Transcript Origin of the Elements

Origin of the Elements
The Creation of the Universe
 There are many theories of how the universe was
created. One theory developed by Einstein, Hoyle, and
others is called the “Steady State Theory.”
 The current and most popular theory of the creation
of our universe is called the “Big Bang Theory.”
 The Big Bang Theory states that the universe formed
about 14 billion years ago and has been expanding
ever since.
 All theories show that matter was formed at a very
early stage in the history of our universe.
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In the Beginning - Gas
The first elements to form in our universe were
hydrogen and deuterium, both gases.
 Hydrogen has one proton and one
electron:
1H
 Deuterium is an isotope of
hydrogen. It has one proton, one
electron, and one neutron:
2D
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How is Deuterium Formed?
Deuterium is formed when hydrogen atoms disintegrate
into protons, which break down into a neutron and a
positron, a positively charged electron:
-
+
+
Protons, neutrons and electrons are the basic parts of atoms
that are used to create all the other elements in the periodic table.
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Deuterium Formation
Protons fuse with neutrons and add electrons to form
deuterium:
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The gases combine to form stars
 Gravity caused the gases to condense into clumps of atoms
at very high pressures that formed the first stars. These
stars were hundreds of times larger than our Sun.
 Deep within the center of these gigantic stars the
temperature reached hundreds of thousands or even
millions of degrees Celsius.
 These high temperatures and pressures caused the
hydrogen and deuterium to form helium in a process
called nuclear fusion, which is sometimes unfortunately
called “burning” although it is not combustion.
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Nuclear Fusion – the First Steps
Two deuterium atoms can fuse to form helium:
4
He
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Nuclear Fusion Continues
Gamma rays,
electrons and
photons as well
as sub-atomic
particles called
neutrinos and
positrons are
produced under
the extreme
conditions in
stars.
Source: Sky & Telescope, March 2008, 26
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Nuclear Fusion Inside the Stars
 The extremely high temperatures and pressures
generated by nuclear fusion causes helium nuclei,
also known as alpha particles, to be converted into
elements with larger and larger masses.
 The so-called Triple Alpha Process shows how
helium is converted into beryllium and carbon
during this burning process.
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Source: Sky & Telescope, March 2008, 26
Nuclear Fusion – The Elements of Life
Once carbon, the first key element of life, is formed, the
other life supporting elements, oxygen and nitrogen, are
formed in what is called the CNO Cycle.
Source: Sky & Telescope, March 2008, 26
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Evolution of Stars
 Stage 1 - When the star is first formed only helium
(He) is formed at the core.
 Stage 2 - After the hydrogen is used up in the core,
the helium begins fusing into carbon (C) at its core,
but hydrogen continues to form helium in a thin
layer farther out.
 Stage 3 – the star swells to become a “red giant” and
the smaller elements fuse to former larger and
larger elements.
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Stage 1
Stage 2
Stage 3
Red Giant
Source: Sky & Telescope, March 2008, 26
Evolution of Stars
 Stage 4 – Elements such as sodium (Na), neon
(Ne), magnesium (Mg), oxygen (O), sulfur (S), and
silicon (Si) are formed in the outer layers.
The heavier elements are formed closer to the core
and eventually fuse in the core of the star to form
iron (Fe), the most massive element found in stars.
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Stage 4
Source: Sky & Telescope, March 2008, 26
Forming Heavier Elements in Supernova
 After a star reaches its maximum stage in several
billion years, a massive explosion called a
“Supernova” will blow the star apart.
 The extreme temperatures that occur during this
explosion, are estimated to be more than 100
million degrees Celsius. This enables atoms and
neutrons to be released at an enormous rate.
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The Crab Nebula – Remains of a Supernova Explosion
Source: Sky & Telescope, March 2008, 32
Forming Heavier Elements in Supernova
 Neutrons are captured by atoms to form
more massive elements.
Source: Sky & Telescope, March 2008, 32
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Forming Heavier Elements in Supernova
 When an atom captures a neutron, it becomes
a heavier isotope of the same atom.
 In unstable isotopes, a neutron decays into a
proton, electron and neutrino, converting the
atoms into the next element in the periodic
table.
 The process continues until all the heavier
elements are produced.
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How did the elements reach Earth?
 When stars and supernova explode, they send
burning pieces of mass in all directions.
 These hot masses, which contain the elements,
spread throughout the universe to eventually
form other stars and planets.
 Our solar system was created in this way over
a period of many billions of years.
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A Planetary Nebula – Remains of an Exploding Star
NGC5315
7,000 light
years away
Source: Sky & Telescope, March 2008, 32
Bibliography
1. Beers, Timothy C., “Origin of the Elements of
Life,” Sky & Telescope, March 2008, 26.
2. James, C. Renee, “Where Did You Come
From?” Sky & Telescope, March 2008, 32.
3. Ziurys, Lucy M., “The Chemistry in
Circumstellar Envelopes of Evolved Stars,”
Proc. of Nat’l Acad. of Sciences, 103, (33) 12274
(2006).
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