There were three main reactions that led to the formation of elements: 1) Nucleosynthesis during the Big Bang formed the lightest elements hydrogen, helium, and lithium. 2) Nuclear fusion in stars formed heavier elements up to iron through processes like the proton-proton chain and triple alpha process. 3) Neutron capture reactions during supernovae formed elements heavier than iron, as they require more energy to form than can be provided by fusion. The temperature and density conditions of supernovae provided the right environment for these reactions.

1. Formation of
Light and
Heavy
Elements

2. THE FORMATION OF THE
ELEMENTS DURING THE BIGBANG
AND STELLAR EVOLUTION

3. 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.
The Origin of Light Elements

6. 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.

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.

8. Origin of Heavier Elements
 Heavy elements were formed only billions of
years after the formation of stars.
 Created when pairs of neutron stars collide
cataclysmically and explode
 The density inside a star is great enough to
sustain fusion for extended time periods
required to synthesize heavy elements.

9. Origin of Heavier 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”.

10. Origin of Heavier Elements
There are many nuclear synthetic pathways
or nuclear fusions to produce heavy
elements: •Carbon-Nitrogen-oxygen cycle
•Proton-proton fusion
•Triple alpha process

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

12. Elements heavier than Iron
Elements 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.

13. A supernova is
the explosive
death of a star

14. 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.

15. 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

16. 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.

17. Thank You