Question Video: Identifying the Ethane Molecule in a Set of Displayed Formulas | Nagwa Question Video: Identifying the Ethane Molecule in a Set of Displayed Formulas | Nagwa

Question Video: Identifying the Ethane Molecule in a Set of Displayed Formulas Chemistry • Third Year of Secondary School

Which of the following diagrams shows a molecule of ethane? [A] Diagram A [B] Diagram B [C] Diagram C [D] Diagram D [E] Diagram E

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Video Transcript

Which of the following diagrams shows a molecule of ethane?

The five diagrams provided are displayed formulas. They show all of the atoms and bonds in a molecule, and covalent bonds between atoms are drawn as lines. All five of the displayed formulas represent hydrocarbons. Hydrocarbons are molecules composed of only carbon and hydrogen atoms. Ethane is a type of hydrocarbon known as an alkane. This can be determined from its name. Alkanes are named using a prefix that indicates the number of carbon atoms present in the molecule. And the names of all alkanes end with the suffix A-N-E.

The following prefixes are used for the first five straight-chain alkanes. Here we can see that the prefix eth- indicates that an ethane molecule has two carbon atoms. If we want to find out how many hydrogen atoms an ethane molecule has, we need to know that an alkane is a saturated hydrocarbon. Saturated hydrocarbons contain only single covalent bonds between the carbon atoms. Alkanes have the general formula C𝑛H2𝑛+2, where 𝑛 is the number of carbon atoms in the molecule. We’ve already determined that ethane contains two carbon atoms, so 𝑛 equals two. To determine the number of hydrogen atoms in ethane, we can use the expression two 𝑛 plus two. After substituting two in for 𝑛, we get two times two plus two, which equals six.

Now that we’ve determined that an ethane molecule contains two carbon atoms and six hydrogen atoms, let’s sketch a displayed formula. Let’s begin by connecting two carbon atoms with a single bond. Next, we can connect the six hydrogen atoms to the carbon atoms using single bonds. It’s helpful to remember that each carbon atom should be surrounded by a total of four bonds. Here, we can see that the carbon atom on the right is surrounded by four bonds and that the carbon atom on the left is also surrounded by four bonds.

Now that we have a displayed formula of ethane, let’s take a look at the answer choices. We can see that all of the molecules are straight-chain alkanes like ethane. But only the displayed formula in answer choice (B) contains the correct number of carbon atoms and matches our drawing. Therefore, the diagram showing a molecule of ethane is answer choice (B).

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