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Help with some structure & bonding questions!

Hi there,

I've got some homework which I am quite struggling with about structure & bonding (AS Level). I've done most of the questions but there are some questions which are puzzling me and any help & assistance would be greatly appreciated!

1) Why does hydrogen iodide require more heat energy for melting than hydrogen chloride does?


2) Why is the heat energy needed to vaporise one mole of sodium chloride (171 kJ mol-1) is much greater than the heat energy required to melt one mole of sodium chloride?


3) When aluminium chlordie reacts with chloride ions, as shown by the equation below, a co-ordinate bond is formed...
AlCl3 + Cl- ==> AlCl4-
Explain how this co-ordinate bond is formed.


Any help would be greatly appreciated thanks! :smile:
Reply 1
Avatar for Charzhino
Charzhino
19
1) Iodide has a larger atomic radii so increased van der waal's force interactions between it and H.

2) Is that vaporise from solid or from liquid phase?

3) Co-ordinate bond is where both pairs of bonding electrons come from the same souurce, i.e/ aluminium
Reply 2
Avatar for PJ Chemnerd
PJ Chemnerd
1) HI is ioniclly bonded, while HCN is covalently bonded, intermolecular forces, etc
2) more heat energy required to vapourise NaCl than just melt it, breaknig bonds,etc
3) is a co-ordinate bond the same a dative bond?? if not i have no idea
Reply 3
Avatar for PJ Chemnerd
PJ Chemnerd
HI isnt ionically bonded oops, mindblank 4 a second, its possibly due to the higher electronegativity/polarity of the H-I bond compared to H-C bond-greater intermolecular forces in HI than HCN
Reply 4
Avatar for shengoc
shengoc
12
alex91
Hi there,

I've got some homework which I am quite struggling with about structure & bonding (AS Level). I've done most of the questions but there are some questions which are puzzling me and any help & assistance would be greatly appreciated!

1) Why does hydrogen iodide require more heat energy for melting than hydrogen chloride does?This would simply imply the intermolecular force in HI is stronger than HCl, and this is attributed to the higher van der Waals in HI, iodine has got more electrons for van der waals interaction.


2) Why is the heat energy needed to vaporise one mole of sodium chloride (171 kJ mol-1) is much greater than the heat energy required to melt one mole of sodium chloride?


3) When aluminium chlordie reacts with chloride ions, as shown by the equation below, a co-ordinate bond is formed...
AlCl3 + Cl- ==> AlCl4-
Explain how this co-ordinate bond is formed.
Aluminium does not have a full p orbital. even in AlCl3,i it still has one more unfilled p orbital, and this is where the Cl- with an extra electron can form a dative covalent fair(or co-ordinate bond) with this empty orbital. The structure rearrange itself to form AlCl4-, which is tetrahedral as Al has no lone pair remaining.


Any help would be greatly appreciated thanks! :smile:


The red coloured is my answer, could be wrong about them though.
Reply 5
Avatar for Gerererer
Gerererer
1
http://www.a-levelchemistry.co.uk/AQA%20AS%20Chemistry/Unit%201/1.3%20Bonding/1.3%20home.htm


the answers are on here.... if that helps :wink: (i got stuck as well and after looking on here i decided to Google the mark scheme.. xD)
Original post by alex91
Hi there,

I've got some homework which I am quite struggling with about structure & bonding (AS Level). I've done most of the questions but there are some questions which are puzzling me and any help & assistance would be greatly appreciated!

1) Why does hydrogen iodide require more heat energy for melting than hydrogen chloride does?


2) Why is the heat energy needed to vaporise one mole of sodium chloride (171 kJ mol-1) is much greater than the heat energy required to melt one mole of sodium chloride?


3) When aluminium chlordie reacts with chloride ions, as shown by the equation below, a co-ordinate bond is formed...
AlCl3 + Cl- ==> AlCl4-
Explain how this co-ordinate bond is formed.


Any help would be greatly appreciated thanks! :smile:


1) Watch some Naruto

2) Watch some Attack on Titan

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