Understanding Electron Configuration and Periodic Trends
School
Purdue University**We aren't endorsed by this school
Course
CHEM 129
Subject
Chemistry
Date
Dec 12, 2024
Pages
31
Uploaded by SuperFreedomDolphin42
Lecture 6 – 09.02.2022Agenda•Exceptions to Electron Configuration•Understanding Periodic Trends in the Chemical and Physical Properties of the Elements:•Valence electrons•Shielding & effective nuclear charge•Atomic radius•Ionization energy
•CONNECT HW #1 this Sunday, 09/04/2022 by 11:59pm. •CONNECT HW #2 Sunday, 09/11/2022 by 11:59pm. •Next week -Lab 2: Iron Deficiency Analysis. You are required to write out a procedure … make sure these are your own words!•Lab reports are submitted as a group to GradescopeLecture #6 ( Fri. 09.02.2022)Announcements
Inner (______) electronsare those an atom has in common with the previous noble gas (and any completedtransition series).Outer electronsare those in the highestenergy level (highest nvalue).__________ electronsare those involved in bonding.chemical bondingØFor main groupelements, the valence electrons arethe outer electrons.ØFor transition elements, the valence electrons include the outer electronsand any (n-1)delectrons. (less useful designation than for main group elements)Categories of Electrons
Similarity of valence electron configurations help predict chemical properties.For Group 1A: [noble gas]ns1valencecoreFor Group 2A: [noble gas]ns2valencecoreFor Group 7A: [noble gas]ns2np5valencecoreValence ElectronsThe number of valence electrons is the ________________ for the representative elementsAll valenceelectrons available for bonding!
ns1ns2ns2np1ns2np2ns2np3ns2np4ns2np5ns2np6d1d5d104f5fGround State Electron Configurations of the ElementsSimilar valence electron configurations correlate with similar chemical behavior.
Similar Reactivities in a GroupPotassium reacting with water.Chlorine reacting with potassium.Similar valence electron configurations correlate with similar chemical behavior.
Practice QuestionConsider the element Neon. Which of the following statements is incorrectregarding its electron configuration?A.Neon has 8 valence electronsB.Neon has full 2s orbitalsC.Neon has full 2p orbitalsD.Neon has full d orbitalsE.All statements are correct
Periodic Trendsof the ElementsEffective Nuclear ChargeAtomic RadiusIonization EnergyElectron AffinityThe electron configuration of the elements affects their ________ & chemical properties
•The energies of atomic orbitals are affected by–______________ (Z) and–shieldingby other electrons.•A higher nuclear chargeincreases nucleus-electron interactions and lowers sublevel energy.•Shieldingby other electrons reduces the full nuclear charge to an effective nuclear charge(Zeff).–Zeffis the nuclear charge an electron actuallyexperiences.•Orbital shapealso affects sublevel energy.Factors Affecting Atomic Orbital EnergiesIn a multi-electron atom, electrons are simultaneously attractedto the nucleus and repelledby one another.
The Effect of Nuclear Charge on Sublevel EnergyGreater nuclear charge _______sublevel energy.It takes more energyto remove the 1selectron from He+than from H.
Shielding and Orbital EnergySecond electron feels the full effect of the +2 charge and is more ___________________________Core electrons are the most effective in shielding.
•Electrons in the sameenergy level shield each other to some extent.•Electrons in ______energy levels shield the valence electrons very effectively.– The further from the nucleus an electron is, the lower the effective charge (Zeff) felt by that particular electron.Shielding and Orbitals
Effective Nuclear Charge (Zeff)non-valence, core electrons are the most effective at shielding# core electrons stays the same# of protons and valence electrons increasesZeff felt by valence electrons _________ from left to right across a period
Effective Nuclear Charge (Zeff)increasingZeffZeffincreases down a group but ______ significantlyThe large increase in nuclear charge is offset by the increase in shells of core electrons used for shielding.
Periodic Trends in Atomic RadiusØAtomic size increasesas quantum number nincreases.ØAs nincreases, the probability that the outer electrons will be further from the nucleus increases.ØAtomic size decreasesas Zeffincreases.ØAs Zeff(effective nuclear charge) increases, the outer electrons are pulled closer to the nucleus.ØFor main group elements: atomic size increasesdown a group in the periodic table and decreasesacross a period.Atomic _______is the distance between the nucleus of an atom and its valence shell. But quantum theory tells us we can’t absolutely position electrons.
