Download INTRODUCTION TO MINERALOGY 1

INTRODUCTION TO MINERALOGY
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Constitution of atoms: neutrons (0), protons (+), and electrons (-)
me = (1/1837)mp
Atomic mass = nn + np
Atomic number = np (= ne)
Isotopes = equal atomic number, unequal mass (nn)
Radioactivity: instable isotopes decay spontaneously
Halflife is a constant for an isotope
INTRODUCTION TO MINERALOGY
Three types of the radioactive decay:
Ejection of an α particle: 23892U → 23490Th + α + γ + energy
Emission of an electron: 8737Rb → 8738Sr + β + energy
Electron capture: 4019K → 4018Ar + γ + energy
Isotope fractionation by geological processes (due to mass
difference)
Additional reading: Sen (pp. 516-525) Marshak (383-386 + 718-719)
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INTRODUCTION TO MINERALOGY
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Sizes
Diameter of the nucleus ∼ 1/10 000 interatomic distance
Atomic volume belongs virtually to electrons
Electron density in a part
of the crystal structure of
tennantite. Contour at
5 e-/Å3.
INTRODUCTION TO MINERALOGY
Quantum numbers of electrons
n = principal quantul number
l = azimuthal quantum number
(from 0 to n-1)
m = magnetic quantum number
(from –l to l)
s = spin quantum number
(+1/2 or –1/2)
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INTRODUCTION TO MINERALOGY
Periodic system
Chemical properties repeat because the composition of the
outer shell is similar
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INTRODUCTION TO MINERALOGY
Mineraler som kan ses på Kullen
kvarts - SiO2
mikroklin - KAlSi3O8
plagioklas - (Na,Ca)Al(Si,Al)Si2O8
granat (pyrop-almandin) - (Mg,Fe)3Al2Si3O12
biotit - K(Mg,Fe)3AlSi3O10(OH)2
hornblende - (Ca,Na)2-3(Mg,Fe,Al)5Si6(Si,Al)2O22(OH)2
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INTRODUCTION TO MINERALOGY
Chemical bond
Atomic pair
Typical bond
distance
Sum of orbital radii*
Na – Cl
2.83
1.71 + 0.73
Si - O
1.61
1.068 + 0.45
Al – O
1.74-1.88
1.312 + 0.45
Mg – O
2.07
1.279 + 0.45
Ca - O
2.35
1.69 + 0.45
*outer
shell, all values in Å
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INTRODUCTION TO MINERALOGY
Valence
(number of electrons involved in bonding)
Electron donors and electron acceptors
Bond pair
Electron configurations
cation
Anion
Na-F
Na1s22s22p63s1
F1s22s22p5
Na+
F-
Ti-C
Ti1s22s22p63s23p63d24s2
C1s22s22p2
Ti+4
C-4
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INTRODUCTION TO MINERALOGY
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Chemical elements show different affinities to each other in
bonding, and chemical bonding produces different kinds of
relations. How do we systematize them?
INTRODUCTION TO MINERALOGY
Electronegativity
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INTRODUCTION TO MINERALOGY
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Three ”types” of chemical bonds are the three extreme cases of valenceelectron behaviour in one and the same phenomenon called the chemical bond.
Ionic bond
Covalent bond
– valence electrons
- valence electrons
of cation spend
are shared, circle
their time at anion
both nuclei
Both can give hard materials
Metallic bond
- special kind of covalent
bond. Valence electrons
are shared, but move far
from nuclei, and can be
delocalized giving
electric conductivity.
INTRODUCTION TO MINERALOGY
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Van der Waals bond: atractive force between atoms which is
purely electrostatic in the nature and does not depend on
valence electrons.
The crystal structure of ice(I)
red are the hydrogen bonds.
This is a snapshot of the
structure, because the
hydrogens hop around, and
spend ¼ of their time along
any one of the tetrahedral
directions.