Transcript Elemental Behavior

Z = proton number = atomic number
N = neutron number
A = mass number (Z+N)
Atomic mass of nuclide = (rest mass – binding energy) relative to 1/12 mass of 12C
atom, measured in atomic mass units – amu’s (must be looked up)
Atomic weight of element = sum of the masses of the isotopes of that element
times their atomic abundance (found in most textbooks)
Electrons & orbitals
•Pauli exclusion principle
•Hunds rule
•Aufbau principle
More stable:
Filled shells
Filled subshells
Filled and half
filled orbital
types
•Charges
•Ionization
potential
S and px, py and
pz orbitals
Ionization potential =
energy required to
remove an electron
Electron affinity
= energy given
off when adding
an electron to a
neutral atom
Electronegativity =
(sum of IP & EA) x
constant
Electronegativity
difference of 1.7 =
50% ionic
character
Electronegativity differences:
>2.1 - high ionic character (electrons exchanged)
Examples:
<0.5 - nonmetals - non -polar covalent bond
halite, Mg-O, Ca-O, K-O, Na-O bonds in silicates,
carbonates and other oxidiized complex anions
Fe-O, also Ti, V, Cr-O bonds in silicates
Rare (except for Si-O)
Fe-S, also Ni, Cu, Pb, Hg bonds in sulfides
also C-O, S-O, Si-O, P-O, N-O in complex ions
Graphite, sulfur, realgar, orpiment,
<0.5 - high electronegativity metals
Gold, silver, platinum group, metallic bonding
1.6-2.1 - metal and non-metal - weak ionic character
1.6-2.1 - nonmetals - polar covalent bond
0.5-1.6 - polar covalent bond
Goldschmidt’s classification
Covalent bond character – hybrid orbitals form
Ionic bonding
produces closepacked structures.
There is a balance
between attraction
of oppositely
charged ions and
repulsion by outer
electrons on both.
Radius ratio =
radius of
cation/anion in a
bond. This
determines the
coordination
number
Ionic Radii
Crystal field splitting
– orbitals change energy
in a surrounding crystal
lattice
Leads to high spin
(larger radius) and
low spin electron
configurations
Produces
color in
minerals
(example Fe+3 with 5 d electrons)
Common silicates
and oxides:
CN = 4 (Si, Al)
CN = 6 (Mg, Fe)
CN = 8 (Ca, Na)
In mantle:
olivine,
orthopyroxene,
clinopyroxene,
spinel, garnet
In the earth, abundant elements form minerals with specific coordination
polyhedra or sites. Minor elements either substitute or form rare minerals.
Contours are
enrichment in
crust/mantle
The ability to substitute is controlled by:1) radius; 2) charge (valence);
3) electronegativity (bonding behavior)
Mineral/melt
partition or
distribution
coefficients
KD = concentration in mineral
concentration in liquid
Eu has two valences:
Eu+2 and Eu+3
Ionic radius
You can calculate partition coefficients for any element in any
mineral from the radius of the mineral site and elastic
properties of the mineral.
Continental crust is complement to depleted mantle
Bulk partition coefficient = sum of each mineral Kd X the abundance of
the mineral during melting or crystallization
Bulk Kd > 1 – element is compatible, Bulk Kd < 1 - incompatible
Increasing compatibility for mantle melting
Kinds of incompatible trace elements:
Rb, K, Ba, Sr = large ion lithophile elements (LILE)
Th, U, Zr, Hf, Nb = high field strength elements (HFSE)
(Field strength = charge/ionic radius)
Water and Aqueous solutions
Ionic
potential
= field
strength
= charge/
radius
Residence time = Total mass of element in reservoir (oceans)/influx
Grams/(grams/year)
Fluid mobile elements (FME) = Rb, Ba, K, Pb, Sr
Fluid immobile elements = Nb,Ta, Zr (Hf), Ti
Basalts from subduction zones – island arc basalt