Help Required!

[ChemSiddiqui]

Hi, well i have a few questions to ask so i will number them up.

 

1.

 

'The gaseous oxides of nitrogen have positive enthalphy changes of formation.

 

which factors are most likely to make the most significant contribution to these enthalphy changes?'

 

2.

 

' There was this question in exam which had 3 options and all three,first and second, second and third or the first only is correct. The question gave a table as.

 

Element X C Si Ge

 

bond length X-X/nm 0.154 0.234 0.244

 

the question was:

 

Why does the bond length increase down the group?

 

the options were:

 

1. Orbital overlap decreases down the group

 

2. Atomic radius increases down the group

 

3. Nuclear charge increases down the group

 

Now i believe the 2 option is definately correct and 3 is wrong. But i am uncertain about the first.'

 

Please do let me know what you think for an answer with some easy explainations. Your help will be most appreciated.

[chemhero]

For part Two of your enquiry:

 

I think the first is right; as we go down the group, the orbitals are more diffuse - there is less chance of finding an electron in an overlapping "bonding" region. This then coincides with atomic radius, so yea, option 2 is right like you say. Option three...well, it has something to do with bonding, but nothing that fits in here.

 

 

Have fun,

 

Matt