Formation of the Elements and
Nuclear Reactions
Activity Card 1
Jumbled letters:
Direction: Arrange the following jumbled letters to form a word related to this lesson. Write
.
your answer in your activity notebook
a) S F N S I N O I
b) N H D G Y R E O
c) I S O U N F
d) V T G A Y R I
e) N O R T U E N
f) R S E U P S R U
g) R N G E E Y
h) S R A T S
i) G N A B G I B
j) V N S R U O A P
Elements are Formed in Different Ways in our
Universe
Activity Card 2
Complete the Table.
Direction: Identify whether the element in each number is “light” (lighter than iron),
“heavy” (heavier than iron), or “synthetic” (made synthetically in the lab.)
• _________1. hydrogen
• _________2. gold
• _________3 . copper
• _________4 . plutonium
• _________5. lithium
• _________6. oxygen
• _________7. silver
• _________8. magnesium
• _________9. americium
• _________10. neptunium
_________11. calcium
_________12. aluminum
_________13. nickel
_________14. titanium
_________15. sodium
_________16. potassium
_________17. californium
_________18. francium
_________19. nitrogen
_________20. carbon
Nucleosynthesis
• Nucleosynthesis is the process of element (nuclei) formation.
• Three types: Big Bang nucleosynthesis
Stellar (star) nucleosynthesis
Supernova nucleosynthesis
• Today, only stellar and supernova nucleosynthesis are
occurring in our universe.
• Element formation in our universe relies on nuclear fusion
reactions.
(fusion = come together)
Nuclear Fusion
• In nuclear fusion, smaller nuclei collide together
to make larger nuclei, and energy is released in
the form of electromagnetic radiation.
• Requires extremely high temperatures and
pressures beyond those found on or within
Earth. However, these temperatures and
pressures are found inside stars and did occur
during the initial formation of our universe
(during the Big Bang event).
• Fusion involves only the nuclei of atoms. At the
temperatures at which fusion can occur, matter
exists as a plasma. This is the state of matter
where the electrons have been stripped off of
the atoms. Plasma is basically a super high
energy, electrically charged gas.
• When nuclei collide, some of the mass of the
nuclei is converted to energy
by Einstein’s
2
famous equation, E=mc . Nuclear fusion
releases a lot of energy per gram of material;
much more energy than is released by burning a
comparable amount of wood, coal, oil, or
gasoline!
The Big Bang
• The Big Bang Theory is the most widely
accepted scientific theory about the origin of
the universe. It is supported by multiple lines
of evidence.
• The “Big Bang” was a phenomenally energetic
explosion that initiated the expansion of the
universe.
• At the moment prior to the Big Bang explosion,
all matter and energy were compressed at a
single point (a singularity – a point of infinite
density).
• We do not know what was before…..?
• The universe has been expanding ever since,
with galaxies moving farther and farther apart.
• Using the rates of expansion measured in the
universe and astronomical distances, the age
of the universe can be calculated back to the
time of the Big Bang. The age of the universe
is calculated at about 13.7 billion years old. By
contrast, our Sun and its surrounding planets
(i.e. our Solar System) is 4.65 billion years old.
Big Bang Nucleosynthesis
• All Hydrogen and most Helium in the universe was produced
during the Big Bang Event, starting ~100 seconds after the
explosion. A small amount of Lithium was also produced.
• Big Bang nucleosynthesis ceased within a few minutes after
the Big Bang because the universe had expanded and cooled
sufficiently by then such that the temperatures and pressures
were too low to support additional nuclear fusion reactions.
Stellar Nucleosynthesis
• A star is a very hot ball of gas (plasma). Stars create elements by combining lighter nuclei into
heavier nuclei via nuclear fusion reactions in their cores and releasing energy in the process.
They are natural nuclear reactors!
• Enormous temperatures (15,000,000 K), pressures, and densities of matter are needed to
initiate the fusion (thermonuclear) reactions which squeeze nuclei together and release energy.
• The basic nuclear reaction in the Sun converts hydrogen to helium and releases energy in the
form of electromagnetic radiation (see the basic fusion reaction below). This is why our Sun
shines!
• Our Sun is only large enough to fuse hydrogen into helium within its core.
Stellar Nucleosynthesis
• Stars much larger than our Sun can
fuse heavier elements from lighter
elements.
• These giant stars have an “onion
layer” structure.
• As you proceed deeper into the
star, temperatures and pressures
increase, and heavier and heavier
nuclei are fused together.
• The heaviest element that can be
made in a star is iron. Elements
heavier than iron have fusion
reactions with temperature and
pressure requirements greater than
those that can occur within the
core of a giant star.
• Note: In the adjacent diagrams, the
term “burning” really means
nuclear fusion!
Nuclear Fusion Requirements
(in stars)
Minimum Core
Temperature
Minimum Core
Density
Minimum Stellar
Mass*
He
13 million K
100 gm/cc
0.08 solar masses
Helium
C, O
100 million K
100,000 gm/cc
0.5 solar masses
Carbon
O, Ne, Mg, Na
500 million K
200,000 gm/cc
4 solar masses
Neon
O, Mg
1.2 billion K
4 million gm/cc
about 8 solar masses
Oxygen
Mg, Si, S, P
1.5 billion K
10 million gm/cc
about 8 solar masses
Silicon
Si, S, Ar, Ca, Ti, Cr, Fe,
Ni
around 3 billion K
30 million gm/cc
about 8 solar masses
Fusion
Fusion By-product
Hydrogen
gm/cc = grams per cubic centimeter (units of density)
https://sites.uni.edu/morgans/astro/course/Notes/section2/fusion.html
Supernova Nucleosynthesis
• Elements heavier than Iron (Z = 26) are
made primarily when giant stars explode
in supernovae.
• Even the largest stars do not have core
temperatures and pressures high enough
to fuse iron into heavier elements.
Therefore, when a star runs out of
nuclear fuel (lighter nuclei) and can no
longer undergo fusion reactions, gravity
causes the star to collapse. The
gravitational collapse triggers a
phenomenally large explosion called a
supernova. The explosion of the star
momentarily generates high enough
temperatures and pressures to cause
nuclear fusion reactions that make
elements with atomic numbers 27-92
(Cobalt to Uranium).
• Since only the largest stars can explode in
supernovae events, elements with
atomic numbers 27-92 are rarer than
elements with atomic numbers 1-26
(see abundance diagram to right)
An exploded star
(supernova)
Relative Abundance of the Elements in our Universe
A summary…
(You are made of stardust from exploded stars)