Chemistry Lecture Notes

Periodic Trends

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.

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

Valence (outer shell) electrons: electrons in shell of highest nCore (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 electronsnumber of protons

atomic radiusdecreases

smallestatom

largestatom

1. across: Zeff increases, electrons attracted more strongly (no. of protons increases while no. of core electrons remains constant)

Li Be B C N O F # protons 3 4 5 6 7 8 9 # core e

s 2 2 2 2 2 2 2

Zeff 1 2 3 4 5 6 7

least attraction,largest radius

greatest attractionsmallest radius

Periodic trends: atomic radius

transition metals: Zeff ~ constant

e.g. third row: [Ar]3dx4s2 Zeff = 2core valence

-each additional proton accompanied by another core electronradius ~ 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

I.E. increases(generally)

highestI.E.

lowestI.E.

across: Zeff increases, electrons held more tightly (~ constant through transition metals)

up: valence electrons in lower energy orbitals, take more energy to remove

Energy required to remove an electron from an atom: A A+ + e–

Periodic trends: ionization energy

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

Which has the higher ionization energy?

B or C K+ or Ca+

Na or K Mg2+ or Al2+

E.A. increases(generally)

highestE.A.

lowestE.A.

across: Zeff increases, electrons attracted more strongly

up: electrons go into lower energy orbitals, E.A. more exothermic

electron affinity: A + e– A–

Periodic trends: electron affinity

Na ClNa+ Cl–

Ca OCa2+ O2–

Transition metal cations: remove electrons from shell of highest n first,then start removing from orbitals of lower n:

Fe ZnFe2+ Zn2+

Fe3+

AgAg+

Electronic configurations of ions

• 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 = octetchalcogens ns2p4 -2 ionshalogens ns2p5 -1 ionsnoble gases ns2p6 full octet

• transition metals: variable

Chemical properties of the elements: octet rule

Ioni

zatio

n en

ergy

dec

reas

es

Elec

tron

affin

ity d

ecre

ases

Reducing agent: gives up electrons

Mg + Ni2+ Mg2+ + Ni(Ni2+ is reduced)

Ag + Ni2+ no reaction

(Strongly affected by solution effects)