Dative Covalent Bonding in BCl3?

Watch this thread
DoubleJazzy
Badges: 4
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#1
Report Thread starter 9 months ago
#1
Recently I answered an exam style question which asked me to draw a dot and cross diagram for BCl3, showing outer electrons only.

The actual answer showed a boron atom in the centre, with 3 covalent bond electron pairs surrounding it from each chlorine atom.

Following the octet rule, I drew an extra two electrons from one of the chlorine atoms to signify a dative covalent bond, however this seems to be incorrect.

Why is it incorrect, and in what situation would I use dative covalent bonding?

James
0
reply
Dylan8421
Badges: 10
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#2
Report 9 months ago
#2
Dative covalent bonding is when both electrons in the covalent bond come from the same atom.

As boron has 3 electrons in its outer shell it can form 3 covalent bonds with each chlorine where each atom donates 1 electron to the bond so each chlorine can gain a full outer shell.
Last edited by Dylan8421; 9 months ago
0
reply
DoubleJazzy
Badges: 4
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#3
Report Thread starter 9 months ago
#3
(Original post by Dylan8421)
Dative covalent bonding is when both electrons in the covalent bond come from the same atom.

As boron has 3 electrons in its outer shell it can form 3 covalent bonds with each chlorine where each atom donates 1 electron to the bond so each chlorine can gain a full outer shell.
I understand that each chlorine atom has a full shell through covalent bonding, but by boron forming 3 covalent bonds it would only have 6 electrons in its outer shell (3 from its original outer shell and 1 from each chlorine atom, so an extra 3).

But why doesn't one of the chlorine atoms share 2 of its own electrons via a dative covalent bond so that boron has a full outer shell (since 6+2=8)?
0
reply
scimus63
Badges: 9
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#4
Report 9 months ago
#4
BCl3 does not have an octet of electrons, it only has 6e in the valence shell, look here
https://www.science-revision.co.uk/A...ctet_rule.html
0
reply
5hyl33n
Badges: 21
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#5
Report 9 months ago
#5
(Original post by DoubleJazzy)
Recently I answered an exam style question which asked me to draw a dot and cross diagram for BCl3, showing outer electrons only.

The actual answer showed a boron atom in the centre, with 3 covalent bond electron pairs surrounding it from each chlorine atom.

Following the octet rule, I drew an extra two electrons from one of the chlorine atoms to signify a dative covalent bond, however this seems to be incorrect.

Why is it incorrect, and in what situation would I use dative covalent bonding?

James
Step 1
Write out the number of outer electrons of BCl3

Step 2
Boron has 3 electrons in its outer shell.
Cl has 7 electrons in its outer shell.

Step 3
Therefore, to get a full outer shell, each chlorine needs to gain one electron and the boron needs to lose all three electrons. Therefore, each chlorine will take one electron from the boron.


Spoiler:
Show
Name:  BCl3.png
Views: 284
Size:  14.8 KB
0
reply
charco
Badges: 18
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#6
Report 9 months ago
#6
(Original post by DoubleJazzy)
I understand that each chlorine atom has a full shell through covalent bonding, but by boron forming 3 covalent bonds it would only have 6 electrons in its outer shell (3 from its original outer shell and 1 from each chlorine atom, so an extra 3).

But why doesn't one of the chlorine atoms share 2 of its own electrons via a dative covalent bond so that boron has a full outer shell (since 6+2=8)?
Good question (and studiously ignored by the subsequent posters).

The electron deficient structure only occurs in the gaseous state, while the solid boron trichloride has tetrahedral boron atoms with full octets in a polymeric structure.

Why can it not form a dative coordinate bond with a chlorine lone pair?

The answer is because it is energetically unfavourable to do so ... but why is that the case?

I can only imagine that is has something to do with the electropositive nature of the boron atom (electronegativity 2.04) not being attractive enough for the electron pair compared to the electronegative chlorine atom (electronegativity 3.16) .

Boron also has no available 'd' orbitals to make the process easier. It does have an available 'p' orbital but, that is apparently not good enough in the gaseous state.
1
reply
DoubleJazzy
Badges: 4
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#7
Report Thread starter 9 months ago
#7
(Original post by charco)
Good question (and studiously ignored by the subsequent posters).

The electron deficient structure only occurs in the gaseous state, while the solid boron trichloride has tetrahedral boron atoms with full octets in a polymeric structure.

Why can it not form a dative coordinate bond with a chlorine lone pair?

The answer is because it is energetically unfavourable to do so ... but why is that the case?

I can only imagine that is has something to do with the electropositive nature of the boron atom (electronegativity 2.04) not being attractive enough for the electron pair compared to the electronegative chlorine atom (electronegativity 3.16) .

Boron also has no available 'd' orbitals to make the process easier. It does have an available 'p' orbital but, that is apparently not good enough in the gaseous state.
Ahhhh that makes so much more sense! I completely disregarded the electro negativity of the boron atom, thank you so much!
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest

How did The Student Room help you with your university application?

Talking to current university students (8)
24.24%
Talking to peers going through the same thing (10)
30.3%
Speaking to student ambassadors from the universities (2)
6.06%
Speaking to staff members from universities (0)
0%
Using the personal statement builder, library or helper service (3)
9.09%
Reading articles about what steps to take (6)
18.18%
Learning about/speaking to Student Finance England (2)
6.06%
Something else (tell us in the thread) (2)
6.06%

Watched Threads

View All