Chapter 8: Electron Configurations and the Periodic Table Chem 6A, Section D Oct 25, 2011

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1 Chapter 8: Electron Configurations and the Periodic Table Chem 6A, Section D Oct 25, The Periodic Table of the Elements 2

2 Electron Configurations Aufbau ="Building up" As each proton is added to the nucleus, you add an electron to the hydrogen-like orbitals. Add to s, then d, then p orbitals of the same principle quantum number 3 Quantum numbers Quantum Number n l Called Principle quantum number Angular momentum (Azimuthal) quantum number Describes SIZE and ENERGY SHAPE m l Magnetic quantum number ORIENTATION m s Electron spin quantum number INTRINSIC ANGULAR MOMENTUM OF THE ELECTRON 4

3 The Periodic Table of the Elements 5 The Periodic Table of the Elements 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 5d 6p 7s 1s 6

Electron Configurations How to fill up orbitals with electrons? Electrons go in lowest energy orbital first, they spread over all the empty orbitals with the same spin, then they pair up.

4 Electron Configurations How to fill up orbitals with electrons? Electrons go in lowest energy orbital first, they spread over all the empty orbitals with the same spin, then they pair up. Pauli Exclusion Principle: No more than 2 electrons per orbital, must be of opposite spin. Hund's rule: When there is more than one orbital with the same energy, fill up empty orbitals first, keeping the spins the same. 7 The Building-up Principle (aufbau) Pauli exclusion principle: no more than 2 electrons in each orbital. Pairs of electrons in the same orbital must have opposite spins. Hund s rule: When there is more than one orbital with the same energy (degenerate), fill up empty orbitals with one electron before pairing the electrons, keep the spins the same. from T. Moeller Inorganic Chemistry Wiley 1952 Similar figure in your textbook 9 8

5 Stern-Gerlach Experiment: Ag atoms Screen OVEN Containing Ag Magnet The atoms split into two paths in a magnetic field This experiment tells us that each individual electron has a magnetic moment; there must be a 4th quantum number: Electron spin, or m s 9 Electron Configurations Example Electron configurations: Potassium 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 shorthand: [Ar]4s 1 Vanadium [Ar]4s 2 3d 3 Selenium [Ar]4s 2 3d 10 4p 4 Note: (n+1)s orbitals always fill up before nd. 4f and 5d orbitals have similar energies, Lanthanides fill up 4f and 5d orbitals in somewhat random order. Don t worry about lanthanides for now. 10

Electron Configurations 11 Electron Configurations-Exceptions Exceptions: everything fills up normally, with a few exceptions: Cr: [Ar]4s 1 3d 5 Why?

6 Electron Configurations 11 Electron Configurations-Exceptions Exceptions: everything fills up normally, with a few exceptions: Cr: [Ar]4s 1 3d 5 Why? half-filled shells are unusually stable. This one you can't predict, just memorize. Cu: [Ar]4s 1 3d 10 Why? fully-filled shells are stable. Memorize these 12

Ordering of s, p, d, and f orbitals Relative ENERGIES: s < p < d < f Fill ns, then np,

Example (V): Vanadium: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 3 You always fill up (n+1)s

13 Ordering of s, p, d, and f orbitals You always fill up (n+1)s Main factors

7 Ordering of s, p, d, and f orbitals Relative ENERGIES: s < p < d < f Fill ns, then np, then nd orbital. Example (V): Vanadium: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 3 You always fill up (n+1)s before nd. Why? 13 Ordering of s, p, d, and f orbitals You always fill up (n+1)s before nd. Why? Main factors determining relative energy ordering for orbitals with the same value of n: Nuclear charge Electron-electron repulsion (shielding) 3 s orbital 3 p x orbital 3 d xz orbital

8 Ordering of s, p, d, and f orbitals ORBITAL SHAPE: Which orbital allows the electrons to get closer to the nucleus? The electron likes to get closer to the nucleus if it can, so it goes into the s orbital before the p orbital Ψ 2 (probabbility) 1s Radial Probability Functions 2p Electron Penetration 2s has greater probability close to the nucleus than 2p 2s r, Bohr radii 15 Electron Penetration The lower the value of l, the greater the penetration. Relative ENERGIES: s < p < d < f 16

