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Simple Chemistry question [new question, 11pm EST]
urahonky
Cynical Old ManRegistered User regular
Cynical Old ManRegistered User regular
I'm working on a practice exam. I've got the answers to the practice but this one doesn't make sense:
Which of the following substances might be ionic?
a. HCl
b. NaCl
c. CH3Cl
d. NCl3
e. H2O
Now the answer is b, and the book says stuff about the cation and anions. Which says Na is +, and Cl is -. But what about HCl? Is Hydrogen that one "exception" to the rule? I thought H was +, so HCl should form the same ionic bond, right?
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I'm stuck on another. I can't seem to find any information about this in the book or his slides, but he's got it on the practice exam. This makes me worry.
It says:
The predicted product of the reaction of Li and N2 is:
a. LiN
b. Li2N
c. Li3N
d. Li2N2
e. Li2N3
The answer is C, but I don't know why. I N has -3 charge, and Li has +1. Which means you need 3 Li to make it balance with N... But how do you go from N2 to nothing?
I'm worried about this one because there are 4 of these questions in a row. The next one makes less sense to me, since one is a transition metal.
The predicted product of the reaction of Al and O2 is: Al2O3 How does that make sense??
Which of the following substances might be ionic?
a. HCl
b. NaCl
c. CH3Cl
d. NCl3
e. H2O
Now the answer is b, and the book says stuff about the cation and anions. Which says Na is +, and Cl is -. But what about HCl? Is Hydrogen that one "exception" to the rule? I thought H was +, so HCl should form the same ionic bond, right?
=======================
I'm stuck on another. I can't seem to find any information about this in the book or his slides, but he's got it on the practice exam. This makes me worry.
It says:
The predicted product of the reaction of Li and N2 is:
a. LiN
b. Li2N
c. Li3N
d. Li2N2
e. Li2N3
The answer is C, but I don't know why. I N has -3 charge, and Li has +1. Which means you need 3 Li to make it balance with N... But how do you go from N2 to nothing?
I'm worried about this one because there are 4 of these questions in a row. The next one makes less sense to me, since one is a transition metal.
The predicted product of the reaction of Al and O2 is: Al2O3 How does that make sense??
urahonky on
0
Posts
But each type of atom has an "electronegativity" value, and you can use these to figure out if a compound will be ionic or will have covalent bonds.
Since I've forgotten how I'm searching google so I can maybe give you better advice.
You can find tables with electronegativity values pretty easily. Also the actual link has diagrams and stuff to explain it better.
Does this make it any easier or is this total gibberish to you? Seems like unless you have been taught to memorize if certain compounds are ionic or not, you should at least have heard of this before.
"Ionic bonds occur between a metal and non-metal." Which would make HCl wrong. I guess that's the easiest way to tell?
And honestly, based on the amount of chem I have taken in my life, albeit like ~5+ years ago, I should know the answer for sure but... i would think HCl would be ionic as well, but it might be because its an acid and there is some funky stuff that goes along with that which makes it not ionic. Or not as ionic.
However NaCl would be MORE ionic, so would be the correct answer to the question.
I could give you a brief explanation, if you want.
I hate gen-ed classes so much.
Edit: If you were to write the chemical equation it would be 6Li +N2 -> 2Li3N
It says N2 because the molecular form of pure nitrogen is N2. So: N2. If you want to be picky and balance both sides, it would be 2 Li3N.
Aluminum oxide is a tricky one. At a gen-ed level you might be able to get away with waving your hands and saying that aluminium is a cation with +3 charge and oxygen an anion with -2 charge and therefore we have an ionic bond of 4Al + 3O2 -> 2 Al2O3. But technically speaking this is wholly wrong and aluminum oxide has a strongly covalent character.
Lithium and nitrogen can be balanced with +3 and -3.
It's basically a big game of making both sides add up to a whole number at this level. :P Find the lowest common multiple of the two charges.
http://zebu.uoregon.edu/~imamura/122/images/periodic_table.gif
Al looks very light blue, are those special cases? I can't seem to find a name other than "metals".
If that's wrong I apologize - I just have most of the common metals memorized (Zn2+, Fe 2+/3+, etc.)
Think about it like this. Consider this table: the periodic table stretched out. You can see that the lathanides and actinides which are usually pulled out to a lower section are analagous to the transition metals for the higher periods. Likewise, you can imagine also removing the transition groups to form a periodic table that might look like this in the first three periods:
At this point we handwave a lot and say that aluminum can be counted from the left (so to speak) which suggests a +3 charge.
Further down the periodic table the metals do indeed start becoming weirder; aluminum itself does have +1 and +2 oxidation states (for that matter, even sodium and magnesium have a number of oxidation states). But +3 is the most stable one. The first few periods tend to have simpler behaviors.
Now if the atoms are all on the rightside of the periodic table, chances are it's a valence bond (electrons are shared evenly), but if it's a mix between left and right the sharing it's probably an ionic bond (the electrons are shared unevenly).
Hydrogen is a special case, because in this (very simplified) explanation, it can lose or gain 1 electron to bond either way (And can thus be both ionic or valence very easily).
Deep down the periodic table these rules tend to break down a bit.