• Define an isotope, isotone and isobar and give an example of each

Isotopes are atoms with the same number of protons, but a different number of neutrons - e.g 16O Isotones are atoms with the same number of neutrons, but a different number of protons - e.g 37Cl Isobars are different elements with the same mass number - e.g 40Ar, 40K, 40Ca

• Describe the changes that occur during beta decay.

An unstable atomic nucleus has too many neutrons and so undergoes decay as it does not like to be radioactive, it prefers to be stable. In doing so, a new element is formed. b-decay of a neutron transforms into a proton by emission of an electron (neutron -> proton + electron) • What applications use beta capture? It is often used for dating of minerals

• Give the equation for 14C going through beta -decay. C-14 → N-14 + β–

• What evidence is there that the universe is expanding?

Evidence for the expansion of the universe is from the observed red shift in the spectra of light reaching us from the stars in very distant galaxies.

• Explain what is meant by ‘red shift’.

The displacement of spectral lines towards longer wavelengths (the red end of the spectrum)

• Comment on the decreasing abundance of elements with increasing atomic number.

elements with even numbers of protons are more abundant than elements with odd atomic numbers (protons)

• Explain why Li, Be and B have very low abundances.

Because there are no stable nucleides of 5 or 8 so as soon as they form they decay. Because they don’t hang around, this is why we don’t have much Li, Be, or B. Instead, 3 particles are needed to combine - e.g two 1H with 4He to form 6Li This is tricky to do because This required three particles to be in the same place at the same time in the correct orientation

• Referring to the Hertzsprung-Russel diagram, describe the features of a red giant.

Red giants are extremely large (radius is very large, hence high luminosity) but lower temperature stars (because star's energy spreads across a larger area, so temperature is cooler)

• Discuss the chemical composition of the solar system.

The most abundant elements in the solar system are hydrogen and helium. As the atomic number increases, there is a general trend downwards in abundance that creates a saw-tooth like plot. This sawtooth pattern is because elements with even numbers of protons are more abundant than elements with odd atomic numbers (protons).

• Explain why iron has a much higher abundance in the solar system than expected.

Because it is a low volatile element and was captured so is abundant today. Most stable element and is the end point of fusion in the stars.

• Describe how elements are produced in stars by nucleosynthesis.

Protons and neutrons combined, rapid expansion occurred, temperature and density fell, and this left us with light elements. The vast abundance of these elements were hydrogen and helium. In the cores of stars, nuclear fusion occurs due to very high temperatures and pressures So as clouds of He and H are pulled together, the gravitational energy is converted into heat. This is important because the hotter an atom is, the faster it moves, and nuclei need to move fast in order to interact with each other. the Positively charged nuclei are forced together (overcoming Coulomb barrier, such that the strong nuclear force overcomes electrostatic repulsion force) Most stars are converting hydrogen into helium, but in order for other elements to be formed, other processes must also be occurring.

• Explain what a first generation star is and how it is formed.

A first-generation star is a star made from the elements of the big bang - primarily hydrogen and helium. Two hydrogen atoms have enough energy that come together to form deuterium (heavy hydrogen) Deuterium can then form with another hydrogen to form free helium This process is happening all around So then two heliums can come together to give the stable 4He. During this reaction, two hydrogens are released, and these guys can then go back to the beginning of the cycle to create more helium This process occurs at high temperature. When the central temperature of a star reaches about 10^7 K, protons in the H/He mixture are in sufficiently rapid motion for fusion to occur.

The collapse of the star is stopped by the internal pressure created by the escaping heat produced by the formation of helium from hydrogen He nuclei build up in the core of the star, but do not interact with each other at 107 K (it is not hot enough or dense enough). This causes the star to build up a source of He This process happens faster in large stars, so Large stars will exhaust their H fuel supply faster than smaller stars. As all the H is consumed, the star loses the ability to hold gravity back and starts to contract. It becomes smaller and denser. As it does that, the pressure increases and the temperature of the core rises to 10^8 K. This rise of temperature allows for He fusion to begin (He nuclei have 2 protons hence a 2+ charge, so are harder to fuse compared to H nuclei with 1+ charge) 2 helium atoms come together to form Be, but because it has a mass number of 8 it is highly unstable and usually decay. However, sometimes they hang around long enough to attach to another helium to form carbon in its excited state (it then releases some energy to form back into its stable state) That energy is released because the mass of carbon is less than 3He, and energy appears as heat This reaction can then be followed by successive a-particle fusion processes, with further core contractions and temperature increases This is a cycle which builds up carbon stores so when helium runs the star contracts and we burn carbon and so contract and heat and burn fuel

• How are elements redistributed in space?

