Need help with several pcat questions?

[Atl21]

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1. If an atom's valence electrons are tightly held then we can expect what change in ionization and electron affinity?

2. Why do the elements sodium and chlorine bond so readily? The answer is electron exchange caused by low ionization energy of sodium and low electron affinity of chlorine. Can you explain how?

3. If 1 parent is PpYyRr and the other is Ppyyrr, what is the probability that they will have an offspring that is ppyyRr? What is a fast way of figuring this problem ?

3. Alkene react with acid equal what? Which is nucleophile and which is electrophile? can you give me a brief mechanism? Thanks

 

[fenixtnlfan]

I'll tackle the last two.

#3 Figure out the probabilities for each trait (ex: PpxPp) You can write out the Punnett squares or the best way is to have the probabilities memorized.

So the probability of pp=1/4, yy=1/2, and Rr=1/2. Then you multiply the probabilities together to get 1/16.

#4 For the alkene with an acid, it's gonna depend on the acid you use. Gotta look those ones up. An electrophile wants electrons (loves electrons if you will) and hence is an acid. A nucleophile is the opposite. For a mechanism, you really got to look for websites or use a textbook. I don't think I could type one, but maybe someone else can. I really don't think a mechanism question will be on the PCAT though.

 

[Atl21]

thanks for clearing me up with number 3.. that makes it much easier

 

[fenixtnlfan]

#1 Atom will have a high ionization energy and electron affinity because it doesn't want to give up the electrons. That's my guess.

#2 Sodium's low ionization energy allows the electron to be easily removed and donated to chlorine that has the ability to easily pick up the electron. An easier explanation, sodium and chlorine want to get to noble gas configurations. The easiest way for them to do this is for sodium to lose and electron and chlorine to gain, then them become ions and bond.

 

[fenil2005]

Atl 21 sodium has low ionization energy because it looses electron to get to octet state and chlorine gains an electron to get to octet state. so metals always have low ionization energy and low electronegativity and non metals always have high ionization energy and high electronegativity. hope that will clear everything.......