Week 3 Notes, Chapter 2-Chapter 3
Week 3 Notes, Chapter 2-Chapter 3 CHM 113
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Date Created: 09/01/16
Chapter 2 8-29 & 8-31 Monday, August 29, 2016 3:01 PM SI Sessions Monday 7:00pm-7:50pmin Pablo 101 Wednesday 6:00-6:50WXLR A118 Fridays 10:00AM-10:50in MSHAL F-101 Read pg. Chapter 2: 40-73 Chapter 4: 140-141 Chapter 8: 301-309 Notes from readings: Chapter 2- Greek Philosophers described the material worlds as made up of tiny, indivisible particles they called atomos meaning indivisible or uncuttable. The law of constant composition: In a given compound, the relative numbers and kinds of atoms are constant. The law of conservation of mass: The total mass of materials present after a chemical reaction is the same as the total mass present before the reaction. The law of multiple proportions: If two elementsA and B combine to form morethan one compound, the masses of B that can combine with a given mass of A are in the ratio of small whole numbers. Thomsonusing his cathode experimentdetermined the charge to mass of an electron was 1.76 X 10 coulombs per gram. Once the charge -to- mass ratio was determined,in 1909 Robert Millikan of the University of Chicago measured the charge of an electron using his oil-drop experiment which resulted in a calculation of 1.602X 10 -1C. He then calculated the mass of an electron to be 9.10 X 10 g8 Radioactivity-The spontaneous emission of radiation Three types of radiation: alpha ( α), beta (β ) and gamma ( γ). Alpha and beta waves are affected by electrical fields but in opposite ways. Gamma radiation isn't affected. Alpha waves are positively charged, beta waves are negatively charged and gamma waves carry no charge. Nuclear Model of the Atom Thomson's plum-pudding model explained the atom as filled with electrons, which was short lived. Rutherford's gold-foil experiment later disproved this model as some particles became scattered when they hit the gold foil. This proved that most of an atom was empty space. 2.3 The Modern View of Atomic Particles The charge of an electron is -1.602*10 C.Protons are oppositely charged in sign but the same in -19 magnitude; +1.602*10 C.Neutrons carry no charge. Every atom has an equal number of protons and electrons, so atoms have no net electrical charge. Most atoms have diameterswithin 100 and 500 picometers.For example, a chlorine atom has a diameter of 200 pm. Since atoms have extremely small masses, we use the atomic mass unit (amu) where 1 amu = 1.66054 X 10 -24g. A proton has a mass of 1.0073amu, a neutron 1.0087 amu and an electron of -4 5.486 X 10 amu. Most of the mass of an atom is contained in the nucleus. CHM 113 Lecture Page 1 Basic Forces Four basic forces are known: gravitational, electromagnetic,strong nuclear and weak nuclear. The magnitude of the electric force between two charged particles is given by Coulomb's Law: F=kQ 1 /2 ,where Q1 and Q2 are the magnitudes of the charges on the two particles, d is the distance between their centers and k is a constant determinedby the units for Q and d. Atomic numbers, mass numbers and isotopes The number of protons in an atom of any particular elementis called that element's atomic number. The atomic number is indicated by the subscript; the superscript called the mass number, is the number of protons plus neutrons in the atom: Atoms with identical atomic numbers but different mass numbers are called isotopes. 2.4 Atomic Weights It is convenient to use the atomic mass unit when dealing with these extremely small masses: 1 amu=1.66054X 10 g and 1 g= 6.03314X 10 amu 23 The atomic mass unit is presently defined by assigning a mass of exactly 12 amu to a chemically unbound atom of C isotope of Carbon. Atomic weight = [(Isotope mass) X (fractional isotope abundance)] All isotopes of the element Atomic weight of chlorine= (.7578)(34.969amu) + (.2422)(36.966amu) =26.50 amu + 8.953 amu =35.45 amu 2.5 The Periodic Table Elements are in order of increasing atomic number. Horizontal rows are called periods. Vertical columns are groups. Elements in the same group have similar properties. Group 1A Alkali metals Li,Na,K,Rb,Cs,Fr 2A Alkali earth metals Be, Mg, Ca, Sr, Ba, Ra 6A Chalcogens O, S, Se, Te, Po 7A Halogens F, Cl, Br, I, At 8A Noble gases (or rare gases) He,Ne,Ar,Kr,Xe,Rn All elementson the left and middle of the table are metallic elements or metals. (Except hydrogen) CHM 113 Lecture Page 2 hydrogen) Metals share properties such as luster, high electrical and heat conductivity and all metals except mercury (Hg) are solid at room temp Nonmetallic elements or nonmetals runs from boron to astatine. At room temp some are gaseous, some are solid and one is liquid. Many elements that fall near the line of metals and nonmetals have properties of both and are named metalloids. 