Prof Gilbert LECTURE 3 CHEM 1211 Fall 10 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 week Last time I Chemistry the science of matter A Transitions between states B 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 with green metalloids in which the elements are held together by extended 3 D networks of covalent bonds Ex SiO2 O forms compounds with metallic elements shown in tan that are solid ionic compounds The metals form cations and O and the other nonmetals form anions Examples Fe2O3 and NiO These formulas are called empirical formulas They represent the simplest ratio of the ions in the compounds Formulas and Nomenclature of Compounds Naming binary molecular compounds name element to the left and or below the other in the periodic table goes first ending on the second element is ide Use prefixes to indicate number of atoms of each element 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 Naming binary ionic compounds simple system left side element first right side elements second ex KBr CaCl2 AlCl3 Na2S Al2O3 Ca2C name ending in ide Transition 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 initially Examples carbonate CO3 and ammonium NH4 2 sulfate SO4 2 nitrate NO3 phosphate PO4 3 oxoanions hydroxide OH 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 nitrite Use 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 elements Oxoacids 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 acid