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2 CONTENTS UNIT 3 STARS & ELEMENTS BIG HISTORY PROJECT / UNIT 3 / STARS & ELEMENTS2 UNIT 3 BASICS 3Unit 3 Overview 4Unit 3 Learning Outcomes 5Unit 3 Lessons 6Unit 3 Key Concepts LOOKING BACK 8What Happened in Unit 2? KEY CONTENT 10How Were Stars Formed? 11Threshold 2: Stars Light Up 13A Big History of Everything 14Threshold 3—New Chemical Elements 15What Did Stars Give Us? 16Threshold 3: New Chemical Elements 18The Life Cycle of Stars 19A Little Big History of Silver 20Silver Supernova 21Mendeleev and Curie 22Ways of Knowing: Introduction to Chemistry 23Crash Course Chemistry: The Periodic Table LOOKING AHEAD 25 What’s Next in Unit 4?

3 3 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 BIG HISTORY PROJECT / UNIT 3 / STARS & ELEMENTS

4 4 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. BIG HISTORY PROJECT / UNIT 3 / STARS & ELEMENTS

5 5 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. BIG HISTORY PROJECT / UNIT 3 / STARS & ELEMENTS

6 6 UNIT 3 KEY CONCEPTS BIG HISTORY PROJECT / UNIT 3 / STARS & ELEMENTS carbon chemical element chemistry cluster cosmic horizon density fusion galaxy iron Milky Way galaxy neutron star periodic table of the elements periodicity plasma radioactivity star supercluster supernova


8 8 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. WHAT HAPPENED IN UNIT 2? BIG HISTORY PROJECT / UNIT 3 / STARS & ELEMENTS


10 10 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. BIG HISTORY PROJECT / UNIT 3 / STARS & ELEMENTS



13 13 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. BIG HISTORY PROJECT / UNIT 3 / STARS & ELEMENTS

14 14 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. BIG HISTORY PROJECT / UNIT 3 / STARS & ELEMENTS

15 15 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. BIG HISTORY PROJECT / UNIT 3 / STARS & ELEMENTS




19 19 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. BIG HISTORY PROJECT / UNIT 3 / STARS 7 ELEMENTS

20 20 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. BIG HISTORY PROJECT / UNIT 3 / STARS & ELEMENTS

21 21 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. BIG HISTORY PROJECT / UNIT 3 / THE STARS & ELEMENTS

22 22 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. BIG HISTORY PROJECT / UNIT 3 / STARS & ELEMENTS

23 23 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. BIG HISTORY PROJECT / UNIT 3 / STARS & ELEMENTS


25 25 WHAT’S NEXT? BIG HISTORY PROJECT / UNIT 3 / STARS & ELEMENTS 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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