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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.