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Lesson 23-26

by: Corymarie Notetaker

Lesson 23-26 CHMY 141N - 00

Corymarie Notetaker
College Chemistry I
Mark Cracolice (P)

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About this Document

These notes include lessons 23-26 with the main ideas, helpful hints, and vocabulary from the lessons.
College Chemistry I
Mark Cracolice (P)
Class Notes
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This 12 page Class Notes was uploaded by Corymarie Notetaker on Saturday November 7, 2015. The Class Notes belongs to CHMY 141N - 00 at University of Montana taught by Mark Cracolice (P) in Fall 2015. Since its upload, it has received 29 views. For similar materials see College Chemistry I in Chemistry at University of Montana.

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Date Created: 11/07/15
CHMY 141 Notes Lesson 23 26 LESSON How are Electrons Distributed Within an Atom Electromagnetic radiation a form of energy that consists of both electric and magnetic fields and travels at the speed of light 0 has wavelike properties Electromagnetic Spectrum Speed of Light c 300x108 meters per second waves can be mathematically described by a wave equation Every wave can be described by its properties 0 wavelength A the distance between identical parts of a wave units typically meter m 0 frequency v number of complete waves passing a point in a given period of time units hertzHz1second o velocity v or c related to a waves wavelength and frequency cvA units metersecond I since the speed of light is essentially a fixed quantity the wavelength and frequency of electromagnetic waves are inversely proportional The longer the wavelength the shorter the frequency and vise versa 1900 Max Planck a German theoretical physicist o the nature of the relationship between the intensity of the light emitted by a heated object and its frequency was explained by Planck by stating that the energy of the electrons in the atoms of the material is directly proportional to their frequency 0 Ehv where h is Planck39s constant and has a value of 6626x103934 0 Albert Einstein improved on Planck39s idea by proposing that energy is released in photons Photon a particle of light massless packet of electromagnetic radiation wavelike duality light particles also have wavelike properties 0 light has properties that have no analogy at the macroscopic level and thus we have to combine two different ideas to describe its behavior 0 Planck39s quantum concept tells us that light is not a continuous flow of radiation but rather a series of individual photons LESSON How are Electrons Distributed Within an Atom Planck39s quantum concept tells us that even though energy appears to be smooth and continuous on our humansized scale it really is made up of tiny individual packets of energy too small for our senses Einstein s formulation of the concept of photons came from his consideration of the experimentallyobserved photoelectric effect which shows that the photoelectric effect depends on the frequency of the light shined on the metal surface 0 can be explained by the wave model I if light is a particle and light particles strike a metal surface then particles with low energies low frequency will not have sufficient energy to eject electrons and there will be a certain energy frequency threshold at and beyond which the light particles will have sufficient energy to eject electrons Also the brightness number of light particles of the light will not have a significant effect on the time needed to initiate electron ejection but it will be proportional to the number of electrons ejected I energy of a photonenergy needed to eject electron kinetic energy of electron after ejection Einstein39s model was verified by Millikan39s experiments Electron s arrangement 0 Quantized energy possessed by an electron of an atom that is limited to specific values it can never be between two of those values 0 Continuous energy possessed by an electron of an atom that can have any value between any two values there is an infinite number of other acceptable values A line spectrum is quantized but white light is continuous Quantized energy levels at any instant the electron may have one of several possible energies but at no time may it have an energy between them The process by which an electron moves between orbits is called a quantum jumpquantum leap The electron is normally found in its ground state the condition when all electrons in an atom occupy the lowest possible energy levels I an electron can be raised to an excited state the condition at which one or more electrons in an atom has an energy level above ground state An electron in an excited state is unstable I When the electron falls back to ground state it releases a photon of light energy with a frequency proportional to the energy difference between the two levels This energy release appears as a line in the spectrum of the element I energy of the electron E RHx 1 where RH is the Rydberg