9 17 Periodic Trends ATOMIC RADII Relative size of atoms IONIC RADII Relative size of ions IONIZATION ENERGY ELETRON AFFINITY 18

10 Periodic Trends: ATOMIC RADII Fig 8.8 TREND: small on top, big on bottom shrink going L to R, because nuclear charge is increasing w/o increasing n Periodic Trends: ATOMIC RADII Fig

11 Problem: Atomic Radius Rank the following set of main group elements in order of decreasing atomic size: Br, Rb, Kr, Ca, Sr 21 Solution: Atomic Radius Rank in order of decreasing atomic size: Br, Rb, Kr, Ca, Sr Elements with n = 4: Br, Kr, Ca Size increases going L->R, so big to small is Ca > Br > Kr Elements with n = 5: Rb, Sr Size increases going L->R, so big to small is Rb > Sr 22

12 Solution: Atomic Radius Rank in order of decreasing atomic size: Br, Rb, Kr, Ca, Sr Is Sr > Ca or is Ca > Sr? Sr > Ca, so the final ranking is Rb > Sr > Ca > Br > Kr 23 Periodic Trends: IONIC RADII Fig

13 Periodic Trends: IONIC RADII Fig Periodic Trends: IONIZATION ENERGY and ELECTRON AFFINITY IONIZATION ENERGY: A A + + e - ELECTRON AFFINITY: A + e - A - They are not the reverse of each other! 26

Periodic Trends: IONIZATION ENERGY Fig 8.

14 Periodic Trends: IONIZATION ENERGY Fig Periodic Trends: IONIZATION ENERGY It is really hard to pull an electron from He Fig 8.11 It is really easy to pull an electron from Cs 28

15 Periodic Trends: ELECTRON AFFINITY Fig Periodic Trends: ELECTRON AFFINITY ELECTRON AFFINITY: Can be either exothermic or endothermic 30

16 Periodic Trends: SUMMARY Fig Periodic Trends: IONIZATION ENERGY Fig st, 2 nd, and 3 rd ionization energies for Beryllium (Be) Why is 3 rd IE so much larger than 1 st or 2 nd IE? 32

Problem: Predicting Common Oxidation States from Ionization Energy The ionization energies for lead are given below. Based on this information, predict the common oxidation states for this element.

17 Problem: Predicting Common Oxidation States from Ionization Energy The ionization energies for lead are given below. Based on this information, predict the common oxidation states for this element. 33 Lead in the Washington, DC water supply March 12, 2004 Steve Curwood radio interview with Marc Edwards on Living on Earth: D.C. WATER WOES CURWOOD: Last year, at the request of some Washington, D.C. residents, Marc Edwards, a civil engineer and corrosion specialist with Virginia Tech, began testing the quality of drinking water being piped into their homes. Soon, he says, he found concentrations of lead in that water that he describes as being literally off the charts. Some of the levels were so high that the water could be considered hazardous waste

18 Solution: Predicting Common Oxidation States from Ionization Energy IE, KJ/mol Pb + Pb 2+ Pb 3+ Pb State Pb 2+, Pb 4+ are the most common oxidation states for Pb. 35 Inert Pairs Sn 2+, Tl +, Pb 2+, Bi 3+ are stable ions, even though they do not have a noble gas configuration: Pb: [Xe] 6s 2 5d 10 6p 2 Pb 2+ : [Xe] 6s 2 5d 10 Pb 4+ : [Xe] 5d 10 The s electrons are not as easily removed in these elements--a pair of s electrons is inert Common oxides of lead: PbO, PbO 2 36

19 Lead in the Washington, DC water supply March 12, 2004 Steve Curwood radio interview with Marc Edwards on Living on Earth: D.C. WATER WOES CURWOOD: Last year, at the request of some Washington, D.C. residents, Marc Edwards, a civil engineer and corrosion specialist with Virginia Tech, began testing the quality of drinking water being piped into their homes. Soon, he says, he found concentrations of lead in that water that he describes as being literally off the charts. Some of the levels were so high that the water could be considered hazardous waste Use of monochloramine in water purification April, 1999 Guidance Manual from EPA: Use an alternative or supplemental disinfectant or oxidant such as chloramines or chlorine dioxide that will produce fewer DBPs (Disinfectant Byproducts). Monochloramine, and chlorine dioxide are typically used to maintain a disinfectant residual in the distribution system 38

