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STARS & ELEMENTS
HOW CAN LOOKING AT THE SAME INFORMATION FROM
DIFFERENT PERSPECTIVES PAVE THE WAY FOR PROGRESS?
UNIT 3
STARS & ELEMENTS
CONTENTS
UNIT 3 BASICS
3 Unit 3 Overview
4 Unit 3 Learning Outcomes
5 Unit 3 Lessons
6 Unit 3 Key Concepts
LOOKING BACK
8 What Happened in Unit 2?
KEY CONTENT
10 How Were Stars Formed?
11 Threshold 2: Stars Light Up
13 A Big History of Everything
14 Threshold 3—New Chemical Elements
15 What Did Stars Give Us?
16 Threshold 3: New Chemical Elements
18 The Life Cycle of Stars
19 A Little Big History of Silver
20 Silver Supernova
21 Mendeleev and Curie
22 Ways of Knowing: Introduction to Chemistry
23 Crash Course Chemistry: The Periodic Table
LOOKING AHEAD
25 What’s Next in Unit 4?
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UNIT 3
OVERVIEW
Key Disciplines:
Physics, astronomy, and chemistry
Timespan:
The first stars appeared about 13.6 billion years ago
Driving Question:
How can looking at the same information from different perspectives pave the way for progress?
Thresholds for this Unit:
Threshold 2: The Stars Light Up
Threshold 3: New Chemical Elements
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UNIT 3
LEARNING OUTCOMES
By the end of Unit 3, students should be able to:
1.
Describe how stars form.
2.
Explain what happens in the life of a star and explain what happens when a star dies.
3.
Explain how the death of stars results in the creation of heavier elements.
4.
Explain why the formation of stars and the emergence of elements are so important in our
world.
5.
Understand what scholars from multiple disciplines know about a topic and the questions they
can ask to gain an understanding of the topic from an integrated perspective.
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UNIT 3
LESSONS
3.0 How Were Stars Formed?
The first stars formed when gravity condensed massive clouds of hydrogen and helium so much
that fusion could begin, producing heat and light. Stars represented a significant increase in the
complexity of the Universe.
3.1 Creation of Complex Elements
The Big Bang formed lots of hydrogen and helium but not much else. Where do all the other
elements come from? Aging and dying stars reproduce the temperatures and pressures of the early
Big Bang, allowing for the formation of the heavier elements.
3.3 Ways of Knowing: Stars and Elements
All those new elements—what exactly were they and how did they bind to or repel each other? The
science of chemistry was born as early scientists studied the properties and structure of chemical
elements and compounds.
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UNIT 3
KEY CONCEPTS
• carbon
• periodic table of the elements
• chemical element
• periodicity
• chemistry
• plasma
• cluster
• radioactivity
• cosmic horizon
• star
• density
• supercluster
• fusion
• supernova
• galaxy
• iron
• Milky Way galaxy
• neutron star
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LOOKING BACK
WHAT HAPPENED
IN UNIT 2?
Unit 2 provided a history of human views of the Universe and depicted the early years
following the Big Bang.
• Big History begins with the Big Bang.
• Scientists used the tools of their time to understand the Universe, with each generation building
on the work of earlier generations.
• Edwin Hubble discovered that the Universe was expanding, and laid the groundwork for the
development of the Big Bang theory.
• Space, time, matter, and energy were created in the Big Bang.
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KEY CONTENT
HOW WERE STARS
FORMED?
Video Talk / David Christian
• Stars formed when clouds of hydrogen atoms were brought together by gravity.
• As the clouds became increasingly dense, temperature and pressure rose dramatically and the
hydrogen atoms at the center of each cloud began to fuse into helium atoms.
• This process, called fusion, released tremendous amounts of energy and balanced the pull of
gravity, which was trying to fuse the core of each cloud into an even denser mass.
• As the two forces (gravity and fusion) reached a balance in each cloud, a star was born.