constant 21798722x10 18J LESSON How are Electrons Distributed Within an Atom The Quantum Mechanical Model waveparticle duality when in motion an electron has wavelike properties and particlelike properties when interacting with another particle In 1924 Louis de Broglie proposed that all particles have a wavelength when in motion 0 the wavelength of any moving particle is A hmv I where A is the de Broglie wavelength h is Planck s constant m is the mass of particle and v is its velocity An electron travels in a wave while in a circular orbit When the wave makes one or more complete revolutions it must match exactly the position of its starting point This means that the circumference of the orbit must be exactly equal to the wavelength or nany integer amount greater 0 Therefore the orbital circumference are quantized the circumferences have only certain values and never a value in between two quantized values I when n1 there is one wavelength per orbit I wavelength for an electron is very large compared to the size of the atom Werner Heisenberg proved that it is impossible to simultaneously know both the position and the velocity of an electron or other small particle o the more accurately one quantity is known the greater the uncertainty in the other factor 0 mathematical statement of the Heisenberg Uncertainty Principle I AxmAv 2 h411 I where Ax is the uncertainty in position m is mass Av is uncertainty in velocity and h is Planck39s constant Schrodinger applied the principles of wave mechanics to atoms and developed the quantum mechanical model of the atom o Schrodinger wave equation formulated an equation that is the fundamental scientific law used to understand how the wavelike properties of electrons affect their behavior I wave function of an electron the unknown in the equation that must be solved for Essentially the mathematical description of the wave The square of the wave function is the probability density of the electron This is the probability of finding the electron is a 3dimensional region of space I Quantum mechanics tells us that that we cannot precisely predict the position of an electron we can only determine the probability of finding it within a certain set of distances from the nucleus LESSON How are Electrons Distributed Within an Atom The Quantum Mechanical Model Quantum mechanics gives us orbitals regions in space where an electron is likely to be found at a certain probability level rather than the deterministic orbits of the Bohr model However it keeps the quantized energy levels that were introduced by Bohr o Orbitals probability density for an electron Quantum numbers four quantities to describe electron energy 0 the principal energy level energy level n1237 I energy increases as the level increases 0 the sublevel each principal energy level has n sublevels designated by O12n1 Values depend on value of n I O123spdf I energies increase in the order s p d f o the orbital electron orbital quantum number has the symbol me I possible values are me 43 0 8 depending on value of 8 80 me O s has 1 orbital 81 me 1 0 1 p has 3 orbitals 82 me 2 1 0 1 2 d has 5 orbitals o the number of electrons in an orbital ms and I Pauli exclusion principle limit the population of any orbital to two electrons orbital can have 0 1 or 2 electrons LESSON How are Electrons Distributed Within an Atom The Quantum Mechanical Model Sublevel Orbitals Maximum Electrons per Sublevel s 1 1322 p 3 3326 cf 5 10 f 7 14 Sublevel Letter Quantum Designation Number 0 3 3 19 i2 cf i3 f LESSON How are Electrons Distributed Within an Atom The Quantum Mechanical Model n Number of Sublevels l 1 Z Z 3 3 4 4 5 5 6 6 7 7 Identification of Sublevels ls 252p 353p3d 4s4p4d4f 555p5d5 5g 656p6 6 6g6hl 7s 7p 7d 7r 7g 7h 7n lESSDll Howare Electrons Distributed Among Orbitals Within an Atom The disTribuTion of eecTrons wiThin an aTom deTermines how ThaT aTom will bond To oTher aToms To form molecules ElecTron configuration The groundsTaTe disTribuTion of eecTrons among The orbiTals of a gaseous aTom Two rules guide The assignmenTs of eecTrons To orbiTals o aT ground sTaTe The eecTrons fill The owesT energy orbiTals available 0 no orbiTal can have more Than Two eecTrons The periodic Table is a guide To The order of increasing sublevel energy 0 menTally divide The periodic Table inTo four blocks I sblock Groups 1A and 2A period 1 in The 5 block corresponds To n1 I pblock Groups 3A Through 8A period 2 3 4 in The s and p blocks correspond To n 2 3 4 I dblock The B Groups begins wiTh n3 I fblock anThanides and The acTinides begins wiTh n4 41 are anThanides and 51 are acTinides Groups 1A1 and 2A2 The s subeves are The highesT occupied The p orbiTals are filled in order across Groups 3A13 To 8A18 The d eecTrons appear in The B groups 3 To 12 The f eecTrons show up in The anThanide and acTinide series The ToTa number of eecTrons in any sublevel is shown by a superscripT number Using The periodic Table as a guide eecTron configuraTions can be wriTTen for elemenTs 0 ex H is1 Na lsZZsZZp