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Weekly Web Work #6:
Ions and Ionic Compounds
This assignment was due by noon on Tuesday, February 18, 2003.
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The purpose of this week"s assignment is to predict ion charges and to begin to write chemical formulas for ionic compounds.
The electron configurations of the noble gases are extremely stable. When an atom undergoes a chemical change to become an ion, the atom will gain or lose electrons until it is isoelectronic (has the same electron configuration) with the nearest noble gas. Metals tend to lose electrons and form positively charged ions called cations. Non-metals tend to gain electrons and form negatively charged ions called anions.
For example, sodium metal, Na,
Ionic compounds are composed of metal cation(s) and non-metal anion(s) and have a net charge of zero. Sodium chloride, NaCl, is composed of Na+ and Cl– in a one to one ratio which gives the formula zero charge. When writing the formula for an ionic compound, the symbol for the cation is written first.
Note that forming ions from neutral atoms is a chemical reaction. Click here to view sodium metal and chlorine gas reacting to form sodium chloride. This video clip is from the McMurry textbook companion web site (http://cwx.prenhall.com/bookbind/pubbooks/mcmurrygob/). If you can"t view the reaction, there is a picture of it on page 74 in your text.
The following questions are designed to help you begin to think about ions and ionic compounds. You may wish to look at chapter 4 section 7 (page 79-81) and section 10 (bottom of page 84-87) in your textbook.1.
|Predict the formula of the compound formed when lithium and fluorine react. (Remember, elements in the same group react similarly.)|
|2.||Predict the formula of the compound formed when potassium and iodine react.|
|3.||What ion will magnesium form?|
|4.||What ion will oxygen form?|
|5.||What ion will aluminum form?|
When writing the formula for ionic compounds, the total positive charge from the cations plus the total negative charge from the anions must add up to zero for the formula to have a zero net charge. When writing formulas for an alkali metal reacting with a halogen, the ratio of ions is one to one. Remember our example of NaCl above? NaCl is composed of Na+ and Cl– ions. So 1(1+) + 1(1-) = 0
What about the compound that forms when calcium reacts with bromine? Calcium forms the 2+ ion, Ca2+, because it needs to lose 2 electrons to be isoelectronic with argon. Bromine forms the 1- ion, Br–. The formula for calcium bromide is CaBr2. You need two bromide ions to balance the 2+ charge of the calcium ion so that the formula will have no charge. 1(2+) + 2(1-) = 0
|6.||Predict the formula of the compound formed when aluminum and chlorine react.|
|7.||Explain the thought process you used to figure out the formula for aluminum chloride in question 6.|
|8.||Predict the formula for the compound formed when potassium and oxygen react.|
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|Explain the thought process you used to figure out the formula for potassium oxide in question 8.|
You can edit your responses until you are satisfied with your answers. Remember, the purpose of the assignment is to help you think about a topic. Your answers don"t have to be "right" to get credit, you just need to answer the questions with your best effort.
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