Download Atoms and Elements

Index
Atoms and Elements
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Lesson 6 Index
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Scanning Tunneling Microscopes
Where do atoms come from?
The Big Bang and Stellar Fusion
Helium Burning and Red Giants
Supernovas and Neutron Stars
Second-Generation Stars
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Honors Chemistry Unit 02 Lesson 06
ARE ATOMS REAL?
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Scanning Tunneling Microscopes
• Scanning Tunneling Microscope (STM) – operates by
bring an atomically sharp tungsten probe ( only one or
two atoms across) near the surface of a sample, and
applying a voltage.
– A small electric current flows from the sample to the probe
in a process called electron tunneling.
– The strength of the current flow is sensitive to the distance
between the sample and the probe.
– By adjusting the distance between the sample and the probe
to keep the current constant, the probe traces a threedimensional image of the surface.
• STM’s can achieve magnifications of up to 10 million
times, allowing resolution of individual atoms.
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Where do atoms come from?
From the Big Bang to the Birth of the
Solar System
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The Big Bang and Stellar Fusion
• Most of the universe’s hydrogen was synthesized in
the first three minutes of the Big Bang, about 13.7
billion years ago, along with helium, and a light
dusting of lithium.
• As cosmic dust coalesces because of gravitational
attraction, a star forms, which generates heat and
light through the nuclear fusion of hydrogen to form
helium.
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4 1 H ® 2 He + 2 1 b + 2g + energy
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Helium Burning and Red Giants
• As its hydrogen is consumed, the star contracts, driving
the core temperature up, and helium is fused to form
heavier elements (as well as energy), ending up with iron
and nickel. This process is referred to as helium burning.
The outer layers of the star expand, producing a red giant.
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Supernovas and Neutron Stars
• Once a star starts producing iron-56, any further fusion
reactions consume energy. The star either becomes a white
dwarf, or, if the star was large enough, the core collapses,
and the outer layers of the star explode in a supernova.
• The core forms a neutron star, with a mass of 1.4 times that
of the Sun, with a radius of 10-20 km, and about the same
density as an atomic nucleus. If the star is larger, it
becomes a black hole.
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Second-Generation Stars
• The core’s collapse (briefly) provides enough
energy to drive fusion reactions that form
elements heavier than iron. The explosion’s
shock wave scatters these elements throughout
the neighboring space.
• These heavier elements become incorporated
into second-generation stars (such as the Sun),
and their associated planetary systems.
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