Magwen
Badges: 2
Rep:
?
#1
Report Thread starter 6 years ago
#1
The question says,

Chemists are able to predict the shape of a simple covalent molecule from the number of electron pairs surrounding the central atom.

Explain how this enables chemists to predict the shape.
0
reply
Anonymous 14
Badges: 1
Rep:
?
#2
Report 6 years ago
#2
(Original post by Magwen)
The question says,

Chemists are able to predict the shape of a simple covalent molecule from the number of electron pairs surrounding the central atom.

Explain how this enables chemists to predict the shape.
Opposite charges attract so two negative electrons will repel.

say you have beryllium chloride the electrons from each atom will repel one another forming a linear shape.
0
reply
Basmaa
Badges: 0
Rep:
?
#3
Report 6 years ago
#3
The electron pairs will aim to repel in a way that results in the maximum distance between them.

CO2... The oxygens are on opposite sides therefore forming a linear molecule, with a 180 degree repulsion, because that's the greatest distance they can achieve between them.

However, H2O forms a bent molecule because of the lone pairs of electrons on the oxygen atom, which exert a greater repulsion force. So the distance between the two hydrogens would be less (I think 140.5, I don't remember...)

You'll need to know common shapes (tetrahedral, trigonal planar etc.) and the estimated degree of repulsion between molecules.


Posted from TSR Mobile
0
reply
hasan6091
Badges: 16
Rep:
?
#4
Report 6 years ago
#4
Posted from TSR Mobile

unbonded pairs repell more than bonded pairs ....
0
reply
Protoxylic
Badges: 14
Rep:
?
#5
Report 6 years ago
#5
Bonding pairs of electrons repel equally around the central atom. For example, BCl3 - boron trichloride. The central atom is Boron, its valence is 3 (meaning 3 valence electrons), it can covalently bond to 3 chlorine atoms. Because a covalent bond is created via a shared pair of electrons, one from Boron, one from chlorine, this creates a 'bonding pair' of electrons. These pairs of electrons repel each other via electrostatic repulsion, and they do so to gain the furthest distance between each other - or more simply, repel equally. If you know that Boron has a valence of three, and has 3 chlorines bonded to it, you know that the bond angle is going to be 360/3 = 120 degrees. Lone pairs of electrons repel more than bonding pairs, meaning that central atoms that contain lone pairs of electrons - take ammonia NH3, Nitrogen has a valence of 3 with a lone pair to create dative covalent bonds. NH3 has a tetrahedral shape, but with a lone pair, making the bond angle reduce from a normal 109.5 for tetrahedrons, to a 107.5 degrees triangular pyramid shape. Lone pairs reduce the bond angle of a shape by roughly 2 degrees per lone pair.

This is long winded, and most of it will not be used to answer your question, but it gives you theory to understand it more rather than a stencil to answer a question. If you need more information, consult the VSEPR theory section of a Chemistry textbook.
0
reply
X

Quick Reply

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

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

What do you want most from university virtual open days and online events?

I want to be able to watch in my own time rather than turn up live (181)
28.64%
I want to hear more about the specifics of the course (105)
16.61%
I want to be able to dip in and dip out of lots of different sessions (58)
9.18%
I want to meet current students (53)
8.39%
I want to meet academics and the people that will be teaching me (51)
8.07%
I want to have a taster lecture or workshop to see what the teaching is like (126)
19.94%
My parents/guardians are more interested than me to be honest (38)
6.01%
Other things – I'll tell you in the thread (20)
3.16%

Watched Threads

View All