LBS 171 REVIEW OUTLINE INTRODUCTORY INFORMATION Chemistry the study of matter and its changes Proust s Law of Definite Proportions any sample of a pure compound will have the same elemental composition by mass DALTON Law of Multiple Proportions if elements A and B form two different compounds the ratio of the compounds mass ratios is a whole number or a simple fraction Atomic Theory of Matter Elements are composed of tiny particles called atoms Atoms of the same element have the same mass and the same chemical properties Atoms combine in whole number ratios to form compounds Chemical reactions do not change the atoms only the way they are combined ATOMS Composed of Protons p Neutrons n Electrons e Element defined by number of p z In a neutral atom number of p number of e Mass number A p n Atoms of same element with different A are isotopes Atomic mass units 12 atomic mass units u is the mass of one atom of 12C THE MOLE AND ITS MEASURES 12 1 mole amount of substance that has as many entities as 12 grams of C 23 Avigadro s Number 6 022 10 number of entities in 1 mole 23 6 022 10 u 1 gram Molar mass of an element mass of 1 mole of atoms in grams Molar mass of a compound sum of molar masses of all individual atoms in the compound Molar Mass M o Used to measure moles of a substance in solution o M mol solute L solution In dilutions M1V1 M2V2 MICELLANEOUS MEASURES Density Mass of sample volume of sample Percent yield Experimental mass of product Theoretical mass of product STOICHIOMETRY measuring elements Must use a balanced chemical equation Balancing equations 1 Never change subscripts 2 Use coefficients in front of chemicals to balance atoms that appear only once per side 3 Use coefficients fractions are OK to balance atoms that appear more than once per side 4 Multiply divide to get the smallest whole number ratio Sometimes an excess of one reactant is used o Limiting reactant used up first Reaction stops when limiting reactant in gone o Excess reactant some remains after reaction stops o Hint if you are given a way to find moles of all starting materials it is probably a limiting reactant problem ATOMIC STRUCTURE THE e IS CRITICAL IN CHEMISTRY Sharing of e between atoms chemical bonding Rearrangement of e between atoms chemical reactivity Unpaired e magnetism e travel in a solid conductivity CATHODE RAY EXPERIMENT late 1800 s http www lightandmatter com html bo oks 4em ch01 figs deflect png First evidence of eCathode ray attracted to a electrical field and deflected by a field showed that the particles had a charge ATOMIC MODELS J J Thompson late 1800 s proposed plum pudding model hard e buried in spongy material Rutherford 1911 gold foil experiment http abyss uoregon edu js images rutherford exp gif o particles shot through gold foil in front of phosphorescent screen o Observed one large glowing spot opposite the emitter and several tiny flickering spots all over screen o Shows that the atom is mostly empty space and has small hard charged nucleus RYDBERG Passed current through tube of low density H2 gas Emission spectrum had four distinct colored lines for a reason unknown to him Emperical equation for wavelength of each of the colored lines in H emission spectrum 1 R 1 ni2 1 nf2 where ni 3 4 5 6 nf 2 R 1 097 107 m 1 ELECTROMAGNETIC RADIATION http www hull ac uk chemistry spectroscopy terms wave jpg Frequency number of peaks that pass by a given point in 1 second 1 s Hz Wavelength distance from peak to peak usually in nm c c speed of light 3 00 108 m s Ephoton h h Plank s Constant 6 626 10 34 J s Spectrum http acept la asu edu PiN rdg color spectrum gif o Gamma rays high E very toxic produced by black hole collisions and during radioactive nuclear decay o X rays high E toxic in high doses produced when high E e collide with metal target o UV and visible caused by e dropping to lower E levels o Infrared emitted by vibrating chemical bonds o Microwaves produced by circulating electrical field causes molecular rotation o Radio waves caused by oscillating electrical fields NIEL BOHR Explained why only four lines were observed in H emission spectrum e orbits nucleus in circular path only certain orbits with specific energies are allowed Electrical or thermal E can promote e to higher E orbits Light is emitted when e drop down in orbits E of light emitted corresponds only to the E gaps between the orbits that the e travels 2 Equation for energy of an e in an H atom E Rhc n where n is orbit number principle quantum number as mentioned below 2 2 From above equation E Efinal Einitial Rhc 1 nfinal 1 ninitial Energy of an e has the same magnitude as the E it takes to remove that e from the atom ionize QUANTUM NUMBERS SCHR DINGER Described electron as a wave not a particle Created the wave function which supports that the E of the e is quantized 2 is related to the probability of finding the e within a given region of space To solve the wave function the three integer quantum numbers n and m are needed PRINCIPLE QUANTUM NUMBER Principle n 1 2 3 Primary factor in determining energy of an e Defines size of an orbital as n increases so does the e s average distance from the nucleus Two or more e may have the same n n number of subshells in a shell n2 number of orbitals in a shell ANGULAR MOMENTUM QUANTUM NUMBER Angular l 0 1 2 3 n 1 Determines subshell in which an e resides Each number corresponds to a different orbital shape or orbital type Value of l Corresponding Subshell Label 0 1 2 3 s p d f Value of l also specifies number of planar nodes in the orbital in any given subshell MAGNETIC QUANTUM NUMBER Magnetic ml any integer between l and l Related to the orientation in space of the orbitals within a subshell Number of m values for a given equals the number of orbitals within that subshell 2 l 1 PAULI EXCLUSION PRINCIPLE Principle no two e in a single atom may have the same exact set of quantum numbers th 4 QN Spin Quantum Number ms o Only permissible values are and o Therefore only two e can reside in a single orbital ELECTRON CONFIGURATION e CONFIGURATION Listing of e populations in various subshells of an atom Example Fluorine 1s22s22p5 Represents ground state e placement for lowest atom E Orbitals are still present when empty e e repulsion can occur giving orbitals of a given n different E Subshells are filled with e from lowest E to highest E Diagonal rule is used as a guide to subshell E ordering http www explorelearning com ELContent gizmos ELScience Deliverable Explorat ionGuides