Transcript Lecture 02 Elements and Ions mod 7

Last Time

We saw that minerals are crystals, and
crystals are made of unit cells,
arrangements of atoms that, when stacked
in 3 dimensions, form the complete crystal
Last Time

The edges of the unit cells, and therefore
the crystal, are parallel to a system of
crystal axes. Positive a is to the front, b to
the right, and c is up.
The angle between b and c is called a,
the angle between a and c is called b, and
the angle between a and b is called g
The most pronounced zone is
oriented vertically and an axis
parallel to that zone is called c
Once c is selected,
other axes are
drawn parallel to a
prominent face

Last Time
Six or seven crystal systems cover all possibilities
=
Last Time

We also worked out a notation for the
orientation of a crystal face, Miller Indices,
and learned how to plot them on a plane
http://www.gly.uga.edu/Schroeder/geol6550/millerindices.html
Lecture 2
Crystal Chemistry
Part 1:
Composition of the Earth
Elements, and Ions
Chemical Layers of the Earth
SiO2 – 45%
MgO – 37%
FeO – 8%
Al2O3 – 4%
CaO – 3%
others – 3%
Fe – 86%
S – 10%
Ni – 4%
Earth radius ~4000 miles, core about half way down (1800 miles)
Composition of the Earth’s Crust
O
Si
Al
Fe
Ca
Na
K
Mg
Total
Weight %
46.60
27.72
8.13
5.00
3.63
2.83
2.59
2.09
Atom %
62.55
21.22
6.47
1.92
1.94
2.64
1.42
1.84
98.59
100.00
Ionic Radius Volume %
1.40
93.8
0.42
0.9
0.51
0.5
0.74
0.4
0.99
1.0
0.97
1.3
1.33
1.8
0.66
0.3
100.00
Most common silicates are from these
O alone = 94 vol. % of crust
Perhaps useful to think of the crust as a packed O array with interspersed
metal cations in the interstices!
Analogy works for minerals too (they make up the crust)
Chemistry Review
Bohr model for the atom
1. Nucleus = p + n.
“element”)
Beryllium 1s2 2s2
(#protons = Atomic # identifies
(nucleus ~ all mass) Nucleus gives elements their properties
p + n (variable)  atomic weight (isotopes)
At. Wt. is real # due to average of isotopes
2. Electrons e- spin around atom and give it its’ size
Atomic radii in the range 0.5-2.5 Å (1 ångström = 1×10−10 m)
e- in special shells w/ particular energy levels- quantized
The Atom
Hydrogen
The Bohr Model
Nucleus
Hydrogen
The Schrödinger Model
- contains most of the weight (mass) of the atom
- composed of positively charge particles (protons) and neutrally
charged particles (neutrons)
Electron Shell
- insignificant mass
- occupies space around the nucleus defining atomic radius
- controls chemical bonding behavior of atoms
Electrons are in shells.
Octet Rule (Sienko & Plane p 55:
When atoms combine, the bonds formed are such that each atom is surrounded by 8 e-
s orbitals have up to 2 e-
p orbitals have up to 6 e-
s - orbitals
2. The s orbitals fill a shell
first, then the p-orbitals.
d-orbitals have up to 10 e-
p-orbitals
1. Within each shell, electrons
move in orbitals, volumes
where an electron is most
probably located.
First they occupy separate
sub-orbitals, then when all
of Nesse are occupied they pair.
Electrons
occupy orbitals in order of energy
level
Cl =1s22s22p63s23p5 =17 eNotice 4s fills
before 3d because
4s has a lower
energy
Filling up the
Orbitals
Order controlled by the
energy of the orbitals
also 5s fills before 4d
Problem 1
a. What is the electron configuration of a
neutral atom of Calcium, element 20:
Answer: Ca = 1s2 2s2 2p6 3s2 3p6 4s2

b. What is the electron configuration of a
neutral atom of Aluminum, element 13
Answer: Al = 1s2 2s2 2p6 3s2 3p1
Beyond Calcium, d-orbitals fill in complex ways, in order of orbital energy.
C. The order of increasing energy is
1s 2s 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f Nesse p.41
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Characteristics of an atom depend a lot on electron
configuration

Atoms with a different numbers of protons &
electrons, but with similar electron
configurations, have similar properties

This is especially true for the outermost shell
 Periodic Table
Structure of the Periodic Table
# of Electrons in Outermost Shell
Noble
Gases
metals
Anions
--------------------Transition Metals------------------
NOTE : Primary Shell being filled
Column number gives electrons in outermost shell; predicts Ion valence
It is the outermost shell or valence electrons that
predicts bonding behavior
Similar outermost shell configurations  Groups in
the Periodic Table columns
alkali metals (I) have one e- in outer shell
halogens
(VII) have 7 einert gases (VIII) have 8e- ... filled s & p
Problem 2
A neutral atom of Calcium has the
electronic configuration of:
1s2 2s2 2p6 3s2 3p6 4s2
 Question: Which are the valence
electrons?
 Answer: the 4s2. The Calcium can lose
these rather easily, yielding a Ca++ ion.