Use of monochloramine in water purification Chlorine: Cl 2 + H 2 O HOCl + H + + Cl - Monochloramine: NH 3 + HOCl NH 2 Cl + H 2 O Monochloramine kills bacteria too Not as strong an oxidant as chlorine

20 Use of monochloramine in water purification Chlorine: Cl 2 + H 2 O HOCl + H + + Cl - Monochloramine: NH 3 + HOCl NH 2 Cl + H 2 O Monochloramine kills bacteria too Not as strong an oxidant as chlorine or hypochlorite Produces fewer potentially toxic or carcinogenic byproducts 39 Presence of lead in simulated drinking water 2 months after switching to chloramine disinfectant water disinfected with chlorine Rebecca Renner, ENVIRONMENTAL SCIENCE & TECHNOLOGY JUNE 15,

21 Chemistry of lead oxides Hypochlorite reaction: Monochloramine reaction: oxidation state: + 4 Pb + 2HOCl PbO 2 + 2HCl oxidation state: + 2 Pb + NH 2 Cl + H 2 O PbO + NH 3 + HCl Solubility in water: PbO: g/l at 20 C Solubility of PbO 2 << PbO 41 Acid-Base Behavior of Oxides Some metal oxides and most metalloid oxides are amphoteric (react with acid or base): acid: Al 2 O 3 + 6H + 2Al H 2 O base: Al 2 O 3 + 2OH - + 3H 2 O 2Al(OH) 4-42

22 Acid-Base Behavior of Oxides Metal oxides produce basic solutions in water: MgO + H 2 O Mg OH - Because metals are ionic Nonmetal oxides produce acidic solutions: CO 2 + H 2 O HCO H + Because nonmetals are covalent 43 Acid-Base Behavior of Oxides Metal oxides produce basic solutions in water: PbO + H 2 O Pb OH - PbO 2 + 2H 2 O Pb OH - Neither is very soluble in water, but PbO >> PbO 2 44

23 Chemistry of lead oxides Changes in ph, drops in ORP, or both could destabilize these PbO 2 films, and thus increase plumbosolvency observations that have been made by some water systems of erratic lead release from lead service lines, and increases or decreases without clear correlations with ph, DIC, and temperature, may be caused at least in part by effects of ORP changes. --Lytle, D.A. and Schock, M.R., U.S. Environmental Protection Agency, 2005 ORP = oxidation-reduction potential DIC = dissolved inorganic carbon 45 Periodic Trends Main Points: Quantum numbers summary Electron configurations for d-block elements: First-in, first-out for transition metals: ns electrons removed before (n-1)d electrons Magnetic properties of transition metal ions: paramagnetism, diamagnetism 46

24 Measurement of Magnetic Properties Fig 8.19 No unpaired electrons in compound Compound has unpaired electrons 47 Problem: Predicting Diamagnetism or Paramagnetism from Electron Configurations Possible electron configurations for the paramagnetic ion Fe 2+ are given below. Which is correct? (a) (b) (c) (d) (e) None of the above are correct 48

Electron configuration for Fe: 4s 2 3d 6 Electron configuration for Fe 2+ : 3d 6 Solution: Predicting Diamagnetism or Paramagnetism from Electron Configurations Always remove (n+1)s electrons before

25 Electron configuration for Fe: 4s 2 3d 6 Electron configuration for Fe 2+ : 3d 6 Solution: Predicting Diamagnetism or Paramagnetism from Electron Configurations Always remove (n+1)s electrons before nd electrons when you make ions. How to place electrons in the d orbital? Follow Hund s rule: 49 Solution: Predicting Diamagnetism or Paramagnetism from Electron Configurations So (c) is the correct answer: Fe 2+ How many unpaired electrons in Fe 2+? 4 50

Electron Configuration and Chemical Periodicity

Electron Configuration and Chemical Periodicity The Periodic Table Periodic law (Mendeleev, Meyer, 1870) periodic reoccurrence of similar physical and chemical properties of the elements arranged by increasing