Synthesised elements are held within the star but they need an escape mechanism. The elements synthesised in the core of a star may be distributed back into space as interstellar dust and gas by: • mass loss from giant stars (solar flare, eruption) • supernova explosions This allows second (and subsequent) generation stars to start with more than H. They have formed with the heavier nuclei that have formed at the end of the first generation star's life. The important consequence of this is that subsequent stars begin their lives containing small amounts of the heavier elements N, C, and elements up to Fe.

• Describe the s and r processes. Compare and contrast these processes. This neutron capture process can happen in two ways: Slow (s) process and rapid (r) process

Slow process (s-process) The s process is a slow, controlled build up of elements The neutrons are spaced out and the new nuclides they have a change to undergo b-decay before the next neutron impact and so the nuclei follow predictable patterns

Iron 56 - gradually increase the number of protons in the nucleus - go from iron 56 to 57 to 58 until we hit an unstable isotope (iron 59) and then it will DECAY (so remember the neutron converts into a proton) which converts into cobalt Now we have cobalt will take a neutron and move up to its unstable form and then that will undergo decay This goes on and on until bismuth (last stable atom) The s process occurs concurrently with the production of Fe in the core, and in a controlled manner; analogous to a nuclear reactor New nuclides have chance to undergo -decay before the next neutron impact, and the nuclei follow the pattern of stability shown earlier The s-process stops at bismuth, the heaviest ‘stable’ isotope; elements heavier than Bi are all radioactive and must be produced by rapid processes in supernovae This process produces most of our stable nuclides

R process The rapid process involves an intense bombardment of neutrons In a supernova explosion iron/ an atomic nucleus is hit with neutrons until the nucleus cannot absorb any more. At this point, the neutrons begin to pass through. The elements is unable to decay to a stable isotope during this time because a neutron will constantly jump in when it undergoes decay This process allows the formation of radioactive isotopes Once the bombardment stops, The neutrons disappear and the neutron rich isotopes can undergo radioactive decay until the element reaches a stable neutron to proton ratio. Although a rapid process, the decay process can still take a long time - e.g half life of uranium is exceptionally long which allows us to date things

Comparing the two processes: the s process is steady, the r process is more rapid

• What evidence is there for stellar nucleosynthesis?

1. Energy - Only nuclear fusion would provide sufficient energy to keep stars burning. Temperature and pressure are high enough to allow fusion of elements

2. Solar Neutrinos - Produced during conversion of H to He. A burst of neutrinos was observed during formation of SN1987A They interact weakly with matter

3. We have observed stars going supernova and the spectral lines observed during this event gave the spectral lines for Tc, and there is none of this on earth. Therefore, the only way we could have got this element is from stellar nucleosynthesis

• Discuss the evidence that suggests that the planets were formed from the sun.

1.All planets are spinning in the same direction as the sun 2.The orbit of each planet around the sun is almost circular and they all lie in nearly the same plane (corresponding to the sun’s equator). 3.Even spacing between planets (increase is 1.6 x). This works fine until we get to the space between mars and jupiter but then we have the asteroid belt and think that there was a failed planet in that space.

• Discuss the important features of the planets in the solar system, including any trends.

Terrestrial planets have high densities and giant planets have low densities There is a large range of radius with no trend and same with mass

• What is ‘corrected density’ and why is it used?

What is corrected density and why is it required = the density of the planet without the influence of gravity - important because larger planets have a larger gravitational pull so we want to correct those factors out to know the density without the effect of gravity

• What are the main differences between the terrestrial and giant plants? Why have these differences arisen?

Density

• Why do the inner planets have a higher density than outer planets?

Early in the formation of the solar system, ions produced by the Sun removed Highly volatile elements from the inner solar system and were mainly lost as gases to the outer solar system, leaving dust particles and heavy elements (less volatile) behind, which subsequently condensed to form the terrestrial planets

Oxygen - Fate 2 (Moderately volatile) Attracted to compounds with H, but more strongly attracted to form bonds with metals to form highly involatile oxide materials. So it sticks around In the first 10 elements, O is the only element sufficiently abundant and prone to form solid phases. However there were 5x more oxygen atoms than metal atoms, so only 20% of O could form compounds with metals. So the remaining 80% joins with H and is lost

• What information can density give us about planets? What assumptions do we have to make?

Density gives us a clue about the chemical composition of the planet but is a rough approximation. One of the main assumptions we make is the heavier the element, the greater the density