Atoms of Geologic Importance
Important elements are abundant
Elements and Isotopes
Elements are defined by the number of protons
in the nucleus (atomic number).
 In a stable element (zero charge), the number
of electrons is equal to the number of protons
 The various isotopes of a particular element are
defined by the total number of neutrons in
addition to the number of protons in the nucleus
(isotopic number).
 Various elements can have multiple (2-38)
stable isotopes, some of which are unstable
(radioactive)
 Isotopes of a particular element have the same
chemical properties, but different masses.

Ions and Valence States
Elements can attain an inert gas configuration (octet rule)
Cations – “positive ion” one or more electrons
removed from outer shell, often a metal, e.g.
Na+, Fe++, Fe+++, Mg++, Ca++, S+6
Anions – “negative ion” one or more electrons
added to outer shell; always a non-metal
element, example Cl-, S-Valence State (or oxidation state) – the common
ionic configurations of a particular element determined by how many electrons are typically
stripped or added to form an ion
Valence States of Ions and Anionic
Groups common to Rock-forming
Minerals
Cations – metals,
+1 +2
+3 +4 +5 +6 +7
-2 -1
-----------------Transition Metals---------------
transition metals,
semiconductors and
nonmetals that have
lost electrons
Anions – nonmetals
with extra electrons
Anionic Groups
tightly bound ionic
complexes with
net negative
charge, SO4-2,
CO3-2, NO3-, SiO4-4,
PO4-3
Problem 3
A neutral atom of Calcium has the
electronic configuration of:
1s2 2s2 2p6 3s2 3p6 4s2
 a. What is the electron configuration for
the Ca++ ion?


b. How many electrons does Ca++ have in
its outermost shell?
 Alkalis
have one extra electron, can
lose it to attain outer octet. This results in
an ion with a +1 valence, Na+
II alkaline earths will lose 2 e- 
+2 Become a +2 valence ion, Ca++
 Group
will capture an e-  inert gas
configuration.  -1 valence ion. Cl-
 Halogens
Properties derived from outer eIonization potential  energy required to
remove the least tightly bound electron
 Electron affinity  energy given up as an
electron is added to an element
 Electronegativity  quantifies the
tendency of an element to attract a shared
electron when bonded to another element.


In general, first ionization potential, electron
affinity, and electronegativities increase from left
to right across the periodic table, and to a lesser
degree from bottom to top.
Ionic vs. Covalent
Elements on the right and top of the periodic
table draw electrons strongly
 Bonds between atoms from opposite ends
more ionic, diatomics are 100% covalent
 Bond strength  Covalent>Ionic>metallic
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Affects hardness, melting T, solubility
Bond type affects geometry of how ions are
arranged

More ionic vs. covalent = higher symmetry
Atomic Radius

A function partly of shielding, size is critical
in thinking about substitution of ions,
diffusion, and in coordination numbers
Again: Outer Electron stuff
Ionization Potential – measure of the
energy necessary to strip an element
of its outermost electron. Low in alkali
metals, e.g. Sodium Na => Na+
Electronegativity – measure strength
with which a nucleus attracts
electrons to its outer shell. High in the
abundant element oxygen.
Electronegativity (e-neg)
Metals w/ e-neg < 1.9 thus lose e- and  cations
Nonmetals
> 2.1 thus gain e- and  anions
Metalloids intermediate (B, Si, Ge, As, Sb, Te, Po)
Small Cations
(Oxide Ion)
Ferric Ion
Medium Cations
Note Sizes
Huge K+ needs
a large space
between anions
Ferrous Ion
Large Cations
Huge Cation
1.Cations are smaller than their
neutral counterpart. Electrons
lost, so outer electron cloud is
smaller.
2.Anions are much larger than
their neutral counterpart.
Electrons gained, so outer
electron cloud is larger.
Problem 4
Write down the common cations of Silicon
Si, Aluminum Al, Iron Fe (there are two,
ferrous and ferric Iron), Magnesium Mg,
Sodium Na, Calcium Ca, Potassium K,
and Sulfur.
 Write down the common anions of
Oxygen, Chlorine, and Sulfur.

The sizes vary with Coordination,
the number of touching neighbors
Unit Cell
The Cations fill the space available between the Anions
Next Lecture
Bonding and Ionic Radii