Fundamentals of Chemistry Question Thread (VCE-level chem)

[PlainElegy]

Hi guys! I was considering posting my questions on the VCE forums for chemistry, but decided not to opt for this since I don't know whether there could be  little bit more in it than VCE chem. Anyway, I have been looking around the forum here, and found mostly questions from students who have done VCE chem...so I hope to start up a thread for those who are doing just foundations for chemistry.

I heard that chemistry is difficult from fellow students who studied it, so I have to admit I'm intimidated. Today was my first day, and I already have quite a few questions. I would appreciate if anyone could help

These are my first questions (these are from the textbook I'm using...and there are no answers at the back of the book)

1. On the basis of their positions in the periodic table, why is it not surprising that ⁹⁰Sr, a dangerous radioactive isotope of strontium, replaces calcium in newly formed bones?

2. In the refining of copper, sizable amounts of silver and gold are recovered, why is this not surprising?

3. Why would you reasonably expect cadmium to be a contaminant in zinc but not in silver?

4. Why is it unlikely that scientists will discover a new element, having an atomic mass of approx 73?

I know there are probably some basic concepts being addressed here, but I don't recall my chem lecturer talk about any possibly related concepts, and the section of the textbook he told us to read did not help...

[hobbitle]

This thread should probably be moved to UoM forum.

Hi fellow CHEM10007-er   I take it you are using the Blackman textbook, I already had the old textbook so I'm using that one for now.  Although your questions are much different to the ones in the Zumdahl text.

All of the questions you asked are really looking for quite broad brush-stroke answers.  Obviously I only had my first lecture today too but it's clear by the questions that they are just asking you to realise that the elements they refer to are generally in the same groups (or related or different in some other significant/obvious way) on the periodic table.

ie. Q1 basically is just that because Sr is the next heaviest Group 2 element to Ca, it has very similar biochemical properties and therefore reactivity to the same things that Ca reacts to. Very similar answers for the rest.

I find Q4 intriguing as I guess it's something about the fact that an element with an atomic mass of 73 would sit between a metal (Germanium) and a non-metal/metalloid (Arsenic)... something about this I suppose makes it 'obvious' as to why we wouldn't discover a new element across this 'bridge'?  Hmmm.

I don't think more detail is expected at this stage although I'd like to know the more detailed answers myself so if anyone here can answer them, that'd be awesome

[nerdgasm]

For Question 4, I think the answer is meant to be based on the idea of what an element actually 'is'. We know that different elements have different atomic numbers (which is just another way of saying they have different numbers of protons in their nuclei).

So, a completely *new* element would have to have a different number of protons to all the other elements that have already been discovered. Flicking through a periodic table, we see that all the elements from 1 proton (Hydrogen) to over 100 protons, and every number in between have already been discovered (even if some of the higher numbered elements are not very stable).

So, a completely new element would require over 100 protons. This, however, would easily push its molar mass over 100 (for the sake of argument, 1 proton weights about the same as 1 neutron, which weighs *about* (not exactly) the same as 1 gram per mol). An element with an atomic mass of around 73 shouldn't have more than a combined total of 73 (or slightly higher) neutrons and protons. But we have just seen that any new element must have at least 100 protons.

Therefore, unless some new type of atom is formed that doesn't need to use protons/neutrons in its nucleus, it's very unlikely we will have a completely new, as yet undiscovered element, of atomic mass 73.

[hobbitle]

For Question 4, I think the answer is meant to be based on the idea of what an element actually 'is'. We know that different elements have different atomic numbers (which is just another way of saying they have different numbers of protons in their nuclei).

Of course - that makes so much more sense.  *facepalm*  I'm new to this ;-)

[PlainElegy]

TY for the replies. I don't remember a thing about chem from pre-VCE days...and I tend to read into things a bit too much.

Are the questions from the Zumdahl text better (more difficult)?

BTW, how do I move this thread to the UoM board? I'm new to this forum.

[hobbitle]

A mod can move the thread if they think it needs to be moved - no biggie.
Welcome to the forum, by the way.
We can even re-title this thread to something like "Fundamentals of Chemistry Question Thread" and use it for all Fundamentals students to post any questions they have throughout the semester.  There aren't many CHEM10007 students on here this semester but there are a LOT of people who know a LOT about Chemistry!
The questions in the Zumdahl seem to be a bit harder earlier on but I haven't done many of them.  I gave in and ordered a second hand copy of the Blackman last night...

[PlainElegy]

Hey Hobittle, do we have to memorize the periodic table? Or do we just need to know what name corresponds to what symbol (or is it an abbreviation? Though I don think so, since we don't end it with full stops)

[hobbitle]

According to the first lecture we need to learn the first 30 elements (full names and symbol).  In previous years students received a copy of the periodic table in the exam, I'm not sure if they have stopped doing this, but it's probably a good thing to learn anyway.

Mick put up some mnemonics to learn them which usually makes it easier in the short term but it's best to learn them rote if you want to put in the extra effort.  If you learn them by mnemonic then you get kind of stuck using the mnemonic every time and questions like "which element has the atomic number of 12?" means you have to recite the first 11 first.  Like if you ask someone "What is the 13th letter of the alphabet" most people can't answer without singing the alphabet song first.

[PlainElegy]

Very true. I also doubted those mnemonics would be of much use in the long term - especially since Mick said that he didn't memorise it that way. I am using association between mental images and the symbols/names...hope it works. How are u going about rote-learning it?

[hobbitle]

I already knew the first 10 from high school.  I am good at connecting sounds so once I have found a 'rhythm' it tends to stick in my head, but I am definitely an aural learner (I listen to the recorded lectures like 3 or 4 times each, but make few notes, except for diagrams).  Saying the elements out loud in order whilst picturing them in the table helps.
Also not stressing too much about it as we will be using the first 20 or so elements so often when we do more stoichiometry and stuff that we will get very familiar with most of them just through use.

[ninwa]

Did you want me to move this thread or...?

[hobbitle]

Did you want me to move this thread or...?

I don't think it matters too much nina.  It'll probably get more exposure where it is now I guess.

[PlainElegy]

Just got out of a confusing tutorial (at least for me). I used to think a pure substance is either made up of one type of element or a compound whose atoms have very strong chemical bonds between them that makes that molecule it's own entity (wrong word usage?). Now I'm not too sure l.

 I was going to check wiki, but remembered that we were advised not to use it.

Speaking of that, does anyone know any good websites for chem?

[hobbitle]

From what I gathered, Pure Substances are either one of two things:
1) Elements (only found on the periodic table)
2) Compounds (made up of two or more elements in the periodic table but are fixed in structure and atomic ratios e.g. CH₄ or H₂O₂)...

As opposed to Mixtures (Homogenous or Heterogenous) which can have variation in the sample depending on a number of factors e.g. who mixed it, under what conditions it was mixed, what measuring instruments were used.

[PlainElegy]

A lot of thanks man! You clarified it really well! Better than the tutor in this case...though I guess I need to give the tutor some credit for being able to get into that kind of role (and all the hard work she would have put in to get there)