• When a number of stars had been born, the force of gravity began attracting stars into groupings
called galaxies. Gravity also grouped galaxies into clusters and clusters into superclusters.
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A BIG HISTORY OF
EVERYTHING
Video
• The early Universe was very simple, consisting mainly of hydrogen and helium atoms but
lacking in any larger, more complex structures.
• A few hundred million years after the Big Bang, stars began to form from the the clouds of
hydrogen and helium strewn throughout the Universe.
• Gravity was the most important force driving the process of star formation. All matter is affected
by gravity, including tiny little atoms.
• Gravity took advantage of the differences in the size of the clumps of atoms in these clouds,
adding smaller clumps to create larger and larger ones. This caused temperature and pressure
to rise in the clouds. Once the core of these clouds reached a temperature of 10 million degrees,
the hydrogen atoms began to fuse together to form helium and a star was born.
• Stars made the Universe different and more complex. Before stars, all sources of energy had
been created by the Big Bang. Stars created energy in the form of heat and light.
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THRESHOLD 3—NEW
CHEMICAL ELEMENTS
Video
• How a star lives and dies is determined in large part by its size. Bigger, denser stars burn hotter
and run out of fuel more quickly than small or medium stars. Star death can create the
temperatures and pressures necessary for star formation.
• The ingredients necessary for the formation of the chemical elements are very high
temperatures and aging and dying stars.
• The Goldilocks Conditions necessary for the formation of new chemical elements are stars
running out of their fuel and giant stars collapsing.
• The death of medium- and large-sized stars can generate temperatures and pressure high
enough to create all the elements up through iron.
• The death of very large-sized stars can generate temperatures and pressure high enough to
create all the elements up through uranium.
• The most massive stars die in supernova explosions, which are the biggest most spectacular
explosions in the Universe. A supernova can shine with the brightness of an entire galaxy.
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WHAT DID
STARS GIVE US?
Video Talk / David Christian
• Hydrogen and helium formed in the early moments after the Big Bang. They are the simplest
naturally occurring elements and were formed in great quantities as the early Universe cooled.
• Much higher temperatures and pressures are required to create bigger, more complex elements.
Dying stars are the one place that provide the right conditions.
• When large stars die, they can achieve temperatures of 3 billion degrees, which is hot enough to
create iron atoms through fusion. The death of large stars can produce numerous heavy
elements.
• The supernova death of a high-mass star generates many of the heavy elements in the periodic
table and disperses them into space.
• The formation of new chemical elements was only possible through the death of stars, and the
creation of these elements made a more complex Universe possible.
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THE LIFE CYCLE
OF STARS
Infographic
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A LITTLE BIG HISTORY OF
SILVER
Article
• Each element has properties that make it unique.
• Silver is valued for its shy and attractive appearance. It is also relatively soft, so it can be molded
into jewelry and coins. It doesn’t react easily with other elements, so it won’t corrode like some
other metals. At the same time, silver is a relatively scarce element, which makes it valuable.
• Silver has played an important role in history. It was valued by the Minoans and Myceneans,
early Greek peoples that imported silver minted in Armenia. Silver was also highly valued in
China. Because it was scarce, the Chinese were willing to trade for it. Much of this silver flowing
into China during the Ming Dynasty came from Spanish sliver mines in Mexico and Bolivia.
Silver formed the basis for the first global currency in the seventeenth century.
• Silver was also valued for other reasons as well: it was considered to have great healing
powers, it is considered the best metallic conductor of electricity, and its low friction makes it
good for many purposes, including its use as ball bearings in jet engines.
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SILVER SUPERNOVA
Video
• Silver creation requires very high temperatures, so it can only be created in supernova
explosions Gold is a rarer element, as it is not created in every supernova explosion. Gold
requires the collision of two neutron stars, which occurs far less often. As a result, we have
about 10 times less gold than silver.
• Volcanic activity tends to create concentrations of metals, pushing them to the surface. As a
result, you will often find deposits of silver in areas where there has been significant volcanic
activity.
