chem prelim (1 Viewer)

[bubblesss]

chem again!!!!!

covalent compounds are formed when two non-metals combine. beryllium is a metal and fluorine is a non-metal then how does beryllium fluoride BeF2 become a covalent compound?

 

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Re: chem help guys!!!!!!!

Ah my bad, cbf writing the units and balancing it through typing... So what was the flaw with my actual calculation? Is your answer correct?

 

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Re: chem again!!!!!

BeF2 is an ionic compound, not a covalent compound. (Metal + Non-metal)

 

[minijumbuk]

Re: chem help guys!!!!!!!

Yes, I'm pretty certain my answer is correct.

The flaw of your actual calculation is the molar mass bit. I have no idea how you got 310. The molar mass of Ag is clearly 107.9, or 108.

You probably used the molar mass of silver sulphate. But we're not interested in the mass of silver sulphate, only the mass of silver ions

 

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Re: chem help guys!!!!!!!

Ah, I found the molar mass of Ag2SO4, rather than finding the molar mass of silver and multiplying by 2. Now I've realised I need more work with my calculations.

Thanks.

 

[minijumbuk]

Re: chem help guys!!!!!!!

Ah, I found the molar mass of Ag2SO4, rather than finding the molar mass of silver and multiplying by 2. Now I've realised I need more work with my calculations.

Thanks.

No, you don't multiply the molar mass of silver by 2. You've already got the number of moles of Ag ions. All you need to do is multiply it by Ag's molar mass.

 

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Re: chem help guys!!!!!!!

Sorry, I meant multiplying the moles of silver ions by 2 (2x10-6 mol Ag+), then finding the molar mass of silver through the periodic table, and finally, calculating the mass through the calculation.

 

[minijumbuk]

Re: chem again!!!!!

It's a special case. Don't worry about it.

 

[minijumbuk]

Re: chem help guys!!!!!!!

Sorry, I meant multiplying the moles of silver ions by 2 (2x10-6 mol Ag+), then finding the molar mass of silver through the periodic table, and finally, calculating the mass through the calculation.

:uhhuh::uhhuh::uhhuh:

 

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Re: chem again!!!!!

Ah those special cases...never knew it could be covalent though...

 

[minijumbuk]

Re: chem again!!!!!

It's not really covalent. If you're interested, search for beryllium fluoride on wikipedia.

 

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Re: chem again!!!!!

It's not really covalent. If you're interested, search for beryllium fluoride on wikipedia.

http://en.wikipedia.org/wiki/Beryllium_fluoride

I did. It didn't really state specifically whether it was ionic or covalent.

Beryllium fluoride is the chemical compound with the formula BeF2. It is the binary beryllium compound with the greatest amount of ionic character (due to the high electronegativity of fluorine), but even so it is not considered ionic by many chemists.

 

[bubblesss]

Re: chem again!!!!!

thanks so its a special case but is it considerd as ionic or covalent??

 

[minijumbuk]

Re: chem again!!!!!

http://en.wikipedia.org/wiki/Beryllium_fluoride

I did. It didn't really state specifically whether it was ionic or covalent.

Probably has properties of both. Like the quantum theory. Is light wave or particle?

 

[Continuum]

Re: chem again!!!!!

thanks so its a special case but is it considerd as ionic or covalent??

It's considered covalent. If you looked at the electronegativity difference however, you would assume it's ionic because the different is greater than 2 (should be, though I didn't check). However, Be is a special atom because it doesn't obey the octet rule (B is the other one).

Be can only ever reach 4 electrons in its outer shell. In sharing electrons with the 2 F atoms, it reaches that 4 electrons. Since F also thinks it has that extra electron needed to reach a stable electron configuration, it too is happy with the organisation of electrons in BeF₂. Thus, the compound can exist.

 

[bubblesss]

Re: chem again!!!!!

thanks a lot. now i get it. damn these exceptions in chemistry.

 

[Continuum]

Re: chem again!!!!!

No problem.

 

[bubblesss]

chem prac

anyone have any past chem prac papers for practice. any help is appreciated.:uhhuh: :uhhuh: :uhhuh: :uhhuh: :uhhuh: :uhhuh:

 

[bubblesss]

Re: chem again!!!!!

how does boron become an exception? isn't it just a non-metal?

 

[minijumbuk]

Re: chem again!!!!!

how does boron become an exception? isn't it just a non-metal?

It's actually a semi-metal.
I'm not sure HOW, but yes, Boron does form weird bondings.