prelim stuff (1 Viewer)

[velox]

im a bit confused on what these dot points r askin, i get the idea but i dont know what to put down for them...

Identify that matter is made of particles that are continuously moving and interacting

Identify the differences between physical and chemical change in terms of rearrangement of particles

Apply the Periodic Table to predict the ions formed by atoms of metals and non-metals

thanks!!!

 

[Calculon]

Originally posted by wrx
im a bit confused on what these dot points r askin, i get the idea but i dont know what to put down for them...

Identify that matter is made of particles that are continuously moving and interacting

I think that maybe thats referring to the particle theory, the one where gases have fast moving particles asnd solids have very slowly vibrating particles

Originally posted by wrx
Identify the differences between physical and chemical change in terms of rearrangement of particles

A physical change involves a change outside of the molecule, for example intermolecular forces are broken and a change of state is the result eg solid -> liquid. Chemical changes involve rearranging the molecule or breaking it up

Originally posted by wrx
Apply the Periodic Table to predict the ions formed by atoms of metals and non-metals

I seriously dont know about that one. Maybe it has something to do with electronegativity and how a metal/non-metal compound usually forms a crystalline lattice which breaks up into ions in solution. Or more likely it has something to do with valency, as in there may be twice as many metal ions as non metal ions depending on the group in the periodic table
Hope that helped

 

[04er]

Or more likely it has something to do with valency, as in there may be twice as many metal ions as non metal ions depending on the group in the periodic table
Hope that helped [/B]

I agree, it simply refers to your understanding of Group numbers in the periodic table. You should be familiar with how the position of a certain element (in terms of group number) relates to the valency on the ion formed.

 

[velox]

o kool thanks for that! Sorry i got some more questions....
Identify differences between physical and chemical properties of elements, compounds and mixtures

and also Can u thermally decompose a covalently bonded compound??

 

[Calculon]

Physical properties are things such as is it flexible or brittle, hard or soft, does it conduct electricity(from memory)
Chemical properties are how electronegative it is how reactive it is, what elements are in it etc. Please feel free to correct me cos I'm not 100% sure


And im pretty sure you can decompose a covalently bonded compound by heat, but again not 100% sure
EDIT: I was wrong, you cant because covalent bonds are inside the molecules

 

[velox]

thanks, ill see what cm_tutor says about it

 

[CM_Tutor]

Originally posted by wrx
Identify that matter is made of particles that are continuously moving and interacting

I agree with Calculon that this refers to the aspects of particle theory to which he referred, but it also refers more generally to the need for you to accept the existence of atoms as a basic building block of everything chemical. Without atoms, the rest of the syllabus is pretty pointless, and it is a notion with which many peoplr struggle.

Identify the differences between physical and chemical change in terms of rearrangement of particles

Building on what Calculon has said, the easiest way to distinguish them (in a practical sense) is to look for two things:

1. Is there any evidence of a new substance being formed? (this would imply a chemical change)

2. Can this be easily reversed by some simply physical means? (this would imply a physical change).

Take, for example, burning toast. There is a wealth of evidence for a new substance - you can see black stuff that wasn't there, there has been a notable change in texture, there is an odour that wasn't present before. Also, there is no viable way to undo this process. Thus, chemical change.

Now, how about boiling water for the coffee to go with your burnt toast? Well, here we have a physical change - I can cool the steam to recondense any water that boiled, and all the water did was get hot - no new substance in sight, easily reversed by physical means (cooling), thus physical change.

Uh oh, the milk for your coffee has gone sour. That's definitely another chemical change - can't readily undo, and there is plenty of evidence for a new substance - gluggy / chunky bits, smell, appearance (now has two phases, one clear, the other not), etc.

Apply the Periodic Table to predict the ions formed by atoms of metals and non-metals

This one is definitely about valency. It's applying the PT to predict that sodium forms Na⁺ ions, and chlorine forms Cl^- ions, etc.

Originally posted by Calculon
Physical properties are things such as is it flexible or brittle, hard or soft, does it conduct electricity(from memory)
Chemical properties are how electronegative it is how reactive it is, what elements are in it etc. Please feel free to correct me cos I'm not 100% sure

No problem here, but I would add MP and BP to the list of physical properties, as they are two of the most common physical properties discussed.

