2. CONTENT How the elements found in the universe were formed
CONTENT
STANDARD
At the end of the lesson, you will be able to demonstrate an
understanding of:
1. the formation of the elements during the Big Bang and
during stellar evolution
2. the distribution of the chemical elements and the isotopes
in the universe
LEARNING
COMPETENCIE
S
At the end of the lesson,
1. Give evidence for and describe the
formation of heavier elements during star
formation and evolution (S11/12PS-IIIa-2)
2. Describe how elements heavier than iron
are formed (S11/12PSIIIa-b-4))
7. is a form of a chemical
element whose atomic
nucleus contains a
specific number of
neutrons, in addition to
the number of protons
that uniquely defines the
8. is the process
by which a star
changes over
the course of
10. is the process by which the
natural abundances of the
chemical elements within
stars vary due to nuclear
fusion reactions in the cores
and overlying mantles of
13. is a theory of the production
of many different chemical
elements in supernova
explosions, first advanced
by Fred Hoyle in 1954.
16. This process happens when there is a slow rate of
capturing neutron while there is a faster rate of
radioactive decay hence increasing the proton by 1.
Example:
S-process or slow process
18. This means that there is faster rate of capturing neutron
before it undergoes radioactive decay thus, more
neutrons can be combined at the nucleus. This is what
happens in a supernova forming heavier elements than
Iron with the process known as supernova
nucleosynthesis
Example:
R-process or rapid process
21. What are the processes
involved in the
formation of heavier
elements?
22. is one of the two (known) sets of
fusion reactions by which stars
convert hydrogen to helium. It
dominates in stars the size of
the Sun or smaller.
24. The proton-proton chain reaction consists of three steps.
1. In the first step, two protons fuse at very high temperatures to create
a Deuterium nucleus (in this step, one of the protons actually
becomes a neutron, through beta-plus radioactive decay).
Deuterium has an atomic number of 1 and an atomic mass of 2 and
therefore is a heavy isotope of hydrogen.
2. Second, the deuterium nucleus fuses with a proton to form a
Helium-3 nucleus, which consists of 2 protons and 1 neutron.
3. Third step, two Helium-3 nuclei fuse together. This is an energetic
reaction that results in the release of 2 protons. The final product is
a Helium-4 nucleus, with 2 protons and 2 neutrons; this is also
referred to as the alpha particle.
25. is a set of nuclear fusion
reactions by which three helium-
4 nuclei (alpha particles) are
transformed into carbon.
27. Triple-Alpha Process: Step 1
In the first step, two helium nuclei combine to form a beryllium nucleus.
There is a conservation of atomic mass and the resulting nucleus has 4
protons and 4 neutrons (with an atomic number of 8).
Triple-Alpha Process: Step 2
Here, the beryllium nucleus formed in the previous step fuses with an
additional alpha particle, resulting in a carbon nucleus. The beryllium-8
produced from the previous reaction is highly unstable and therefore
either decays rapidly or reacts with an alpha particle to produce carbon.
It should be noted that not all the products of fusion in stars are stable.
In this example, the formation of beryllium-8 is important for the
formation of carbon-12, but the majority of beryllium actually formed
during the Big Bang (this is possible because it is such a light element).
28. is one of two classes of
nuclear fusion reactions by
which stars convert helium
into heavier elements, the
other being the triple-alpha
process.
30. Alpha Ladder Process
The general process, in which an alpha particle is
added to a nucleus results in a chain of reactions. This
set of reactions is also known as the alpha ladder. It
can form all the even elements from beryllium to iron.
The reactions proceed at a very low rate and do not
contribute significantly to the energy production in
stars, but are important for the generation of the
elements.
31. (for carbon–nitrogen–oxygen)
is one of the two known sets
of fusion reactions by which
stars convert hydrogen to
helium.
It is a catalytic cycle.
33. is any star that is fusing
hydrogen in its core and has
a stable balance of outward
pressure from core nuclear
fusion and gravitational
forces pushing inward.
35. is a dying star in the last stages of stellar
evolution. It is a large, bright star with a cool surface.
Its diameters is 10 to 100 times that of the Sun.
