Formation of Elements

Formation of Elements

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Composition of the Universe:
92 elements
73% hydrogen
25% helium

2% others

2 types of Elements

1. Natural - through nuclear reaction
2. Synthetic - human technology

Hydrogen - oldest, most abundant, and lightest element
Uranium - heaviest natural element
Lithium - third lightest element

Big Bang Theory - explains how the elements initially formed which involves many chemical reactions including fusion, fission, and radioactive decay.

13.7 billion years old - age of the universe

Fusion - combines
Fission - separates

!! Larger stars have less life!!

4 Concepts of the Universe

  1. The Big Bang is an expansion of space
  2. As the universe expands, it cools
  3. The more energetic the particles are, the higher the temperature will be
  4. The identity of the element depends on how many protons it has

3 Cosmic Stages

  1. Big Bang Nucleosynthesis - formation of the light elements, hydrogen (H), helium (He), and lithium (Li)
  2. Stellar Evolution or Formation - formation of the heavy elements. from beryllium (Be) to iron (Fe)
  3. Stellar Explosion or Supernova - formation of elements heavier than iron (Fe).

Nucleosynthesis - the process that creates new atomic nucleus from preexisting nucleons, which is proton neutrons

Primordial or Big Bang Nucleosynthesis - process of producing the "light elements" shortly after Big Bang

Isotope - form of element that has the same atomic number of the original element but with different atomic mass or mass number

  • only 1 proton

Atomic number = same number of protons (differs because of the number of neutrons)

Atomic mass = Protons + Neutrons

Origin of Heavy Elements

Heavy Elements - were formed only billions of years after the formation of the stars

!! The density inside a star is great enough to sustain fusion for extended time periods required to synthesize heavy elements !!

Stars are hot and dense enough to burn hydrogen-1 (1H) to helium-4 (4He)

Stellar Nucleosynthesis - the formation of heavy elements by fusion of lighter nuclei in the interior of stars (Beryllium to Iron)

!! Layers near core of stars have very high temperatures enough to nucleosynthesize heavy elements such as silicon and iron !!

Elements heavier than Iron

Elements heavier than iron cannot be formed through fusion as tremendous amount of energy are needed for the reaction to occur

Supernova (massive explosion of a star) - heavier elements are formed here

Supernova - explosive death of a star

Neutron capture reaction - in supernova, this takes place, leading to formation of heavy elements

  • heavy elements are created by the addition of more neutrons to existing nuclei instead of fusion of light nuclei

!! Adding neutrons to a nucleus doesn't change an element. Rather, a more massive isotope of the same element is produced !!

Elements higher than iron - requires tremendous amount of energy to be formed. Thus, they were produced from a neutron capture reaction in a supernova

3 reactions that led to formation on elements

  1. Nucleosynthesis - formed light elements
  2. Fusion - formed elements with an atomic mass that is within the range of beryllium and iron
  3. Neutron capture reaction - formed elements that have atomic mass higher than iron

More energy, higher temperature - what is needed to form heavier elements

Cosmology (Cosmos - universe) - study of physical universe, its origin, evolution, and fate

Nuclear reactions - can describe the birth, life, and death of the stars.

Big Bang Theory - explains the continuous expansion of the universe.

  • theory by George Lamaitre

Supported by:

  1. CMB (Cosmic Microwave Background) - leftover radiation from Big Bang
  2. Red shift theory - the red shift of galaxies was directly proportional to the distance of the galaxy from earth
  • by Edwin Hubble

Hydrogen and Helium - earliest elements

Singularity - dense hot supermassive

Stellar nucleosynthesis - is a cosmological event when the elements beryllium to iron are formed through nuclear fusion

!! The formation of other elements not greater than iron occurs in the center of the stars where the temperature is about 15 million deg Celcius. !!

Supernova has two key requirements:

  1. the presence of extremely high temperature
  2. an abundant source of neutrons

Iron - most stable element >Nebula - a star originates from this large cloud of gas and dust

Protostar - when the nebula collapse due to its gravitational force it will become this

T-Tauri star - begins when materials stop falling into the Protostar and release tremendous energy.

!! The main sequence phase is the stage in development where the core temperature reaches the point for the fusion to commence. !!

!! When the hydrogen fuel runs out the star contracts inward through gravity
causing it to expand. As it expands, the star first becomes a subgiant star and then a red giant/ red super giant. !!

Red Supergiant - largest star in the universe

Neutron star - smallest star in the universe

Average star:

  1. Red giant star becomes exhausted of nuclear fuel; the outer material is blown off into space and becomes a white dwarf.
  2. When the white dwarf cools down and no longer emits light and heat, it will become a black dwarf.

Massive star:

  1. A massive star will experience a much more energetic and violent end. It
       explodes as a supernova.
  2. The remnant of the explosion will become a neutron star.
  3. Black hole - is a region in space where gravity is too strong that no matter can escape from it.

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