Sci 10

• Nucleosynthesis


  The process of the formation of the elements
• Element


  Fundamental component of matter; cannot be decomposed into simpler substances by ordinary chemical processes
• Typical representation of an atom and its parts
• Atom


  Subunits of elements composed of a nucleus surrounded by electrons
• Electron


  Negatively-charged subatomic particle
• Proton


  Positively-charged subatomic particle
• Nucleus


  Composed of protons and neutrons; found at the center of the atom
• Neutron


  Neutral subatomic particle
• Three main settings where nucleosynthesis occurs

  • Big bang
  • Stars
  • Supernovae
• Big Bang nucleosynthesis


  1. Resulted in the formation of the lightest elements

  2. All hydrogen (1H or proton and some 2H or deuterium)

  3. Most helium (4He and some 3He)

  4. Traces of lithium (7Li)

  5. Within the first three minutes after the Big Bang

  6. Via fusion reactions combining lighter nuclei into heavier nuclei

  7. Energy in the form of electromagnetic radiation is released
• Formation of heavier elements up to iron occur in stars via stellar nucleosynthesis


  1. From He up to iron (Fe) within the core (interior) of stars via nuclear fusion

  2. Hundreds of millions of years after the Big Bang

  3. Diffuse clouds of H and He initially formed compact structures

  4. Great amount of gravitational energy was converted to heat

  5. Heat produced starts a "nuclear fire" causing the nuclei to collide and form heavier nuclei

  6. Energy is subsequently released, which powers the star

  7. Series of fuel burning processes with increasing ignition energy requirements occur

  8. Hydrogen burning: Collision of 1H nuclei form 4He

  9. Star cools and collapses once H is used up

  10. Heat released causes the core temperature to rise again

  11. If the ignition temperature for He is reached, He burning follows

  12. Helium burning: Collision of two 4He forms 8Be (beryllium-8)

  13. Collision between 8Be and another 4He forms 12C (carbon-12)

  14. Collision between 12C and another 4He forms 16O (oxygen-16)

  15. Process stops for "intermediate-mass" stars: Temperature not high enough for C burning, Star becomes white dwarf

  16. Cycles of further fuel depletion, collapse, core temperature rise, and ignition of heavier fuel can continue for massive stars (more than 8 times heavier than the sun)

  17. Element formation stops at 56Fe (iron-56): Stable nuclei with after iron have masses greater than the masses of the nuclei that are fused, Subsequent nuclei formation can no longer release energy but will instead require the input of energy
• Supernova nucleosynthesis generates elements heavier than iron

  1. Up to uranium (U)

  2. Supernova: Explosion upon the death of massive stars triggered by the collapse of iron core, Explosion produces enough energy needed for further fusion reactions

  3. Neutron capture: During an explosion, free neutrons are produced, which can be captured by existing nuclei, 56Fe nuclei become heavier as more neutrons are captured

  4. Beta (β) decay: converting neutrons to protons and electrons, e.g., conversion of one neutron from 57Fe creates a 57Co (cobalt) atom

  5. Nuclear fission: fragmentation of heavy nuclei into lighter ones

  6. Supernova remnants disperse into space, enriching the surrounding interstellar medium with newly synthesized elements, These elements become incorporated into successive generations of stars, planets, and other astronomical bodies, resulting in the diversity of elemental compositions observed in the universe
• Atomic number (Z)


  Number of protons
• Mass number (A)


  Number of protons + neutrons
• Isotope


  Atom of the same element that has the same number of protons but a different number of neutrons, i.e., different A
• Abundance


  Measure of how relatively common an element is, usually by comparison to the amount of another element, Measured by spectroscopic techniques and hi-resolution imaging or direct analysis of samples from solar system
• Abundances among objects in solar system and stars vary widely, Overall, the elemental composition of the universe is uniform
• Hydrogen is the most abundant, making up ~88.6% (by number) or ~73% (by mass) of all atoms or in the universe, Helium is second with ~11.6% (by number) or ~25% (by mass), H and He make up ~99.9% of all elements and ~99% of the mass of the universe
• Nuclear stability


  Ability of an element to retain its current nuclear state within a certain time interval
• Binding energy


  Energy required to separate the protons and neutrons within a nucleus; higher binding energy corresponds to greater stability
• Radioactive decay


  Spontaneous decomposition of an unstable nuclei to a more stable one by emitting energy or particles
• Half-life


  Measure of stability of unstable nuclei; the amount of time it takes for half of a substance to disintegrate
• Belt of stability


  Plot of relative amounts of protons and neutrons that give stable nuclei
• Nuclei with even numbers of protons, neutrons, or both are more likely to be stable, Nuclei with "magic numbers" of nucleons (2, 8, 20, 28, 50, 82, and 126) are stable against nuclear decay, "Double magic" - nuclei with magic numbers of both protons and neutrons
• Valence shell


  Outermost shell containing valence electrons; electrons can be added or removed from this shell during chemical reactions
• Electron charge


  Negative, one unit mass: 1/1800 of proton or neutron
• Neutron charge


  Neutral mass: 1 unit
• Proton charge


  Positive, one unit mass: 1 unit
• Net charge


  Sum of the charges
• Mass


  Sum of the masses (≈sum of protons & neutrons)
• Bohr models show the structure of the six most common atoms found in living systems, electrons orbit the nucleus in shells like planets orbiting the Sun
• Electron orbital


  Indicates the volume of space in which a particular electron is likely to be found 90% of the time
• p orbital


  Dumbbell-shaped; 3 types
• Elements are arranged in the Periodic Table according to electronic structure
• Elements in same vertical column (group)


  Have similar chemical characteristics because they have the same number of electrons in their valence shell
• Elements in same horizontal row (period)

  Have the same highest electron energy level
• Ionization Energy (IE) or Ionization Potential


  The minimum energy needed to remove the outermost electron from the neutral atom in the gaseous state, generally decreases down a group and increases across a period
• Electronegativity (EN)


  The measure of the ability of an atom in a chemical compound to attract electrons from another atom in a compound, generally decreases down a group & increases across a period (exceptions: noble gasses, lanthanides, and actinides)
• Metallic Property


  The tendency of an atom to lose electrons during chemical combination, increases down a group and decreases across a period
• Nonmetallic Property


  The tendency of an atom to gain electrons during chemical combination, decreases down a group and increases across a period