NU CHEM 1211 - Composition of Earth and Types of Compounds

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Announcements:Homework Assignment #1 is due this Sunday (9/19).Some hardware upgrades at SmartWork last Friday did not go well, and the site was not responding this weekend like it should. The problem should be fixed by this afternoon.Recitations and labs start this weekLast time:II. Measurements in ChemistryThis time:Composition of Earth and Types of Compounds (Sections 2.1, 2.2, 2.7 and 2.8):Prof Gilbert LECTURE 3 CHEM 1211 Fall ‘10Announcements:• Homework Assignment #1 is due this Sunday (9/19).• Some hardware upgrades at SmartWork last Friday did not go well, and the site was not responding this weekend like it should. The problem should be fixed by this afternoon. • Recitations and labs start this weekLast time:I. Chemistry: the science of matterA. Transitions between statesB. Separating mixtures based on differences in physical properties II. Measurements in Chemistry Precision (repeatability of a measurement) vs. accuracy (how close the result is to the true value). Express the uncertainty in measurements using significant figures Follow the weak link rule: we can know the result of a calculation only as well as we know the least well-known value used in the calculation. Adding or subtracting values can result in increasing or decreasing the number of sig fig’s.This time:III. Dimensional Analysis: the key is to make sure that units in the conversion factors are arranged so that the original units cancel out and the desired ones remain. Thus, an original unit in a numerator should appear in the denominator of one of the conversion factors, and vice versa.Composition of Earth and Types of Compounds (Sections 2.1, 2.2, 2.7 and 2.8):Why do we live on a planet with a surface of solid Al, Si and O and a molten core of Fe while the outer planets are gigantic balls of gas?Answer is linked to cosmological distillation: volatile substances condensed farthest from the sun, forming the “gas giants” (Jupiter, Saturn, Neptune and Uranus) the least volatile formed the solid planets closest to it (Mercury, Venus, Earth and Mars). But oxygen is a volatile gas. Why is it so abundant on Earth?The answer lies in the physical properties of the compounds it forms, and particularly their high melting points.Consider the binary (2-element) compounds that O forms. The ones it forms with other nonmetals (blue elements in the periodic table below) are volatile molecular compounds. Examples: CO2 and H2O. These a molecular formulas that indicate the type and number of atoms of each elements in one molecule of the compound. The atoms are held together by shared pairs of electrons called covalent bonds. O forms nonvolatile (solid at room temp.) compounds withgreen metalloids in which the elements are held together byextended 3-D networks of covalent bonds. Ex.: SiO2:O forms compounds with metallic elements (shown in tan) thatare solid ionic compounds. The metals form + cations and Oand the other nonmetals form – anions. Examples: Fe2O3 andNiO. These formulas are called empirical formulas. Theyrepresent the simplest ratio of the ions in the compounds.Formulas and Nomenclature of Compounds Naming binary molecular compounds: name element tothe left and/or below the other in the periodic tablegoes first, ending on the second element is ...ide. Use prefixes to indicate number of atoms of eachelement per molecule because elements can combine in different proportions, such as SO2 and SO3. Examples of Dalton’s law of multiple proportions.Predicting chemical formulas Key concepts: (1) The charges on the common ions can be predicted based on the location of the elements in the periodic table; (2) the (+) and (-) charges have to cancel out.ex. KBr; CaCl2, AlCl3, Na2S, Al2O3, Ca2CNaming binary ionic compounds: simple system - left side element first, right side elements second, name ending in ...ideTransition metal cations: most of them form ions with several charges, so need to specify the charge using Roman numerals, or the older ..ic or ..ous endings: Fe(II) or ferrous; Fe(III) or ferric. Polyatomic ions: Their atoms are held together by covalent bonds but have an overall electrical charge. Polyatomic cations have fewer electrons, and polyatomic anions have more electrons than the sum of those their atoms had initiallyExamples: carbonate (CO32–), sulfate (SO42–), nitrate (NO3–), phosphate (PO43–) (oxoanions), hydroxide (OH–), and ammonium (NH4+).Naming them: the ending depends on the number of oxygen atoms bonded to the central atom. Large number = high oxidation state of central atom, and the ending is ..ate; lower number, ending is..ite.For example: NO3– is nitrate, and NO2– is nitriteUse hypo (as in hypothermia) or per prefixes to indicate very low or high #s of O atoms, as in the oxoanions of the Group 7A elementsOxoacids: when the cation is H+: ..ate oxoanion turns into ..ic acid and ..ite oxoanion turns into ..ous acid. Examples: NO3– (nitrate) + H+ → HNO3 (nitric acid) NO2– (nitrite) + H+ → HNO2 (nitrous acid)______________________Binary acids: hydro____ acid. Ex: Name of aqueous HCl is hydrochloric


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NU CHEM 1211 - Composition of Earth and Types of Compounds

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