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## GR0877 Problem 96

PROBLEM STATEMENT: This problem is still being typed.

SOLUTION: (D) If you impure into tetravalent germanium atom $Ge$ a pentavalent element such as $As$, $P$, $Sb$ or $N$, then four of the five valence electrons introduced by impurity atoms come into contact with four neighboring atoms of $Ge$ and form a stable shell of eight electrons, while the fifth electron will be weakly bound to the nucleus of the impurity atom. This creates an excess of negative ($n$-type) electron charge carriers. The only element that cannot be used to create an excess of negative charge is $B$, since it has only three valence electrons.

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Categories: 0877 Tags: , , , ,
1. 07.10.2012 at 06:31

I thought this problem was ridiculous. It was trivia. Who the heck knows the periodic table well enough off the top of their head to know that germanium is a type IV element and that the others are IV or V respectively?

2. 07.10.2012 at 06:33

I suppose that you technically don’t need to know that Ge is type IV, but you would have to know that boron is type III and the others are not (and therefore boron stands alone) – which is still trivia, and still ridiculous.

• 16.10.2013 at 21:52

agreed.

3. 18.10.2013 at 06:48

I agree it’s ridiculous that they test this, but the good news is that you only actually need to know the second and third rows of the periodic table. If you can memorize those, you can see that N and P are in the fifth column and B is in the third. If you understand how doping works, it’s clear that regardless what the other choices are, B must be the odd one out.

Of course this still means memorizing two rows. It’s not fun, but a good mnemonic helps. The dumb, nonsensical one I came up with is “Libe Bacon of Ne! Nah Mang, Al Sips Chlorine.” This translates to the elements like so: “LiBe BCN OF Ne! Na Mg, Al SiPS ClAr(ine).” It rhymes, and almost has a sense of grammar. Works for me, so thought I’d share.