Bonding of halogens in different states

Doing A level Prep, not doing well. How come Cl2(g) is covalent and Cl2(aq) is ionic but Br2(g) is covalent and stays covalent when in an aqueous state? Does it have to do with reactivity? Is it easier to ionize because there is less electron shielding? Am I asking too many unnecessary questions?

Reply 1

EierVonSatan

Original post by Tzoky

Honestly, the best prep you could be doing is revising your GCSE content :yes:

Both bromine and chlorine are diatomic molecules held together by s single covalent bond; this is true regardless of whether they are in the gas or aqueous phases. I think the difference that you are alluding to is that the chlorine reacts with the water in the following way:

Cl₂ + H₂O ⇌ HCl + HOCl

The HOCl can then partly dissociate into ions (which are 'bonded' to other water molecules through a type of intermolecular force). Bromine does the same thing but to a lesser extent...in other words it's shifted more to the left of the reversible reaction.

I hope that helps.

(edited 2 years ago)

Reply 2

Tzoky

That honestly makes more sense, thank you. You have a good day :smile:

Reply 3

scimus63

google disproportionation reactions. This is something new in A-level but its simple to get. Chlorine and bromine both reaction with water in a disproportionation reaction.

Make sure you know what oxidation, reduction , equilibrium and difference between weak and strong acids is from your gcse course before looking at these disproportionation reactions are.

Reply 4

EierVonSatan

Original post by scimus63

Disproportionation reactions are not new to A-level :tongue:

and you don't really learn about strong and weak acids at GCSE :no:

Reply 5

Youareloved111

Original post by EierVonSatan

Disproportionation reactions are not new to A-level :tongue:

and you don't really learn about strong and weak acids at GCSE :no:

i think it might depend on the course cos I learnt about strong and weak acids

Reply 6

EierVonSatan

Original post by Youareloved111

i think it might depend on the course cos I learnt about strong and weak acids

which exam board?

Reply 7

scimus63

Its new to a gcse students, disproportionation reactions are usually covered in year 12! Weak and strong acids are in the gcse chemistry triple award- check the specification.

Reply 8

scimus63

Copied this from GCSE aqa TRILOGY SPEC!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

4.4.2.6 Strong and weak acids (HT only)
Content Key opportunities for
skills development
A strong acid is completely ionised in aqueous solution. Examples
of strong acids are hydrochloric, nitric and sulfuric acids.
A weak acid is only partially ionised in aqueous solution. Examples
of weak acids are ethanoic, citric and carbonic acids.
For a given concentration of aqueous solutions, the stronger an
acid, the lower the pH.
As the pH decreases by one unit, the hydrogen ion concentration of
the solution increases by a factor of 10.
Students should be able to:
• use and explain the terms dilute and concentrated (in terms of
amount of substance), and weak and strong (in terms of the
degree of ionisation) in relation to acids

Reply 9

EierVonSatan

Original post by scimus63

Fair enough I am surprised, I've never seen it on a GCSE spec before and I've taught a few.

Reply 10

scimus63

Here is OCR- maybe you read the specification if you are actually teaching it.

C3.3g
Use and explain the terms dilute and concentrated (amount of substance) and weak and strong
(degree of ionisation) in relation to acids