end of term test Flashcards
what is the doppler effect
change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source
describe the red shift
the absorption lines of distant galaxies are more shifted towards the red end of the spectrum
distant galaxies are moving away faster than nearby ones
why does cosmic microwave background radiation now appear cooler (4000K to 3K)
universal expansion
which 2 elements were found during the big bang and shortly after
H(90%)
He(10%)
describe nucleosynthesis
-Hydrogen and helium fusion in 1st generation stars and their subsequent supernovae created some heavier elements including C.
-2nd and third generation stars achieve H fusion via the CNO process.
-Elements up to 56Fe are made during the last stages of a stars life.
-The remaining heavy elements are produced by neutron and proton capture in supernovae.
summarise atomic theory
-Atomic theory grew out of the discovery of subatomic particles such as the electron, in 1897 by J.J. Thomson.
-In the Bohr-Rutherford model (1913), the atom consists of a tiny, positively charged, heavy nucleus circled by negatively charged, light electrons
-The atomic model was then improved by quantum mechanics (Heisenberg and Schrödinger, 1926).
-the nucleus is small and dense, whereas the light, electron cloud is vast.
valency
a measure of its combining power with other atoms when it forms chemical compounds or molecules. Valence is equal to the number of bonds that an element can form and is determined by the number of electrons which need to be exchanged in order to reach a more stable configuration.
Molecules
two or more atoms
chemical compounds
two or more different types of elements
oxidation state
the number of electrons that an atom can ‘lose’ in a chemical compound
redox
Oxidation is loss of electrons and reduction is gain of electrons.
mole
the amount (in grams) of 6.022 x 1023 atoms (or molecules) of that substance.
main ideas of quantum theory
-Energy can be transferred between -entities only in discrete ‘packets’, not as a smooth spectrum.
-Tiny entities (fundamental particles) have the properties of both particles and waves, depending on how they are observed.
what are metals
Metals are elements that need to lose electrons in order to reach a more stable electronic structure.
Electronegativity
measure of the ability of an atom in a molecule to attract electrons to itself.
First ionisation potential
energy required to remove one electron completely from a neutral atom (in a vacuum).
Standard electrode potential
voltage generated when one mole of electrons is removed from one mole of an element or ion “in the standard state”
mineral
a naturally occurring solid with a specific composition and a distinctive internal crystal structure
they have a combination of ionic and covalent bonding
nesosilicates
Isolated tetrahedra joined together by cations
e.g. olivine, garnet
inosilicates
single and double chained e.g. pyroxenes and amphiboles
sorosilicates
2-6 tetrahedra forming isolated anions, joined together by cations.
e.g. epidote
cyclosilicates
Ring or double rings of tetrahedra, joined together by cations.
e.g tourmaline and beryl
phyllosilicates
Sheets of tetrahedra, joined together by cations.
Unshared oxygen bond to cations between two layers, but connection with other layers is weak.
e.g. biotite and muscovite
tectosilicates
3D framework of tetrahedra with a 1:2 Si:O ratio (makes up 75% of Earth’s crust!).
Al3+ can replace Si4+ in the feldspars, but not in quartz.
e.g. zeolites, feldspars and quartz
why are silicates versatile
the ability of unpaired electrons on oxygen to form ionic or covalent bonds with metals or other silicate tetrahedra.
what is element compatibility
a measure of how well it fits into a given crystal lattice.
Refractory elements and compounds
high melting points
e.g. silicates and lots of metals
Volatile elements
low melting points, and are often found as liquid or gas
e.g. common gases, some metals (Pb) and metalloids (e.g. S, unless bonded with Fe)
How do we know Earth’s composition?
Direct measurements
Density and Seismology
Atmophile
volatile gases: Ar, H2O, CO2, N
Lithophile
prefer silicate rocks: Si, O, C, Al, Ti
Chalcophile
sulphur loving: Pb, Cu, Zn, Pt, As
Siderophile
iron loving: Ni, Au, Ag, Cu, Pt
Core Formation
-Mix of condensates form proto-planet which then separates by gravity.
-Much of the Earth must have been molten.
-Silicate and Fe-metal fluids are immiscible (they don’t mix).
-Fe-metal denser than silicate, so would sink into the core.
-Heat provided by impacts and release of gravitational potential energy from the core formation.
Crust Formation
Partial melting
Solidus
Liquidus
Phase diagrams
Solid solution
distribution of refractory and volatile elements
Planets near the sun contain mostly Refractory elements. Planets further out also contain Volatile elements in great abundance
trace elements, minor elements and major elements
A trace element forms <100ppm of a crystal. Minor elements are 100ppm – 1 wt%. Major elements are > 1 wt%.
Radioactive isotopes
undergo radioactive decay into other elements/isotopes.
