. Ex. Cl gains one electron to become Cl +