Atomic Radius Periodic TrendsAtomic radius__________ left to right across a period due to increased electrostatic attraction between the effective nuclear charge and the charge on the valence shell. Valence shell drawn closer, radius smaller.Coulomb’s Law:The magnitude of the electrostatic force (F) on a charge (q1) due to the presence of a second charge (q2), r is distance between objectsThere is a stronger attraction between the charges in the nucleus and the valence shell electrons when the magnitude of both increases
Trends in Atomic Radii
Ranking Elements by Atomic SizePROBLEM:Using only the periodic table, rank each set of main-group elements in order of decreasingatomic size:(a)K, Ga, Ca(b)Sr, Ca, Rb(a)_________________(b)_________________
Practice QuestionArrange the set of main-group elements in order of decreasingatomic sizeBr, Rb, KrA.Rb > Br > Kr B.Kr > Rb > Br C.Br > Kr > RbD.Kr >Rb > Br
___________ energyis the minimum energy (kJ/mol) required to remove an electron from a gaseous atom in its ground state.I1+ X (g)X+(g)+ e-I2+ X+(g)X2+(g)+ e-I3+ X2+(g)X3+(g)+ e-I1first ionization energyI2second ionization energyI3third ionization energyI1< I2< I3IE1(Na) = 495.8 kJ/mol.Na(g) → Na+(g) + e−Ionization Energy
Trends in Ionization EnergyIonization energy (IE)is the energy required for the complete removalof 1 mol of electrons from 1 mol of gaseous atoms or ions.Atoms with a low IEtend to form ________, ions with positive charge.Atoms with a high IE tend to form anions, ions with negative charge.Noble gases have very high IE, are very stable and do not tend to ionize – have a completely full valence shell.
Group Trends in First Ionization EnergiesDECREASING First Ionization Energy•Ionization energy decreases top to bottom within a group•______ doesn’t change significantly as you go down a group•Radius increasesas n increases•Coulomb’s law: greater distance between a valence e- and Zeff, attraction gets weaker and the e- is easier to remove (IE goes down)
Ionization EnergyIn general, as Zeffincreases, ionization energy also increases.•Coulomb’s law: greater charge magnitude (Zeff), valence e-are more strongly attracted to nucleus and the e-is harder to remove (IE goes up)•Thus, IE1increases from left to right across a period.Filled n=1 shellFilled n=2 shellFilled n=3 shellFilled n=4 shellFilled n=5 shell
Trends in Ionization EnergyIonization energy tends to decreasedown a group and increaseacross a period.Interruptions in the trend explained by electron configurations.ØCompletely filled and half-filled subshells are more stable than might otherwise be expectedThe overall trends in ionization energy are ________ to those for atomic radii.
First Ionization Energies of the Main-Group Elements – Exceptions to the Trendnp3> np4e.g.7N > 8OAfter the separate degenerate orbitals have been filled with single electrons, the fourth electron must be paired.The electron-electron ___________ makes it easier to remove the outermost, paired electron.
First Ionization Energies of the Main-Group Elements – Exceptions to the Trendns2> np1e.g. 4Be > 5BEnergy of e-in an nporbital is > e-in its respective nsorbital._______________Less energy required to remove the first electron in a p orbital than it is to remove one from a filled s orbital.e-held less tightly by the nucleus and easier to remove.
Practice QuestionArrange the elements Mg, Cl, P, Rb in order of increasing IE1.A.Cl < P < Rb < MgB.Mg < P < Rb < Cl C.Cl < P < Mg < RbD.Rb < Mg < P < Cl
oIt is possible to remove additional electrons in subsequent ionizations.o_________to remove an electron from a cationoMuch more difficult to remove a core electronthan a valence electronoCore electrons are closer to the nucleusoCore electrons experience greater Zeffbecause there are fewer filled shells shielding them from the nucleus.Second Ionization EnergyNa(g) → Na+(g) + e−IE1(Na) = 496 kJ/mol.1s22s22p63s1 1s22s22p6IE2(Na) = 4562 kJ/mol.Na+(g) → Na2+(g) + e−1s22s22p61s22s22p5
The First Three Ionization Energies of BerylliumBeryllium has 2 valence electrons, so IE3is much larger than IE2.
CHM129 Lab 2: Iron DeficiencyProper Lab Clothing1.You must have completed your Safety Certification to participate2.You must have turned in your Prelab #2 to participate3.You must have goggles and proper clothing or you will be sent home4.Lab #1 Report due at the beginning of Lab #2What’s going on:GOGGLES MUST BE WORN AT ALL TIMESEVEN WHEN WRITING NOTES & REPORTSNo skin should be exposed onankles, collar bones, or shoulders
Lab 2: Iron DeficiencyWhat is the concentration of Fe2+in serum?Using a standard curve to determine an unknownPrelab #2:1) Unit conversions2) Calculate concentrations using mole ratios3) Determine an unknown from a standard curve4) Write a procedure summary1) Make Fe2+·Ferrozine standards2) Measure absorbance3) Make abs. vs. conc. standard curve4) Measure abs. of unknown5) Calculate Fe2+using yourstandard curveLab #2: Make standard curve and determine unknown serum Fe2+Blank1234Unknown???y = 0.0051x - 0.0181R² = 0.99250.00.20.40.60.81.0050100150200Absorbanceat 560 nmFe2+ Concentration (ug/dL)Absorbance vs. Fe2+Concentrationy = 0.0051x - 0.0181R² = 0.99250.00.20.40.60.81.0050100150200Absorbanceat 560 nmFe2+ Concentration (ug/dL)Absorbance vs. Fe2+ConcentrationChemical Safety & Waste:1) If you spill/drip HClYOU ARE RESPONSIBLEfor cleaning it up!2) Ferrozine solutions must be disposed in thewaste container, not down the sink drain