Bs1 InsTead of wriTing long eecTron configuraTions a noble gas core is used replacing The long eecTron configuraTion middle of an elemenT 0 ex Na Ne3s1 InTerrupTions appear aT chromium Cr Ar4523d4 and copper Cu Ar4513d10 OrbiTal diagram a diagram ThaT shows how many eecTrons are in each orbiTal 0 you show The locaTion of each eecTron by drawing boxes represenTing orbiTals An orbiTal occupied by one eecTron is indicaTed by drawing in The box a half arrow poinTing up Two eecTrons is shown by Two half arrows one poinTing up and one down 0 When There is more ThaT one orbiTa for a given 8 value you puT The eecTrons in The boxes one aT a Time aT firsT Then add addiTional eecTrons To The orbiTals doubling up if necessary lESSDll Howare Electrons Distributed Among Orbitals Within an Atom Hund s rule The mosT sTable arrangemenT of eecTrons in a sublevel is The one ThaT has The maximum number of unpaired eecTrons o The normal pracTice is To use noble gas cores wiTh orbiTal diagrams To allow focus on The orbiTals ThaT are halffilled or empTy valence elecTrons relaTed To The ToTa number of s and p elecTrons in The highesT occupied energy level 0 Group 1A elemenT have ns1 of The highesT occupied principal energy level all have one valence elecTron 0 Group 5A have The general configuraTion of nsznp3 all have five valence elecTrons O NoTice ThaT for every group The number of valence elecTrons is The same as The group number AnoTher way To show valence elecTrons uses Lewis39s symbols which are also called elecTron doT symbols Procedure How To WriTe ElecTron ConfiguraTion o STep one LocaTe The elemenT in The periodic Table From iTs posiTion in The Table idenTify and wriTe The elecTron configuraTion of iTs highesT occupied energy sublevel Leave room for wriTing lowerenergy sublevels To iTs lefT STep Two To The efT of whaT has already been wriTTen lisT all lowerenergy sublevels in order of increasing energy STep Three For each lowerenergy sublevel wriTe as a subscripT The number of eecTrons ThaT fill ThaT sublevel There are Two 5 elecTrons ns2 six p elecTrons nsquot and Ten d elecTrons ndlo ExcepTions for chromium and copper The 45 subeve has only one elecTron 4s1 o STep four Confirm ThaT The ToTal number of eecTrons is The same as The aTomic number LESSON Howare Electrons Distributed Among Orbitals Within an Atom Group 1A 2A 3A 4A 5A 6A 7A 8A 3 electrons 1 2 p 1 2 3 4 5 6 electrons Electron ns1 ns2 np1 np2 np3 np4 np5 np6 configuration Group 38 4B 5B 6B 78 lt 88 gt 1B 28 Cl electrons 1 2 3 5 5 6 7 8 1O 10 Electron 3d1 3d2 3d3 3d5 3d5 3d6 3d7 3d8 3d 3d configuration LESSON What Causes Periodic Trends in Properties of Elements 0 Effective nuclear charge Zeff the charge experienced by an electron in a manyelectron atom o can be estimated by subtracting the number of electrons in the noble gas core of an atom from the total number of electrons in the atom 0 Atom Sizes o There are two primary influences on the size of atoms highest occupied principal energy level and effective nuclear charge o moving down the periodic table n so atomic size generally increases from top to bottom on the periodic table o moving across a period principal energy level remains the same but effective nuclear charge increases thus decreasing atomic size from left to right across the periodic table 0 Size of Ions o cation ion always significantly smaller than its parent atom o anions are always significantly larger than their parent atoms o isoelectronic means same number of electrons O Ionization Energy the energy required to remove one electron from a gaseous atom of an element o ionization energy generally decreases from top to bottom on the periodic table o increases from left to right on the periodic table 0 Second ionization energy always higher than the first ionization energy 0 Electron af nity the change in the energy that occurs when an electron is added to a gaseous atom or ion o increasingly greater change in energy from left to right 0 adding an electron to an atom is an exothermic process and becomes more exothermic from left to right across the periodic table o no significant periodic trend top to bottom on the periodic table LESSON What Causes Periodic Trends in Properties of Elements Metal an element that has a tendency to lose electrons in reaction and form a positive ion o stairstep line on the periodic table separates metals from nonmetals o elements at the division are called metalloids B Si As Te At Ge Sb Alkali Metals Group 1A elements All have ns1 valence electron configuration Form 1 ion Alkaline Earths Group 2A elements All have ns2 valence electron configuration Form 2 ion Halogens Group 7A elements All have a ns2np5 valence electron configuration Form 1 ion Noble Gases Group 8A elements All have ns2np6 valence electron configuration Are not reactive Hydrogen 1s1 configuration Has properties of alkali metal and halogen families however doesn t fit with any chemical family so must be considered by itself


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