<p>Hey all,</p>
<p>I had a few questions as I studied for the AP Chemistry exam, and I'm sure that others on this forum are in a similar dilemma, of sorts. For this reason, I created this thread so that we could bounce questions off of each other. I'll be actively here also.</p>
<p>I had two things that were bugging me:
Why does Mg have the smallest radii out of all of the other elements?
Why is it that Oxygen has a lower ionization energy when compared to Nitrogen?</p>
<ol>
<li>Not sure what you mean… F has the smallest radius than all other atoms.</li>
<li>N has a half-filled p orbital which is more stable than a p-orbital with 4 electrons occupying it as a pair, single, single.</li>
</ol>
<p>Yeah, magnesium doesn’t have the smallest radii. Actually, hydrogen does(I think), but it’s definitely not Mg. And 45daysinrome explained the N ionization energy well.</p>
<p>No, I am sure. This was on our examination for atomic theory. Something about having the smallest ionic radius and that it only relates to the most commonly found ion.</p>
<p>The answer was Mg. I’m positive.</p>
<p>Do you have the question as it was written on the test? I’m just really confused about what you’re asking.</p>
<p>Perhaps Mg was the smallest out of those choices</p>
<p>Smallest radii is Helium because the trend for the periodic table is from left to right for bigger to smaller and from down to up for bigger to smaller. The conceptual explanation: Helium has only one electron shell - 1s. Moreover, the more protons (the higher the atomic number), the stronger the attraction and the attraction is stronger than the force of repulsion between the electron. And the attraction should reduce the size of the atom. In short, helium has the smallest radius.</p>
<p>Oxygen has a lower ionization than Nitrogen because that is where the fourth electron of the 2p4 is added to the first orbital but with a different spin. Remember, according to Hund’s rule, the first three electrons have to fill up the three orbitals of the p subshell individually and with the same spin to achieve the lowest energy. So, note that when the electron changes spin or moves to a different subshell (for example, s to p), the ionization energy decreases, but this is just an usual case, not an always case.</p>
<p>Diagram:</p>
<p>Nitrogen 2p 1 (up) 2 (up) 3 (up) </p>
<p>Oxygen 2p 1 (up, down) 2 (up) 3 (up)</p>
<p>I hope I explain it clearly.</p>
<p>Look below.</p>
<p>Wait, found it online!</p>
<p>[AP</a> Chemistry: Unit 2 Test Review Questions](<a href=“http://www.smes.org/classes/chemistry/ap/aprevquesU2.htm]AP”>http://www.smes.org/classes/chemistry/ap/aprevquesU2.htm)</p>
<p>Use these answers for questions 1-3.</p>
<pre><code> (A) O
</code></pre>
<p>(B) La
(C) Rb
(D) Mg
(E) N</p>
<p>What is the most electronegative element above?</p>
<p>Which element exhibits the greatest number of different oxidation states?</p>
<p>Which of the elements above has the smallest ionic radius for its most commonly found ion?</p>
<p>Multiple Choice Questions:</p>
<p>A</p>
<p>E</p>
<p>D</p>
<ol>
<li><p>O is the most electronegative element in the group because it is near stable. It needs two more electrons. Electronegativity is the ability of an atom to attract electrons when bonded. </p></li>
<li><p>I can only come up with examples to verify this. O can have -1 and -2. Rb would have +1. Mg - +2. La - don’t really know since it is a transition metal. N–2, -3, -4; NO, NH3, and NO2, respectively</p></li>
<li><p>Since it is ionic, Mg would be Mg2+, so its size is smaller since the less electrons mean greater attraction and there’s nothing filling up the 3s orbital.</p></li>
</ol>
<p>Is English your first language? Cuz if not, I can understand why that question confused you…</p>
<p>It’s saying that since Mg2+ has two additional protons and becomes isoelectronic upon losing electrons, it not only loses a shell but also has more attractions to the nucleus. Thus, it gets way small. </p>
<p>O2- is big.
Rb+ is bigger than Mg because it’s lower on the table.
N3- is big.</p>
<p>That’s why its -ion- is the smallest OF THE CHOICES. It doesn’t mean of ALL elements. Just of the choices given.</p>
<p>
Mg2+ means that it lost two electrons. An atom cannot gain or lose protons. Only electrons can be gained or removed. But everything else is correct.</p>
<p>I know that. I really sincerely know that. I don’t think I’ve ever had a flub that bad in my life XD</p>
<p>Haha…if Mg gained two protons, we’d be dealing with some sort of silly nuclear chem :P</p>
<p>Yeah, basically N, O, and Mg ions will have the same number of electrons, but Mg has the most protons so the electrons are attracted more so the radius is smaller.</p>
<p>OP is a SCAMMER, this is unrelated but do not send him any tests or test materials of any kind, you won’t hear from him again.</p>
<p>Does anybody know how much of the multiple choice and the free response you have to get right in order to get a 5 on the exam?</p>
<p>AP Chemistry
MC*1.066667,</p>
<p>5 is 107-160 (out of 160 maximum)
4 is 85-106
3 is 61-84
2 is 42-60
1 is 0-41</p>
<p>FRQ</p>
<h1>1 20%</h1>
<h1>2 20%</h1>
<h1>3 20%</h1>
<h1>4 10%</h1>
<h1>5 15%</h1>
<h1>6 15%</h1>
<p>(1+2+3)*1.71428</p>
<p>4*.5333333</p>
<p>5,6*1.5</p>