Week 1: Chemistry of the Earth Flashcards
What is the atomic number?
number of protons
(fixed for each element- defines the element)
What about the number of electrons and neutrons?
number of electrons=number of protons in a neutral atom, variable number of electrons= chemistry
number of neutrons in nucleus can vary= isotopes
What is the atomic mass?
number of protons + neutrons
so this equals the mass of the nucleus
What elements did the Big Bang produce?
hydrogen (H) and Helium (He)
What occurs during hydrogen burning?
Hydrogen atoms combine to make helium
This is the main phase of a star’s lifetime
The sun is about halfway through this phase at the moment
Hydrogen atoms=protons
when two hydrogen atoms combine one proton breaks down into a neutron and a positron
3He is produced first then two 3He nuclei combine to make one 4He nucleus
What occurs during helium burning?
as a star evolves helium builds up in core
when hydrogen runs out the core contracts and heats up
this makes the envelope expand- Red Giant
helium nuclei begin to fuse together to produce 12C
What is the C-N-O cycle?
occurs in second generation stars that already contain 12C produced in older stars
successive nuclear reactions produce He form 4 hydrogen nuclei as well as 14N (other nuclei are not stable)
What does life and death of a star depend on?
its mass
stars like the sun end in a gently flowing wind of matter (planetary nebula) and eventually a white dwarf when burning ends= lifetime around 10 billion years
massive stars end in explosive events like supernovae= lifetime a few million years
What occurs in a supernovae?
Si burning produces 56Fe- end of fusion process
iron core undergoes gravitational collapse, leading to a supernova explosion
atoms in the expanding star are bombarded with neutrons leading to rapid neutron capture and build up of elements heavier than iron
as matter is ejected from a supernova, solid mineral grains condense from the gas
these grains are sprinkled into interstellar space
some become trapped in meteorites
What is the chart of nuclides? How does neutron capture affect this?
chart shows known isotopes:
-black squares are known isotopes
neutron capture= adding neutrons to an element increases the mass of the element until it is no longer a stable isotope
unstable nuclides created from neutron capture decay via eta-decay which moves the isotope up and left on the chart forming a new element. Beta decay= n -> p + e
slow (s) process of neutron capture = build up of nuclei heavier than 56Fe in second-generation stars
What occurred during the formation o the sun and the solar system?
1.collapse of a dense region of a molecular cloud
2.formation of a new protostar with a disk and bipolar jet outflows
3. protostar starts H burnign reactions and becomes a star (the Sun). Rock and ice material condenses in the disk and accretes to form planets, staellites, asteroids, comets etc
Chemical composition of the sun and solar system
determined from chondrite meteorites and the composition of the sun
Most abundant rock forming elements that make up the Earth= O, Mg, Si, Fe, S, Al, Ca, Na, Ni
Analysis/Interpretation of composition
composition makes sense when we know a little about nucleosynthesis
overall decrease in abundance with increasing atomic number
nuclei with even numbers of protons are more stable
