Formation of Light and Heavy Elements

Prepared By: Jerome A. Bigael, Leyte Progressive High School

The Origin of Light Elements

The origin of all the naturally occurring elements fall into two phases:

•Big Bang or Primordial Nucleosynthesis —the origin of the “light” elements; and

•Stellar Nucleosynthesis— the origin and production of the “heavy” elements.

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

Primordial or Big Bang Nucleosynthesisrefers to the process of producing the “light elements” shortly after the Big Bang.

The energy and temperature of the universe are extremely high to cause the neutrons and protons to combine and form certain species of atomic nuclei in a process called nuclear fusion.

Protons Neutrons

Through Nuclear Fusion, the light elements- Hydrogen (H), Helium (He), and small amounts of lithium (Li) and beryllium (Be) were formed.

The isotopes produced during the big bang nucleosynthesis were H-1, H-2, H-3, H-4, L-7.

An Isotope is a form of an element that has the same atomic number of the original element but with different atomic mass or mass number.

Origin of Heavier ElementsHeavy elements were formed only billions of years after the formation of 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).

The formation of heavy elements by fusion of lighter nuclei in the interior of stars is called “stellar nucleosynthesis”.

There are many nuclear synthetic pathways or nuclear fusions to produce heavy elements:

•Carbon-Nitrogen-oxygen cycle

•Proton-proton fusion

•Triple alpha process

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

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

Heavy elements are formed in a supernova, a massive explosion of a star.

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

A supernova is the explosive death of a star

In supernova, neutron capture reaction takes place, leading to formation of heavy elements.In a neutron capture reaction, heavy elements are created by 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.

Summary:There are 3 reactions that led to the formation of the elements: nucleusynthesis, fusion, and neutron capture reaction.

These reaction required a certain amount of energy to proceed, which was obtained from the heat of the continuously expanding universe. Thus energy in the form of heat does not only produce work but also the elements that make up matter that we have today.

The reaction involved in the formation of these elements are dependent on the atomic mass of the elements. More energy, and thus higher temperature, is needed to form heavier elements.

Nucleuosynthesis formed light elements, whereas fusion in stars formed elements with an atomic mass that is within the range of beryllium and iron. Thus any element with an atomic mass higher than iron, which required tremendous amount of energy to be formed was produced from a neutron capture -reaction in supernova.