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Problem 10 Easy Difficulty

Indicate the substance that contains the smallest cation.
(a) $\mathrm{BaCl}_{2} ;$ (b) $\mathrm{Al}_{2} \mathrm{O}_{3} ;$ (c) $\mathrm{Mg}_{3} \mathrm{N}_{2} ;$ (d) SrS

Answer

Al2O3 has the smallest cation, which is Al3+

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Video Transcript

So this is question 11.10 in chemistry, the science and context at the end of chapter 11. So it asks which of the following compounds has the smallest cat eye on a case of the cat ion, remember, is the positively charged ion. So in here are cat ion is e a two plus Here it's gonna be aluminum three plus k, this one magnesium young and this one strong tm two plus. OK, so these are the cat ions, um, of these compounds. Okay. And if you forgot how to get the cat ions from the, um from the caught the chemical compound formula, previous chapters in the book explain that, but essentially so in, for example, of barium chloride. I know that chlorides like to be each chloride is a negative. So that means that I have to have barium two plus, um since chloride there's two of them, right? Another thing is based on their groups. Right? So barium, magnesium, strontium are all in the group number two. So I know that they're all going to be two plus when they become cat ions. Okay? And I need you. I'm sorry. Aluminum is in group three, so it would be three plus. Okay. Um And so, like I said, these three are all in the same group. So actually, you can all compare them based on size, with the one at the highest in the periodic table, being thes smallest. Okay, so if we go up in the periodic table, this is just group two of the periodic table. Right? Um, so if we go up, this isn't decreasing. Decreasing size, okay. And so that millions, that barium is our biggest. And let's see, magnesium is our smallest, so we already know it's not gonna be this or this. So we know that magnesium is the smallest of the cat ions and group too. Okay, so now it's just a competition between aluminum and magnesium, okay? And so aluminum three plus versus magnesium, cause we already know that the other two are bigger since their lower on the periodic Remember the lower you get on the pyramids, people, mawr, shells, you have right. And so the more shells you have, the bigger the cat eye on. Just because it's bigger, it has more shells that has more electrons. Okay, so we're stuck between aluminum and magnesium. They're actually right Next each other on the periodic table. Okay. Um, so we have aluminum three plus and magnesium two plus. Okay. Actually have the exact same number of electrons. If magnesium lost two electrons and aluminum lost three electrons. They actually have the exact same number of electron. So same number of electrons. Okay, so then how are we gonna figure out? And they have the same number of shells. So how do we figure out who, um is going to be smaller? Well, if you think about it, aluminum has one extra proton compared to magnesium. So aluminum three plus has one more proton. Okay, because it its atomic number is just one more than magnesium. So aluminum has one more proton, yet they have the same number of electrons. Okay, So that means that the nucleus, the nucleus nucleus of aluminum pools, the rest of the electrons, of course, they have other electrons. Right? They lost my knees and lost two electrons and aluminum lost three. But they still have more electrons. So the nucleus of aluminum pulls the electrons closer. The electron cloud closer because it's stronger. Right? Because it has an extra proton remember protons are attracted to electron, so having one more proton means that I can pull that electron cloud closer. So aluminum three plus is actually aluminum. Three plus is the smallest smallest, can I? OK, and so that's how you saw 11 point 10.

University of Maryland - University College
Top Chemistry 102 Educators
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Theodore D.

Carleton College

Allea C.

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University of Kentucky

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