Chapter 2 Atoms and Molecules.docx

7 Pages
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Department
Chemistry and Biochemistry
Course Code
CHEM 6A
Professor
Bill Trogler

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1. Definitions – The language of chemistry a. Matter – Anything that has mass and volume – chemical compounds, planets, trees, people b. Composition – The types and amounts of simpler substances (atoms – elements) that make up a sample of matter c. Properties – the characteristics that give each substance a unique identity i. Physical Changes: 1. Chemical bonds remain intact 2. boil, evaporate, sublimation ii. Gases are compressible fluids. Widely separated iii. Liquids are relatively incompressible fluids iv. Solids are nearly incompressible and rigid; molecules or ions are in close contact/immobile, and the only movement is vibration. d. Element – consists of only one type of atom, and cannot be broken down into simpler substances by physical or chemical means. Simplest type of substance with unique physical and chemical properties. e. Molecule – Structure consists of two or more atoms that are chemically bound together, behaves as independent unit. f. Compound – Substance composed of two or more elements which are chemically combined. 2. Periodic Table a. Since many metals exhibit similar types of reactions, it is a property a chemist immediately thinks about when he or she encounters the symbol for the element. b. Metalloids divide metallic elements on left from nonmetals from the right (except hydrogen) Therefore memorize the metalloids, so you can classify the metals as those to the left of the metalloids, and the nonmetals as those to the right (except for hydrogen) 3. Mixtures a. Group of two or more substances that are physically intermingled (mud, skim milk, etc..) i. Asolution is a special type of homogenous mixture, such as sea water, brass, where everything is in the same phase. Solutions in water solvent are very common and called aqueous solutions. 1. Solvent is the term for the majority liquid component and solute is used for the minor component that is dissolved. ii. Heterogeneous Mixtures have one or more visible boundaries iii. Homogeneous Mixtures or Solutions have no visible boundaries because the components are mixed as individual atoms, ions, and molecules, such as aqueous solutions. May exist in all three physical states. b. Elements that are diatomic in their natural state: i. Hydrogen ii. Oxygen iii. Nitrogen iv. Flourine v. Chlorine vi. Bromine vii. Iodine 4. Law of Mass Conservation a. Total mass of substances does not change during a chemical reaction. 5. Law of Definite (Constant) Composition a. No matter the source, a particular pure compound is composed of the same elements in the same parts (fractions) by mass. 6. Calculating the Mass of an Element in a Compound a. Problem: Quartz or silica is the principal component in sand and has the formula SiO2.Analysis shows that 60.08g of quartz contains 28.05 g of the element silicon, with oxygen as the only other element. How many grams of silicon, which is used to make computer chips, can be obtained from 150kg of silica? i. The mass fraction of silicon (Si) in silica Sam Kantonen [email protected] 419-235-6092 Quiz every 2 – 3 Weeks, 4 – 5 questions 4 quizzes, but lowest one dropped Discussion 1 1. a. What is a significant figure? i. Defines how precise a measurement is ii. Non-zero terms are always significant figures: 1. 1.61 = 3 significant figures 2. 1.21 = 3 significant figures 3. 323.4 = 4 significant figures iii. Any “zero” terms between any non-zero terms are significant as well: 1. 34,001 = 5 significant figures iv. “Trailing” zeros are always insignificant figures, unless bounded by decimals or bars (the number in the bar also counts), or are after decimal points. 1. 0.0034 has two significant figures, they simply define the magnitude of the number. 2. 0.00340 has three significant figures, because the trailing zero counts. The number with the fewest significant figures limits the number of significant figures in the answer. v. Rules 1. 1. All non-zero digits are considered significant. a. For example, 234.56 has five significant figures: 2, 3, 4, 5, and 6. 2. Zeros appearing anywhere between two non-zero digits are significant. a. For example, 201.34 has five significant figures: 2, 0, 1, 3, and 4. 3. Leading zeros are not significant. a. For example, 0.00023 has two significant figures: 2 and 3. 4. Trailing zeros in a number showing a decimal point are significant. a. For example, 23.4500 has six significant figures: 2, 3, 4, 5, 0, and 0. 5. If the left-most digit dropped is the number five or greater (5 through 9), round up. vi. Multiplication 1. The number with the fewest significa
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