Midterm 1 - Elements & Nuclides Flashcards
What is geochemistry?
The use of chemistry to understand the earth and how it works, including the solid earth, natural waters, and atmosphere. Can be applied to aspects of either natural or anthropogenic processes.
What do geochemist study?
formation and differentiation of planets, mantel convection, origin of granite and basalt, mineral deposits, lithification, metamorphism, changes of oceans, etc.
What is the two traditionally geochemistry sub-fields?
Low temperature and high temperature.
Structure of the Earth - Core
~3,500 km thick
extends about 1/2 way to the surface
~about 1/3 of the mass of the earth
FE-Ni alloy
inner solid and outer is liquid.
Structure of the Earth - Mantle
~2900 km thick
~2/3 of the mass of the earth
mostly ultramafic (olivine and pyroxene dominated)
Structure of the Earth - Crust
<100 km thick
~0.5% of the mass of the earth
continental vs.oceanic
Structure of the Earth - Continental crust
typically ~35-40km thick
relatively permanent
felsic (feldspar dominated)
Structure of the Earth - Oceanic Crust
typically <6km thick
<200 Myr old
Magic (sub-equal amount of olivine, pyroxene, and feldspar)
Energy drive geological processes - solar energy
Hydrologic cycle: solar energy drives atmospheric and oceanic circulation, thus the hydrologic cycle.
Water vapor in the atmosphere precipitates on the land as rain/snow, percolated as surface/ground water into the ocean.
Streams and oceans evaporated into atmosphere
Energy drive geological processes - earths internal heat
Tectonic Processes: the gravitational potential energy released during the formation of the earth (accretion of planetesimals and core segregation) and head from radioactive decay of U,Th, and K drives tectonic processes such as convection into the outer core and mantle. This leads to plate tectonics.
Outermost part of Earth is cool nigh to be rigid, which is the?
lithosphere
**
how the studying going?
Mantle below the lithosphere is hot enough to flow slowly under stress is
the asthenosphere
convection flow of the asthenosphere drives?
the motions of the lithospheric plates, which cause most geological action (earthquakes, volcanism, and metamorphism)
Other examples of the convection flow of the asthenosphere are?
mantle convection, subduction, and arc volcanism.
how do geochemists study the earth?
using analytical data like
1. major and trace element concentration.
2. isotopic rations
3. elements in solutions, mineral phases, or organic matter.
Bulk Silicate Earth (BSE) includes what elements?
44% O
21% Si
2.5% Ca
23% Mg
6.2% Fe
2.4% Al
Trace elements not stoichiometric constituents of phases in the system of interest are?
Rb, Sr, Sm Nd, Th, U, and Pb
Bulk Earth (including the core)
O=32
Fe=32
Mg=15
Si=14
Ni=1.8
Ca=1.7
Al=1.6
most of the Fe and Ni is located in the core.
What is an Earth Reservoir and what is it used for?
Used to better understand the origin and evolution of our plant.
Can be real (upper mantle, core, atmosphere) or hypothetical (BSE).
What are the compositional differences between the reservoirs?
C1 chondrites: type of primitive meteorite that is though to be compositionally similar to the building blocks of the earth
Continental Crust: a bulk average estimate
Primitive mantle: the composition of the earthʻs mantle right after core information, but before the differentiation of the mantle or formation of the crust.
What were the steps and calculations done for the earth reservoirs google sheet.
review google sheet and question answers
elements are composed of?
subatomic nucleons.
positively charged protons and neutral neutrons orbited by negatively charged electrons.
atomic number?
Z = # of protons in the nucleus of an atom
atomic number determines?
the number of electrons in a neutrally charged atom
Example of Helium
z= 2
charge = # protons - # neutrons
2-2=0 (neutral)
neutron numer
n = number of neutrons in the nucleus
ions form?
when an atom gains electrons to form negatively charged anions or loses electrons to form positively charged cations
mass of proton and neutron are?
similar
mass of a proton or neutron is
1836x greater than an electron.
mass number
A = z + n
aka number of protons + number of neutrons
Isotopes =
same Z but different N and A
remember z = protons
N = neutrons
A = mass number
do same element different mass
Isobars =
different z and N but same A. different element same mass
atomic mass unit, abundance, and weight
amu
relative proportion of the naturally occurring isotopes
sum of the masses
so atomic weight = mass of element * abundance. added together = amu
DO SOME PRACTICE ONES - ON SLIDES
Radioactive decay is a process?
in which a nucleus undergoes a spontaneous transformation into one or more different nuclei and simultaneously emits radiation, loses electrons, or undergoes fission.
what is radioactivity?
property of the nucleus. it is independent of the number of electrons, and thus, any physical or chemical environment of the atom (mineral or fluid host, temperature, pressure, time,etc)
Radioactivity is a property?
of the nucleus. It is independent of the number of electrons, and thus, any physical or chemical environment of the atom.
details about the chart of the nuclides?
black: naturally abundant nuclide
gray: naturally rare or artificial nuclide
yaxis: Z
axis: N
y=different elements
x= different isotopes of each element
valley of nuclear stability…
for heavier elements, N>Z
extra neutrons help to counteract the repulsive force between the positively charged protons.
unstable or radioactive isotopes…
most known nuclides decompose spontaneously until they reach a stable configuration.
most do not occur naturally because their decay rates are rapid compared to the age of the solar system.
one of the most important elements in geochemistry is?
strontium…
isotope geochemists routinely use mass spectrometers to detect minute differences in the atomic weight of Sr separated from geological materials, such as foraminifera or basaltic lavas.