• The discovery of a large vein of silver allowed the Greeks to expand to build more ships and pay
a large army, which helped them to defeat the Persians. The discovery of silver in South America
enabled the Spanish to transport much of this silver across the Pacific Ocean to the Philippines
and China to pay for valuable Chinese exports.
• Silver coins from the Thale Valley were traded throughout Europe. These coins were called
Thalers. Eventually the word applied to any silver coin. In English, the word Thaler became
dollar. In the early days of the United States, the government did not have a mint to create coins.
People used the Spanish peso to buy and sell goods. On this coin was a scroll wrapped around
a column that many believe was the inspiration for the dollar sign.
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MENDELEEV AND CURIE
Articles / Cynthia Stokes Brown
In this set of articles, Cynthia Stokes Brown provides
biographies of key figures who contributed to our changing view
of the chemistry and the chemical elements.
• Dimitri Mendeleev organized the periodic table that we use
today. Though he did not know about all of the elements, he
was able to accurately predict where on the table some
undiscovered elements belonged and what properties they
would have.
• Marie Curie did important work in both chemistry and
physics. Her discoveries about radioactivity and its
relationship to the atom contributed greatly to the emerging
view of the nature of the atom in the early twentieth century.
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WAYS OF KNOWING:
INTRODUCTION TO
CHEMISTRY
Video Talk/Anne McNeil
• Anne McNeil is a professor of chemistry at the University of Michigan.
• Chemistry is broadly defined as the study of matter.
• Chemists typically focus on two important characteristics of matter in their work: composition
and structure. Composition is defined as the elements that make up a chemical compound.
Structure is defined as the way those elements are arranged within the molecule.
• Compounds with the exact same composition can have different structures that result in big
differences in their physical properties. For example, diamonds and graphite are both made of
carbon, but because of the different arrangements of the atoms in each compound they have
immensely different properties.
• Chemists used to have very limited techniques for analyzing matter—like tasting them! Today,
chemists use a variety of techniques including x-rays to study the connections between atoms,
mass spectrometers to study the mass of molecules, and spectroscopy help study the types of
bonds in matter.
• Chemistry is often described as the central science because it is important in the work of
scientists in a wide range of other fields. Today there are many different types of chemists,
including astrochemists, geochemists, biochemists, chemical biologists, analytical chemists,
material chemists, and synthetic chemists.
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CRASH COURSE CHEMISTRY:
THE PERIODIC TABLE
Video
• The creation of the periodic table is one of the most important achievements in the history of
chemistry. When Dmitri Mendeleev published his first periodic table, people knew quite a bit
about individual elements, but how the elements related to each other was not at all clear.
Mendeleev’s helped revolutionize how we see the world.
• In Mendeleev’s time about 60 elements were known, and the atomic weights of most of these
elements had been determined. Many more elements and the nature of atoms awaited
discovery.
• Today electrons are critical to understanding the relationships between different elements, but
protons, neutrons, and electrons had not been discovered in Mendeleev’s time, so he had to
organize his table based on other factors.
• What makes the periodic table “periodic” are the patterns or trends it helps illuminate. The
lightest elements, for example, in the first row are not all that alike, but every eighth element has
a lot in common. Numbers like eight are important in understanding the patterns in the table.
• Groups of elements in the table also shared important characteristics. The ability of an element
to react with other elements, or not, was an important consideration for chemists in Mendeleev’s
day, so considerations like those influenced how he organized the table.
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BIG HISTORY PROJECT / UNIT 3 / STARS & ELEMENTS
LOOKING AHEAD
WHAT’S NEXT?
In Unit 4, we will focus on the Solar System and our planet, Earth. We will learn:
• How Earth and the rest of our Solar System formed over a very long period of time
• About the Earth’s violent and unstable beginning
• How plate tectonics keep the Earth’s surface in constant motion
• How we learn about the Earth’s changes over time through the science of geology
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