Sciencemadness Discussion Board

Very basic formula questons

NEMO-Chemistry - 14-8-2016 at 06:59

I was going to fit this on the end of my other thread, but i feel its different enough to go on its own.

I do have a couple of basic text books on chemistry as used in the older UK GCSE chemistry course. While the books cover alot of the basics i have found gaps where it is like you are just meant to 'know'!

Maybe some of the most basic questions and knowledge are things that get taught in a classroom, i dont know.

So please feel utterly free not to waste your time with these questions, i have searched and i am reading, but some of the very basic questions dont seem to be answered.

I am working from what i think is a reasonable periodic table here

http://www.ptable.com/#Compound/H+N+O

I like the layout and amount of information contained in a uncluttered way.

I am using various websites such as wiki how to and Bitesize amongst others. While trying to learn how a formula is arrived at i picked a few common chemicals i know the formula of, i then used the periodic table to verify why the formula is what it is.

This is where i came a cropper on one in particular!

I know Nitric Acid is HNO3

My limited understanding says the formula is arrived at because H has an Atomic number of 1 and a valence? of 1+

Nitrogen being a non metal and having an atomic number of 7 has a valence of -1.

Therefore they cancel out and you dont use 1's in formula, this is all understandable and fits with what i could get from the periodic table, the bit i dont get is the O3.

Oxygen has an atomic number of 8 its a non metal in the second row, so has a shell of 2 and 6 electrons.

From what i have read this would suggest a valence of -2?? So how come its actually 3?

I am sorry if the question isnt very clear, i am trying to work out how common formula are arrived at, to be honest i am sick of writing things on here in words simply because i cant work out the formula!!

Non of the sites i am using explain how HNO3 actually has O3 in it, if you see what i mean!

If anyone knows a better site than those i am using or even a book that starts at numpty onwards i would appreciate it. I have looked at the dummies guide to chemistry site (from the book), and to be honest its pretty bad at alot of the basics.

I am not completely stupid, i can read and understand alot of it, but some of the very basics just dont seem to be completely covered. I do appreciate this is likely the kind of thing a class would cover and that is probably why i am not finding the most basic info.


If anyone answers (dont blame you if you dont), then i will post any other periodic/equation questions i come across in here.

Regards
NEMO

NEMO-Chemistry - 14-8-2016 at 08:00

Ok got the answer! But to be fair i feel totally cheated!! Acid's have H in them, so Nitric acid is H and based (wrong term but all i could of) on Nitrate, Nitrate is NO3. So this makes Nitric Acid HNO3.

But nowhere is this explained! and why is Nitrate NO3?

Why do You need 3 Oxygens to the Nitrogen?

The harder stuff seems easier than the so called basic beginnings!

I will get there, but the first bits are not intuitive.

Magpie - 14-8-2016 at 08:07

Nitrogen has a valence of +5 in HNO3. Valences are, in general, not fixed to one number but can vary with the situation.

Your textbooks must not be very good. This subject should be well covered in an elementary chemistry textbook, like the one by Linus Pauling, "General Chemistry."

Zandins - 14-8-2016 at 08:11

First, one should not confuse "valency" and "oxidation number". Valency is simply the number of chemical bonds formed by an atom. For instance, hydrogen always has a valence of 1, and oxygen (almost) always has 2. However, for most elements, there are several possible valencies, which complicates things. Therefore, it is worth thinking in terms of "oxidation number".
The oxidation numbers of all atoms in a molecule must sum to 0. Hydrogen is defined as having an oxidation number of +1, except in alkali metal hydrides (NaH, RbH). Oxygen has an oxidation number of -2, except in peroxides. These simple rules allow us to calculate the oxidation number of nitrogen in nitric acid.
0 = 1+(-2)*3+x <==> x =5
Therefore, the oxidation number of nitrogen here is 5, not -1.

blogfast25 - 14-8-2016 at 08:12

Quote: Originally posted by NEMO-Chemistry  


But nowhere is this explained! and why is Nitrate NO3?

Why do You need 3 Oxygens to the Nitrogen?

The harder stuff seems easier than the so called basic beginnings!



It's NO3-, actually.

You should start by studying the concept of Oxidation State, really. And forget about nitric acid for a minute, it's a fairly non-typical case, not something where you want to start your learning curve.

Have a good look at this, e.g.:

http://www.chemguide.co.uk/atoms/bondingmenu.html#top

Also, this 'in house' resource on chemical bonding and why molecules are the way they are:

http://www.sciencemadness.org/talk/viewthread.php?tid=62973&...

[Edited on 14-8-2016 by blogfast25]

NEMO-Chemistry - 14-8-2016 at 08:22

Thanks guys, % for nitrogen fits with what i see on the PT, so 3 for Oxygen makes sense!

Regarding the books i have, I am using the previous course work books for UK GCSE exams in secondary schools. I wrongly assumed if the books were used to teach a secondary school exam course, then the book would be suitable.

I will grab the book you mention.

Thanks Blogfast, i now have a start point on what to study.

Just for info the books are part of the OCR GCSE range of standard chemistry text for teaching secondary level chemistry. No wonder they changed the course 2 years ago!

NEMO-Chemistry - 14-8-2016 at 11:24

Blogfast25 i will be delving into your inhouse resource once i have the baby steps taken care of. I did have a long mooch through it and its excellent, but at the moment out of my league!

Took ages to find a copy of linus pauling, i hope i have the right one! If its good i will track down a second hand paper copy from Abe books. I tend to use pdf books first and then the really good ones i buy for my shelf :D.

I have vogel 3rd but on the hunt for a cheap 5th copy. They always turn up now and then, its a case of keeping an eye out for them. My town has a very old obscure second hand bookshop, the lady that owns it is as mad as a box of frogs but very helpful.

She has a list i gave her with rough prices of what i would pay, she looks out for ex library books for me as these apparently sell cheaper because people hate library stamps in books!

Magpie - 14-8-2016 at 12:23

I actually never used the Pauling book in school but picked it up much later at a used book sale. It takes a somewhat different and deeper look than most beginning texts, and as he says in the introduction is meant for chemistry majors and other science majors.

A good US text that I can recommend that is a little more modern than Pauling is that by Holtzclaw et al, "College Chemistry." Certain editions have a complete section on qualitative analysis, which makes them especially valuable. I have the 7th ed with QA.

NEMO-Chemistry - 14-8-2016 at 12:53

Quote: Originally posted by Magpie  
I actually never used the Pauling book in school but picked it up much later at a used book sale. It takes a somewhat different and deeper look than most beginning texts, and as he says in the introduction is meant for chemistry majors and other science majors.

A good US text that I can recommend that is a little more modern than Pauling is that by Holtzclaw et al, "College Chemistry." Certain editions have a complete section on qualitative analysis, which makes them especially valuable. I have the 7th ed with QA.


I will hunt it down thanks!

blogfast25 - 14-8-2016 at 12:55

Quote: Originally posted by NEMO-Chemistry  
Blogfast25 i will be delving into your inhouse resource once i have the baby steps taken care of. I did have a long mooch through it and its excellent, but at the moment out of my league!



Always glad to see a 'newbie' willing to start where we all started: in the study! :)