And im pretty sure you can decompose a covalently bonded compound by heat, but again not 100% sure

Yes, you can

EDIT: I was wrong, you cant because covalent bonds are inside the molecules

No, you were right originally. What made you change your mind?

 

[velox]

but where it say about "in terms of rearrangement of particles" ur answer doesnt state anything to do with that...am i lost or is something missing?

 

[CM_Tutor]

Sorry, I was building on what Calculon had already said

Originally posted by Calculon
A physical change involves a change outside of the molecule, for example intermolecular forces are broken and a change of state is the result eg solid -> liquid. Chemical changes involve rearranging the molecule or breaking it up

So, for example, boiling water involves the separation of particles (water molecules) from one another, but not any change in the nature / composition of those particles. Burning toast involves changes in the composition of the particles (molecules) that make up the bread, in order for new particles (of the black stuff) to be formed.

My post was really aimed more at a useful way of recognising chemical and physical changes, as questions often involve classifying something as a chemical or physical change, so no explanation is needed. Also, in a lab you want to look for evidence that a chemical chnage has occurred, and this is how it is done.

Hope this clears up what I meant, and ask again if it's still not clear.

 

[velox]

ah ic thanks heaps

 

[Calculon]

Originally posted by CM_Tutor

No, you were right originally. What made you change your mind?

I was thinking that a chemical change cannot be induced by physical means with out some other chemical being present eg oxygen in combustion
Covalent bonds are the ones inside molecules right?

 

[velox]

think so.....

btw what is a nucleon?

 

[Xayma]

A nucleon is a sub-atomic particle that is in the nucleus, ie nuetrons and protons are nucleons

 

[gershy]

Be careful with covalent bonds. Sure they hold the atoms together in molecules such as H2O, CO2 etc, but they also hold the network together in diamond, SiO2, SiC and within the layers of graphite.

 

[xiao1985]

Originally posted by gershy
Be careful with covalent bonds. Sure they hold the atoms together in molecules such as H2O, CO2 etc, but they also hold the network together in diamond, SiO2, SiC and within the layers of graphite.

yes, covalent molecular (also coordinate covalent) and covalent network...

 

[velox]

thanks pplz another question...
Name the following:
Na2S203.5H20
in the answer it says Sodium Thiosulfate Pentahydrate

Where does the thio some from?
Also how do u know when to add the Mono, Di, Tri etc to a formula?

 

[CM_Tutor]

Originally posted by Calculon
I was thinking that a chemical change cannot be induced by physical means with out some other chemical being present eg oxygen in combustion
Covalent bonds are the ones inside molecules right?

Taking the second point first, yes covalent bonds occur in molecules, but they also occur in other places, like between atoms in network covalent structures, and between atoms within polyatomic ions - ie the sulfur-oxygen bonds in the sulfate ion, SO₄^2-, are covalent.

As for the first bit, there are many reactions in which heat is used to cause a chemical change to occur, and such chnages often involve breaking / forming covalent bonds - consider the process of cooking a steak, for example, or roasting meat in an oven.

As for some more chemical examples, radical initiators used in addition polymerisations are often formed by heating, such as:

C₆H₅-C(=O)-O-O-C(=O)-C₆H₅ ---heat---> 2C₆H₅COO

(Note the product here has only 7 electrons on the final O)

or

CH₃-C(CN)₂-N=N-C(CN)₂-CH₃ ---heat---> 2CH₃C(CN)₂ + N₂

Again, one product here is a radical - that is, it has an unpaired electron.

A simpler example, thermal decomposition of lead(II) nitrate involves breaking covalent bonds within the nitrate anion:

2Pb(NO₃)_{2 (s)} ---heat---> 2PbO_(s) + 4NO_{2 (g)} + O_{2 (g)}

 

[CM_Tutor]

Wrx, the prefix "thio" means change an O to an S.

So, since sulfate = SO₄^2-, it follows that thiosulfate = S₂O₃^2-

Similarly, cyanate = CNO^- and so thiocyanate = CNS^-

And even: Since ethanol = CH₃CH₂OH, ethanethiol = CH₃CH₂SH

Thus, Na₂S₂O₃.5H₂O is sodium thiosulfate-5-water or sodium thiosulfate pentahydrate.

 

[velox]

Sorry, i still dont understand, about how we get the S203 from the
SO4, if we change the 0 to an S dont we get SS4, im lost

 

[CM_Tutor]

Sorry, I meant "thio" means change ONE O to an S, not all of them.