Lesson 6: Molecules and Compounds

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For this week’s lesson we are going to find out how to name chemical compounds.

Textbook Reading:  Chapter 5, pp. 127 – 153
Take a look at Problems 105 on page 160 and 107 on page 162

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Supplemental:

After reading the chapter, I’m sure you have some questions about naming molecules. Think of it as learning a new language, with rules of grammar and new vocabulary to learn. We’ll be going over examples in lab, but in the meanwhile here is some additional information that should help.

First, it would be really handy to have a copy of what is called a “Periodic Table of Ions.” This link to ScienceGeek has a free .pdf to download and print out if you don’t already have one.

Take a look at the Periodic Table of Ions and you will begin to see some patterns. The first group (first column of the periodic table) is called the alkali metals. They always give up an electron and become positive ions with a single +. The next group, the alkali earth metals, always give up two electrons, so they become ions with 2+. The next group (column 3), give up three electrons and are 3+.

The transition metals through the middle of the table don’t follow patterns as nicely and some have multiple states. That’s why we need a table to help us!

Over on the far right of the table, the wacky noble gases in column 18 do not give up electrons, which means they don’t form ions. They also are very stable and don’t form compounds with other elements. Next to the noble gases, the nonmetals tend to gain electrons and form negative ions. Group 17 is the first group to the left of the noble gases and is called the halides. They gain one electron and have  1- charged ions. At the top of column 17 notice that hydrogen has sneaked into this group as well, sometimes gaining an electron to become the hydride ion. In group 16 to the left, the atoms gain 2 electrons for 2- charged ions. Finally, the group 15 nonmetals gain 3 electrons for -3 charged ions. The rest do not form a clear pattern, and once again, you will need to refer to the table.

Hint:  Go back over the table and shade the groups with strong patterns with different colored pencils or highlighters.

Methane-3D-balls(Public domain image)

Are you ready to name this molecule with one carbon and four hydrogen atoms yet? It is commonly called methane, but that name doesn’t give you any information about its structure. How would you name it using the rules for naming molecules?

Mr. Anderson at Bozeman Science has two helpful videos about naming compounds. He goes over the same material as the text, but in a different way, which might help your understanding.

Naming Compounds – Part 1 (direct link)

Did you notice the name for the molecule above, CH4, at about 4:50 in the video? Did you find benzoate in your table of polyatomic ions on the Periodic Table of Ions printout?

Naming Compounds Part 2 (direct link)

Here’s a list of Greek words used in naming:
1= mono (isn’t used much
because the 1 is understood)
2 = di
3 = tri
4 = tetra
5 = penta
6 = hexa
7 = hepta
8 = octa
9 = nona
10 = deca

Want to reinforce your knowledge of the common polyatomic ions from Table 5.6 on page 141 in the text? Quizlet has flashcards and self-quizzes (with pronunciations).

As usual, please leave a comment or e-mail if you have any questions.

Edit:

Another way to remember those polyatomics (direct link)

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Optional:

This animation allows you to build models of some common molecules. To start, select a molecule in the box towards the middle.

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