Radiogenic isotopes
isotopes resulting from the decay of other isotopes.
which istope is radioactive and radiogenic
3H (tritium)
Stable isotopes
do not decay, but they may be radiogenic
Alpha decay
Loss of alpha particle (He atom 4/2He)
Proton number reduce by 2, mass number by 4.
Beta- and Beta+ decay
Loss of beta particle (electron (β-) or positron (β+)). Proton number increase/decrease by 1, mass number stays the same
Nuclear fission
Irregular break-up of atoms
decay equation
𝑑𝑁/𝑑𝑡=−λ𝑁
𝑁= 𝑁_0 𝑒^(−λ𝑡)
what is decay used for
to work out ages of Earth materials and to study the different sources of Earth materials.
fractionation
Light stable isotopic ratios may be altered during physical or chemical processes.
what does fractionation depend on
Usually mass dependent, because light isotopes react faster (kinetic) and heavy isotopes form more stable bonds in solids and liquids, compared to liquids and gases respectively.
Le Chatelier’s Principle
When a system is disturbed, equilibrium is re-established by opposing that disturbance.
Chemical equilibrium
the state where the rate of the forward reaction is equal to the rate of the reverse reaction
depends on the concentration of the reactants, as well as temperature and pressure
equilibrium constant equation
𝑷𝒓𝒐𝒅𝒖𝒄𝒕𝒔/𝑹𝒆𝒂𝒄𝒕𝒂𝒏𝒕𝒔
if K < 1, then the backward reaction is favoured and we will have more reactants at equilibrium.
what is a saturated solution
A solution is saturated with respect a compound if the dissolved concentrations of its components are at equilibrium with the solid compound
Factors influencing solubility
Ionic shielding
e.g. Polymorphism, e.g. calcite and aragonite
Grain-size
Complexation, e.g. BaSO4 or MgSO4 or BaCO3 etc.
Temperature, pressure and pH
acidity
determined by the activity of protons (H+ ions) in that solution.
acid and base
an acid is a compound that donates hydrogen ions when dissolved in water. A base accepts hydrogen ions.
colloids
suspensions of tiny particles.
Colloids include gels and emulsions; the particles do not settle, and cannot be separated out by ordinary filtering or centrifuging like those in a suspension, but they can be separated.
properties of water
The universal solvent:
Water can dissolve almost
any ionic mineral/crystal/
molecule as well as many
gases.
Transparent: allows light
through
Cohesive
Temperature regulator: high heat capacity
Dense when liquid and less dense when solid: i.e. ice floats
shape of water
-bent shape
-angle between the bonds is 104.5
polar water
Water’s polar nature means that it can dissolve many substances, making it useful for transporting salts etc that are needed for life.
high heat capacity
Polarity also results in hydrogen bonds, which help give water a high heat capacity. High heat capacity leads to stable living environments and helps regulate body temperature.
Thermodynamics
a body of science that deals with how energy is exchanged between systems.
open, closed and isolated system
The system is open if matter can move across the boundary.
The system is closed if matter cannot move across the boundary.
If the boundary also prevents energy moving through it, the system is isolated.
intensive and extensive properties of a system
Intensive properties are independent of the amount of mass that is present (e.g. temperature, pressure, density). i.e. these can vary without varying the mass.
Extensive properties are mass and volume. These depend a lot on the mass
phase
‘a uniform, homogeneous, physically distinct and mechanically separable portion of a system.’
Components
the chemical constituents by which the phases are made up
Gibb’s Phase Rule
The Gibb’s phase rule relates the number of components (c), the number of phases (p), and the degrees of freedom in a chemical system.
p + f = c + 2
Generally in chemistry, if the number of components equals the number of phases, we have two degrees of freedom which are Temperature and Pressure.
enthalpy
In a chemical reaction, the energy contained within all the different bonds between elements
enthalpy of formation
the heat absorbed or given off by the reactions in which the compounds, ions or molecules are formed from the elements.
The First Law
The increase in internal energy of a system is the heat that flows across the boundary from the surroundings minus the work done by the system.
hess’s law
ΔH˚r = heat (enthalpy) of reaction = ΔH˚f (products) - ΔH˚f (reactants)
Entropy
ΔS, is a measure of the orderliness of energy, or the randomness of the energy in a system.
entropy equation
ΔG˚r = ΔH˚r - TΔS˚r
Reactions tend to go forwards if ΔH˚r is negative (exothermic) and entropy increases as a result of the reaction, because then energy is dispersed from the system to its surroundings.
Gibbs Free Energy
ΔG˚r = ΔG˚f (products) - ΔG˚f (reactants)
oxidising agents
compounds that are acidic (proton donors and electron)
Redox potential
the tendency of an environment to receive or supply electrons.
pe = -log[e-]
photosynthesis and respiration
CO2 + H2O + energy = CH2O + O2
CH2O + O2 = CO2 + H2O + energy
