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Elements&Compounds Name______________________ Hour_________ Although matter can take many different forms, all matter can be broken down into a relatively small number of basic building blocks called elements. An element is a pure substance that cannot be separated into simpler substances by physical or chemical means. On Earth, over 90 elements occur naturally. Copper, oxygen, and gold are examples of naturally occurring elements. There are also several elements that do not exist naturally but have been developed by scientists. Each element has a unique chemical name and symbol. The chemical symbol consists of one, two, or three letters; the first letter is always capitalized, and the remaining letter(s) are always lowercase. The names and symbols of the elements are universally accepted by scientists in order to make the communication of chemical information possible. The naturally occurring elements are not equally abundant. For example, hydrogen is estimated to make up approximately 75% of the mass of the universe. Oxygen and silicon together compromise almost 75% of the Earth’s crust, while oxygen, carbon, and hydrogen account for more than 90% of the human body. Francium, on the other hand, is one of the least-abundant naturally-occurring elements. There is probably less than 20 grams of francium dispersed throughout Earth’s crust. Elements are found in different physical states in normal conditions. As many new elements were being discovered in the early nineteenth century, chemists began to observe and study patterns of similarities in the chemical and physical properties of particular sets of elements. In 1869, Russian chemist Dmitri Mendeleev (1834-1907) devised a chart, which organized all of the elements that were known at the time. His classification was based on the similarities and masses of the elements. Mendeleev’s table was the first version of what has been further developed into the periodic table of the elements. The periodic table organizes the elements into a grid of horizontal rows called periods and vertical columns called groups or families. Elements in the same group have similar chemical and physical properties. The table is called periodic because the pattern of similar properties repeats from period to period. Many pure substances can be classified as compounds. A compound is made up of two or more different elements that are combined chemically. Most matter in the universe exists in the form of compounds. Today there are more than 50 million known compounds, and new compounds continue to be developed and discovered at the rate of about 100,000 per year. There appears to be no limit to the number of compounds that can be made or that will be discovered. Considering this virtually limitless potential, several organizations have assumed the task of collecting data and indexing the known chemical compounds. The information is stored in databases. The chemical symbols of the periodic table make it easy to write the formulas for chemical compounds. For example, table salt, which is called sodium chloride, is composed of one-part sodium (Na) and one-part chlorine (Cl), and its chemical formula is NaCl. Water is composed of two parts hydrogen (H) and one-part oxygen (O), and its chemical formula is H2O. The subscript 2 indicates that two hydrogen elements combine with one oxygen element to form water. Elements&Compounds Name______________________ Hour_________ Elements can never be separated into simpler substances. However, compounds can be broken down into simpler substances by chemical means. In general, compounds that occur naturally are more stable than the individual component elements. Separating a compound into its elements often requires external energy, such as heat or electricity. Through a process called electrolysis water can be separated into its component elements. During electrolysis, one end of a long platinum electrode is exposed to the water in a tube and the other end is attached to a power sources. An electric current splits water into hydrogen gas in the compartment on the right and oxygen gas in the compartment on the left. Because water is composed of two parts hydrogen and one-part oxygen, there is twice as much hydrogen gas as there is oxygen gas. The properties of a compound are different from those of its component elements. The example of water illustrates this. Water is a stable compound that is liquid at room temperature. When water is broken down, its components, hydrogen and oxygen, are dramatically different than that of the liquid they form when combined. Oxygen and hydrogen are colorless, odorless gases that undergo vigorous chemical reactions with many elements. This difference in properties is a result of a chemical reaction between the elements. Things we are specifically searching for: 1) What is an element and how can we identify one? 2) What is a compound and how is it different from the elements in it? 3) What is the purpose of the periodic table? Elements&Compounds Name______________________ Hour_________ 1. What is an element? 2. How many elements occur naturally on Earth? 3. How can elements be identified? 4. What element makes up a majority of the universe’s mass? 5. What elements make up a majority of the Earth’s crust? 6. What characteristics of elements did Mendeleev use to order his chart of the elements? 7. What is the periodic table? Where did it first originate? 8. How does the periodic table organize elements? 9. What does it mean if 2 elements are in the same group in the periodic table? 10. Where did the periodic table get its name? 11. What is a compound? 12. Does most matter in the universe exist in the form of elements on their own or compounds? 13. How many compounds are there? Have we discovered all the different types of compounds? 14. The letter C is the symbol for Carbon and the letters Cu are the symbol for Copper. What would C3Cu2 stand for? 15. Which is more stable a singular element or a compound? 16. Can an element be broken down into different substances? 17. You’re a scientist and you want to separate table salt into sodium and chloride. What will you likely need in order to complete the breakdown of the compound? 18. The letters Si are the symbol for the element silicon and the letter H is the symbol for the element hydrogen. What would Si3H stand for? 19. Does a compound have all the same characteristics of the elements that make it up or does a compound have characteristics different from the elements that make it up? Explain and provide an example. Elements&Compounds Name______________________ Hour_________ 1. What is an element? 2. How many elements occur naturally on Earth? 3. What are some examples of naturally occurring elements? 4. How can elements be identified? 5. In the first sentence of the 3rd paragraph, what is the intended meaning of the word “abundant”? 6. What element makes up a majority of the universe’s mass? 7. What elements make up a majority of the Earth’s crust? 8. What elements make up a majority of the human body? 9. If you were to take a sample of the Earth’s crust and examine it? What do you think chances are you would find francium in your sample? What about silicon? Defend your answer. 10. In the last sentence in paragraph 4 what does it mean by “Elements are found in different physical states in normal conditions.”? 11. What characteristics of elements did Mendeleev use to order his chart of the elements? 12. What is the periodic table? Where did it first originate? 13. How does the periodic table organize elements? 14. What does it mean if 2 elements are in the same group in the periodic table? 15. Where did the periodic table get its name? 16. What is a compound? 17. Does most matter in the universe exist in the form of elements on their own or compounds? 18. How many compounds are there? Have we discovered all the different types of compounds? 19. The letter C is the symbol for Carbon and the letters Cu are the symbol for Copper. What would C3Cu2 stand for? 20. Which is more stable a singular element or a compound? 21. Can an element be broken down into different substances? 22. You’re a scientist and you want to separate table salt into sodium and chloride. What will you likely need in order to complete the breakdown of the compound? 23. The letters Si are the symbol for the element silicon and the letter H is the symbol for the element hydrogen. What would Si3H stand for? 24. Does a compound have all the same characteristics of the elements that make it up or does a compound have characteristics different from the elements that make it up? Explain and provide an example.