In Lewis dot structures, cations have fewer valence electrons because, remember, cations are positive since they are losing electrons; anions have more valence electrons, and an anion is a negative ion because it's gaining electrons. So using this, let's answer this example question. It says draw the Lewis dot structure for the following anion, BCl4-. Alright. So here we have to determine the total number of valence electrons of the structure. And recall that valence electrons equal the group number of the element. So here we have boron, which is in group 3A, and there's one of them. We have chlorine, which is in group 7A, and there are 4 of them. That's 28. And then remember that this minus one means we've gained an electron. So we're going to add 1 electron to this mix, giving us a total of 32 valence electrons. Now, we're going to place the least electronegative element in the center and connect all elements with single bonds. We're going to follow our bonding preferences guide to determine atom connectivity. Now, if you haven't watched my video on bonding preferences, I highly suggest you go back and take a look because it helps you to identify what kind of bonds these elements like to make—2 bonds, 3 bonds, etc. So here we're going to place boron in the center, and we're going to make single bonds to each of the chlorines. Now we're going to add electrons to all surrounding elements until they have 8 electrons because we're trying to follow the octet rule. Now remember, hydrogen doesn't follow the octet rule; it follows the duet rule. It only wants 2 valence electrons around it, so that it can be just like helium. So, I'm adding enough electrons so that each chlorine is following the octet rule. Now place any remaining electrons on the central element or central atom. So we've already used all 32 of our electrons here, so there's none left. Step 5 says that we need to place the ion in brackets and its charge in the top right corner. So that's right. For ions, once you draw the Lewis dot structure, you have to put it in brackets with the charge on the outside. So brackets around it, and you'd put the minus charge here. Here I'm going to bring it down so we can see it better. So here goes boron with the 4 chlorines that it's attached to. So here go our 4 chlorines that we're attached to. Since it's an ion, put it in brackets, and the charge on the outside and top right corner. Now for cations, this is not a cation, but for cations, remove valence electrons from the central element. So just keep that in mind when dealing with cations. So these would be the rule that we use in order to draw either cations or anions when asked to determine the Lewis dot structure.
4. Molecular Compounds
Lewis Dot Structures: Ions (Simplified)
4. Molecular Compounds
Lewis Dot Structures: Ions (Simplified) - Video Tutorials & Practice Problems
Lewis Dot Structures of Ions involves losing or gaining valence electrons to draw the most likely structure.
Lewis Dot Structures of Ions
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Lewis Dot Structures: Ions (Simplified) Concept 1
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Problem
ProblemDraw the Lewis Dot Structure for the following cation:NH4+.
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ProblemDetermine the Lewis Dot Structure for the following ion:O22–.
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ProblemDetermine the Lewis Dot Structure for the following ion:SCl42+.
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ProblemDraw the Lewis Dot Structure for the following ion:PCl4+.
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