2.6 Molecules and Molecular Compounds A moleculemade up of two different atoms is called a diatomic molecule. Compounds composedof molecules containmore than one type of atom and are called molecular compounds. CH for4example. Chemical formulas that indicate the actual numbers of atoms in a molecule are called molecular formulas. Chemical formulas that give only the relative number of atomsof each type in a moleculeare called empiricalformulas. H O -> HO 2 2 Ball and stick models show atoms as spheres and bonds as sticks. This accurately represents the angles at which some atoms are attached. A space fillingmodel depicts what a moleculewould look like if the atoms were scaled up in size. 2.7 Ions and Ionic Compounds If electrons are removedor added to an atom, a charged particle called an ion is formed. An ion with a positive charge is a cation; a negatively charged ion is an anion. + Polyatomic ions such as NH co4sist of atoms joined together but carry a net positiveor net negative charge. Sodium chloride, aka table salt, is an example of an ionic compound, made up of cations and anions. Ionic compounds are generally combos of metals and nonmetals. Molecular compounds are generally composed of nonmetals only as in H O.2 - + If charges on both cation and anion are equal, the subscript of each ion is 1. Cl + Na = NaCl If charges aren't equal, the charge on one ion will becomethe subscript of the other. Mg + N = Mg N 3 2 2.8 Naming Inorganic Compounds Organic compounds contain carbon and hydrogen, often in combination with oxygen, nitrogen and other elements. Inorganic compounds are all other types of compounds. There are three types: ionic compounds, molecular compounds and acids. If metals form more than one cation, use a romannumeral to indicate the charge. Cations formed from nonmetal atoms have names that end in -ium. Anions The names of monatomic anions are formed by replacing the end of the name of the element with - ide: - 2- 3- H Hydride ion O oxide ion N nitride ion CHM 113 Lecture Page 3 A few polyatomicanions also have names ending with -ide: - - 2- OH hydroxide ion CN cyanide ion O 2 peroxide ion Polyatomic ions containing oxygen have names ending in either -ate or ite and are called oxyanions. -ate is the most commonrepresentative oxyanion of an element. -ite is for an oxyanion with one O atom fewer - 2- NO 3 Nitrate ion SO 4 Sulfate ion NO - Nitrite ion SO 2- Sulfite ion 2 3 Prefixes are used when the series of oxyanionsof an element extends to four members, as with the halogens. The prefix per- indicates one moreO atom than the oxyanionending in -ate; hypo- indicates one O atom fewer than the oxyanion ending in -ite. Ionic Compounds Names of ionic compounds consist of the cation name followed by the anion name. Names and Formulas of Acids Acids containing anions whose names end in -ide are named by changing the -ide to -ic adding the prefix hydro- to this anion name , and then following with the word acid. HCl- hydrochloric acid Acids containing anions whose names end in-ate or -ite are named by changing -ate to -ic and -ite to -ous and then adding the word acid. Perchlorate Perchloric acid Chlorate Chloric acid Chlorite Chlorous acid Hypochlorite Hypochlorousacid Names and Formulas Binary Molecular Compounds The procedure used for naming binary (two-element)molecular compounds are similar to naming ionic compounds 1. The name of the element farther left is written first, (unless the compound contains oxygen and chlorine, bromine or iodine [any element except fluorine]) 2. If both are in the same group the one closer to the bottom is named first. 3. The name of the second elementis given an-ide ending 4. Greek prefixes indicate the number of atoms in each element. (di-,tri-….) 2.9 Some Simple Organic Compounds The study of compounds of carbon is called organic chemistry Compounds that only contain carbon and hydrogen are called hydrocarbons, the simplest class being alkanes. Methane Ethane Propane The alkane with four carbons is butane. For five or more carbons, refer to the prefixes from table 2.6. (penta-,hexa-..) Some derivativesof alkanes Other classes of organic compounds are obtained when one or more hydrogen atoms in an alkane are replaced with functional groups. An alcohol for example is obtained by replacing an H atom of an alkane with an -OH group. The name of the alcohol is derived from that of the alkane by adding an -ol ending. CHM 113 Lecture Page 4 An alcohol for example is obtained by replacing an H atom of an alkane with an -OH group. The name of the alcohol is derived from that of the alkane by adding an -ol ending. Methanol Ethanol 1-Propanol Methane, ethane and propane are all colorlessgases while methanol,ethanol and propanol are all colorlessliquids. The prefix "1" in the name 1-propanol indicates that the replacement of H with OH has occurred at one of the "outer" carbon atoms. 2-propanol or isopropyl alcohol is obtained when OH is attached to the middle carbon. Compounds that have the same molecularformula but different arrangements of atoms are called isomers. For example:2-bromobutane,butyric acid and butyl methyl ether Notes from lecture- 2.1 The Atomic Theory of Matter There are approximately100 distinct elements. Each is composedof unique atoms. The theory that atoms are the fundamental building blocks of matter reemerged in the 19th century, from John Dalton. Subatomic Particles Electron Proton Neutron 1897 (Thomson):Electron discovered using a cathode-raytube. Detectionof negatively charged particle. (-1) Thomsonmade a model for the atom later called the "plum pudding model" Rutherford discovered protons in 1919 Neutrons were discovered by James Chadwick in 1932 Amu= exactly 1/12 the mass of a carbon atom. CHM 113 Lecture Page 5
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