1. The molecule shown in the figure has two blue spheres.
QUESTION:
Which of these is not the formula of the compound represented by the figure below, if blue spheres represent carbon atoms, white spheres represent hydrogen atoms and red sphere represents an oxygen atom? A. CHO, B. C2H6O C. C2H5OH,
D. CH3CH2OH
The formula of a molecular compound reflects the composition of each molecule in the compound. Subscripts indicate how many atoms of each kind are present in the molecule.
SCRIPT:
Which of these is not the formula of the compound represented by the figure here, if blue spheres represent carbon atoms, white spheres represent hydrogen atoms and red sphere represents an oxygen atom? A. CHO, B. C2H6O C. C2H5OH,
D. CH3CH2OH
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The formula of a molecular compound reflects the composition of each molecule in the compound. Subscripts indicate how many atoms of each kind are present in the molecule.
The molecule shown in the figure has two blue spheres.
HIGHLIGHT Since, according to the question, blue spheres represent carbon atoms, we should see carbon written in the formula with a subscript of 2, as in choices B and C,
HIGHLIGHT C2 in choices B and C
or written twice with no subscript, as in choice D.
HIGHLIGHT C in CH3 and C in CH2
Remember that a subscript that is not written is implied to be one.
Obviously, then, … choice A is NOT a correct formula for the compound represented in the figure.
Therefore, the correct answer is A.
Let’s look more closely at choices B, C, and D to verify that they are all correct formulas.
In the figure, we see six white spheres,
HIGHLIGHT as you call out
1…2…3…4…5…6
These represent six hydrogen atoms. Therefore, H should appear in the formula so that the total subscript is 6.
In choice B, the subscript of hydrogen is 6.
HIGHLIGHT In choice C, hydrogen is written twice and the total subscript is also equals 6.
HIGHLIGHT In choice D, hydrogen is written three times,
HIGHLIGHT with subscripts of 3, 2 and 1. … equals 6.
As far as hydrogen is concerned, we can see that choice A is incorrect. Hydrogen appears in choice A only once, and with no subscript.
Finally, the molecule shown in the figure has one red sphere, which represents an oxygen atom.
Oxygen appears in all the choices All the choices given have one oxygen with no subscript.
The compound represented here is ethanol. It belongs to a class of compounds known as organic compounds.
Its formula is, in fact, written more frequently like in choices C and D.
The CH3 grouping…
HIGHLIGHT CH3 in choice D and CH3 in the figure
is quite common among organic compounds. It’s called a methyl group.
CALLOUT “methyl”
The CH2 grouping…
HIGHLIGHT CH2 in choice D and CH2 in the figure. It’s called a methylene group.
The CH3CH2 grouping…,
HIGHLIGHT CH3CH2 in choice D
which is often abbreviated C2H5…
HIGHLIGHT C2H5 in choice C
is also quite common and is called an ethyl group.
The OH group…
HIGHLIGHT OH in choices C and D and in figure
CALLOUT “hydroxyl” pointing to OH group is also quite common among organic compounds. It’s called a hydroxyl group. Compounds whose molecules have hydroxyl groups are called alcohols. Ethanol is also called ethyl alcohol.
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2. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08