Alpha Decay:
is spontaneously emitted from the nucleus
a different element is left behind with Z-2, N-2, and A-4
most common at high mass numbers
Beta(Negatron) Decay
a neutron in the nucleus is transformed into a proton and electron
the electron is expelled from the nucleus
an isobar of a different elements is left behind (Z+1, N-1, A constant)
Occurs in N>Z
Positron Decay
A proton in the nucleus is transformed into a neutron and positron
the positron is expelled from the nucleus
an isobar of a different element is left being (Z-1, N+1, A constant)
Occurs if N<Z.
unusual for natural nuclides
Electron Capture
an extranuclear electron is captured by a proton in the nucleus, which is transformed into a neutron
an isobar of a different element is left behind
Branched Decay
a nuclide that is unstable (radioactive) with respect to more than one decay mechanism. the probabilities of decay by each process are additive.
Spontaneous Nuclear Fission
a relatively massive nucleus splits into smaller nuclei with the simultaneous release of energy
practice how to do the Decay Series!!
On SLIDES
the chemical properties of an…
element are determined by the way its outermost, loosely bund electrons interacts with other elements to form chemical bonds
the electronic structure of an atom and the number of its outermost, loosely bound electrons is controlled by…
quantum mechanic. this also controls the order of the elements in the periodic table
can understand the geochemical behavior of the elements based on their electronic structure.
three quantum numbers determine?
the organization of electrons into shells and orbitals.
n: the principal quantum number, the word shell is used t refer to all orbits with the same value of n because each increasing value of n defines a layer of electron density that lies further from the nucleus
I: shape of the orbitals (s,p,d,f)
m: the orientation of the orbital
the fourth quantum number determines the electronʻs spin… s:+1/2 or -1/2
Pauliʻs exclusion principle
no two electrons in an atom may have the same values of all four quantum numbers
electronegativity is?
a unit-less quantity that describes the tendency of an element to attract a shared electron when bonded to another element. Increases across the periodic table from left to right and bottom to top.
PRACTICE!!!!!
Types of Bonding are?
Ionic: total transfer of electrons from one atom to another. difference in electronegativity
covalent: atoms have a fair share of the electrons. difference in electronegativity.
what is a mineral?
a naturally occurring, inorganic solid with a defined chemical composition and a characteristic crystalline structure.
the silica tetrahedron is?
the building block of the silicate minerals
where the O-Si-O bonds are strongly covalent
it may polymerize to form a variety of structure by sharing O2
other metal elements fit into and modify the framework.
Isolated tetrahedra silicates
such as olivine and garnet
single chain silicates
such as pyroxenes, orthopyroxene and clinopyroxenes
double chain silicates
such as amphiboles
sheet silicates
such as micas and clay minerals.
framework silicates
such as quartz and felspars
The key controls on substitution are?
ionic charge and ionic radius. two ions must have a similar charge and size in order to substitute easily for one another.
the chemical properties of an element are determined by….
elements in the same…. or group of the PT have a similar….
thus their…. is similar and leads to the periodic chemical properties of the elements.
number of electrons
same column, similar configuration of outermost electrons
chemical behavior is similar
Ionic Radius is?
the effective size of an ion (bond length of an atom that is bonded to one or more other atoms).
is determined by the outermost electrons (just like bonding)
shielding is?
the electrostatic attraction of the outer electrons by the nucleus that is reduced by the cloud of the inner electrons.
the lanthanide contraction results from?
increasingly inefficient shielding.
as the atomic number increases from La to Lu, the positive charged in the nucleus increases.
the iconic radii might be expected to remain content
f orbitals are large and diffuse so not bale to shield nucleus
effective nuclear charge felt by the outermost electron increases and the ionic radius decreases.
Cations (+) have?
smaller ionic radii than anions
Ionic radii increase?
down the rows of the periodic table increases
ionic radii decreases?
across a row as charge increases
ionic radii decreases as atomic number?
increases for ions with the same charge
the large increase in ionic radii between?
column 10 and 11
goldschmidtʻs classification of the elements
atmophile elements are generally extremely volatile and are concentrated in the atmosphere and hydrosphere.
Lithophile elements?
readily form compounds with O2, and tend to be concentrated in the silicate portion of the earth (crust and mantle)
siderophile elements?
prefer to form metallic alloys, and tend to partition into a metallic liquid and are depleted in the silicate portion of the earth and concentrated in the earthʻs core.
chalcophile elements?
most easily form sulfides and are depleted in the silicate portion of the earth and maybe be concentrated in the earthʻs core.
large ion lithophile elements are
large ion, weak charge
high field strength elements are
small ion, strong charge
rare-earth elements
every element between La and Lu
noble metals or Pt group elements
Ru, Rh, Pd, Os, Ir, and Pt
Actinide elements include?
Ac, Th, Pa, U, and others that are no naturally occurring.
