Chemistry Lecture Notes Periodic Trends

1. Chemistry Lecture Notes Periodic Trends

2. Diamonds from cremations Christian Wamser of Camillus, NY, was intrigued by a report in the Syracuse, NY, Post-Standard that a Chicago woman had become “the first person in the world to have the carbon from her body transformed into diamonds.” The Chicago company, LifeGem, is working to patent and process for extracting the carbon from cremated bodies and pressing it into diamonds. LifeGem’s plan is to offer its service through funeral homes. The company would extract the carbon from cremated remains and ship it to a facility in Germany that presses it at 3,000°C for eight weeks. The Chicago woman’s remains, says LifeGem, yielded six half-carat diamonds that were given to her family. All diamonds, the company says, are certified by the Gemological Institute of America.

3. The Business of Death … LifeGem uses a advanced high-nitrogen, low-oxygen technique to turn the carbon from cremated remains into a diamond for memorial rings or necklaces. Formed in 2001, the Elk Grove Village, IL-based company charges anywhere from $2,699 to $18,999, depending on the size and cut of diamond, and expects sales this year to reach $7.5 million. Wearing the diamonds, says one customer, helps “celebrate life, rather than mourn death.” www.lifegem.com

4. Valence (outer shell) electrons: electrons in shell of highest n Core (inner shell) electrons: electrons below outer shell N [He]2s22p3 core valence Fe [Ar]3d64s2 core valence • Effective nuclear charge, Zeff • Zeff = Z - S number of inner shell electrons number of protons

5. Periodic trends: atomic radius smallest atom atomic radius decreases largest atom 1. across: Zeff increases, electrons attracted more strongly (no. of protons increases while no. of core electrons remains constant) least attraction, largest radius greatest attraction smallest radius

6. transition metals: Zeff ~ constant • e.g. third row: [Ar]3dx4s2Zeff = 2 core valence • -each additional proton accompanied by another core electron • radius ~ constant 2. up-down: shells grow larger with increasing n (Zeff constant within a group) • Which is larger? • N or P Al or Si Na or Be N or Cl

9. Periodic trends: ionization energy Energy required to remove an electron from an atom: A  A+ + e– highest I.E. I.E. increases (generally) lowest I.E. across: Zeffincreases, electrons held more tightly (~ constant through transition metals) up: valence electrons in lower energy orbitals, take more energy to remove

12. A  A+ + e– 1st I.E. • A+  A2+ + e– 2nd I.E. • etc. • successive ionization energies increase • large increase when number of valence electrons = noble gas

13. Which has the higher ionization energy? • B or C K+ or Ca+ • Na or K Mg2+ or Al2+

14. Periodic trends: electron affinity electron affinity: A + e– A– highest E.A. E.A. increases (generally) lowest E.A. across: Zeffincreases, electrons attracted more strongly up: electrons go into lower energy orbitals, E.A. more exothermic

16. Electronic configurations of ions • Na Cl • Na+ Cl– • Ca O • Ca2+ O2– • Transition metal cations: remove electrons from shell of highest n first, • then start removing from orbitals of lower n: • Fe Zn • Fe2+ Zn2+ • Fe3+ • Ag • Ag+

17. Chemical properties of the elements: octet rule • representative metals: tend to lose enough electrons to achieve theprior noble gas configuration • nonmetals: tend to gain enough electrons to achieve the next noblegas configuration • noble gases: tend not to lose or gain electrons • alkali metals ns1 +1 ions noble gas configuration: • alkaline earth metals ns2 +2 ions ns2np6 = octet • chalcogens ns2p4 -2 ions • halogens ns2p5 -1 ions • noble gases ns2p6 full octet • transition metals: variable

18. Reducing agent: gives up electrons Mg + Ni2+ Mg2+ + Ni (Ni2+ is reduced) Ag + Ni2+  no reaction Ionization energy decreases Electron affinity decreases (Strongly affected by solution effects)