MYTUTOR SUBJECT ANSWERS

560 views

What is benzene and describe the 2 models used to explain it's structure. Provide a piece of evidence to show which of these models is incorrect.

Benzene

With a formula of C6H6, the molecule has a cyclic structure due to it's 6 carbon atoms joined in a ring. It is symmetrically planar (flat) with it's 6 hydrogen's sticking out in the same plane. There are two models used to explain benzene's structure- the Kekulé model and the delocalised model.

The Kekulé model

Proposed by the German chemist Friedrich August Kekulé in 1865, he hypothesised that carbon could exist in a ring with alternating single and double bonds between them.

(At this point, a digram would be drawn of a standard skeletal benzene structure and the molecular structure diagram showing all the carbons and hydrogens, see 'Benzene structure according to Kekule' in text books for illustration)

If this model were correct, there would be 3 bond lengths of a C-C bond (147pm) and 3 bonds with the length of a C=C bond (135pm). However, X-ray diffraction have shown that all the carbon-carbon bonds within benzene are of the same length of 140pm, suggesting that the model is incorrect. This value shows that the carbon bonds have a length between that of a single bond and a double bond.

The delocalised model

This phenomenon can be explained by the delocalised model. In this model, the p-orbitals (check AS notes) of all 6 carbon atoms overlap to create π bonds. Two ring-shaped clouds of electrons form with one above and one below the plane of the 6 carbon atoms.

(At this point, you'd draw a diagram of the formation of π bonds in benzene due to the overlap of p-orbitals)

With this, carbon-carbon bonds are the same length (140pm) as the bonds are all identical. The electrons in the rings are said to be delocalised because they don't belong to a specific carbon atom. They are then represented as a circle in the ring of carbons instead of double and single bonds in a diagram.

(You would then illustrate this as a skeletal or molecular diagram)

Alexander M. A Level Chemistry tutor, GCSE Chemistry tutor, A Level B...

8 months ago

Answered by Alexander, an A Level Chemistry tutor with MyTutor


Still stuck? Get one-to-one help from a personally interviewed subject specialist

70 SUBJECT SPECIALISTS

£20 /hr

Thomas D.

Degree: Neuroscience (Bachelors) - Kings, London University

Subjects offered: Chemistry, Science+ 3 more

Chemistry
Science
Physics
Maths
Biology

“I am currently in my second year of a Neuroscience Bachellors' degree at a Russel Group institution, that is King's College London. Having done five (yes 5) A2s, and achieved an A* and 5 As, I know a few tricks of the trade so to spea...”

£22 /hr

Daniel W.

Degree: Chemistry and Maths (Bachelors) - Leeds University

Subjects offered: Chemistry, Maths

Chemistry
Maths

“Me, Myself & I I am studying Chemistry and Maths at the University of Leeds and I am about to go into the second year of my degree. From quite an early age I realised Maths and Science are where my interests lie.  I volunteered as a ...”

£20 /hr

Catherine H.

Degree: Biochemistry with Psychology (Bachelors) - Exeter University

Subjects offered: Chemistry, Science+ 1 more

Chemistry
Science
Biology

“I am a third year student at the University of Exeter studying for a BSc in Biochemistry with Psychology. I find science really exciting and would love to show you why! These tutoring sessions will be tailor-made to you. Whatever yo...”

About the author

£20 /hr

Alexander M.

Degree: BSc Biochemistry with a year in Industrial Placement (Bachelors) - Exeter University

Subjects offered: Chemistry, Maths+ 2 more

Chemistry
Maths
Biology
-Personal Statements-

“Who am I? Me My name is Alexander McDermott and I am currently undergoing a BSc Biochemistry with industrial experience degree from the University of Exeter. My fascination and passionfor science has been growing throughout my academic...”

MyTutor guarantee

You may also like...

Other A Level Chemistry questions

What are covalent bonds?

What are the different types of bonding in chemicals?

The recommended daily allowance of methionine for an adult is 15 mg per kg of body mass. Tuna contains 755 mg of methionine per 100 g portion. Calculate the mass, in grams, of tuna that would provide the RDA of methionine for a 60 kg adult.

What is an isotope?

View A Level Chemistry tutors

Cookies:

We use cookies to improve our service. By continuing to use this website, we'll assume that you're OK with this. Dismiss

mtw:mercury1:status:ok