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Hi there.
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To write the lewis structure for each of these monotomic ions, i want to start off by looking at the periodic table and talking about the number of valence electrons that the main group elements have.
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So the number of main of valence electrons for the main group elements corresponds to the group number.
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So in group 1a, all of those atoms have one valence electron.
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In group 2a, all of those elements have two valence electrons going over towards the group number.
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Right side, 3a, they all have three valence electrons, 4, 5, 6, 7, and with the exception of helium, the rest of the noble gases have 8 valence electrons.
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All right, we also want to remember that metals lose their valence electrons to form positive ions known as cations.
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Non -metals gain electrons to satisfy the octet rule, and they will form positive ions.
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Form negative ions known as anions.
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Okay, so let's go ahead and get started.
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What i want to start off doing is just writing the lewis structure for the atom, and then we'll write the lewis structure for the ion.
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So starting with chlorine.
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Chlorine is a halogen, so it has an atom as seven valence electrons.
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It's a non -metal, so it is going to gain the necessary electrons to give it eight, to give it an octet.
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So its ion is going to be chlorine with eight dots around it, but since it gained one electron, it's going to have a single negative charge.
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Okay, let's go on to our next one.
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Sodium.
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Sodium is in group 1a, so it has just one valence electron.
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It is a metal, so when it forms an ion, it's going to lose that one valence electron, giving us a sodium ion with a single positive charge.
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Next, we're looking at magnesium.
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Magnesium is also a metal.
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It is in group 2a.
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So it has two valence electrons.
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It's going to lose both of those.
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So we're going to get the magnesium ion with a two positive charge.
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Notice for these positive ions, we're not showing any dots around them, because by losing their valence electrons, all they have left are their core electrons.
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And in a lewis symbol, the core electrons are represented just by the symbol...