4.1.5 : Reaction mechanisms

Question 1

What is a covalent bond?

Answer 1

A covalent bond is a strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

Question 2

Describe what happens in homolytic fission?

Answer 2

Bond splits evenly - happens when a covalent bond breaks and each bonding atom receives one electron from the bonded pair, forming two radicals.

Question 3

What are radicals?

Answer 3

Radicals are species with one or more unpaired electrons - shown as dots

Question 4

What is the general equation for homolytic fission?

Answer 4

X–Y -> X. + Y.

Question 5

Describe what happens in the homolytic fission of Cl2

Answer 5

• In Cl2, there is a shared pair of electrons between the atoms
• When UV radiation is added, this causes the covalent bond to break
• One electron from the covalent bond goes to each chlorine atom forming two identical (highly energetic) radicals

Cl–Cl -> 2Cl.

Question 6

What are free radicals?

Answer 6

Free radicals are atoms/groups of atoms which have a single unpaired electron

Question 7

What is a reaction mechanism?

Answer 7

Reaction mechanisms are models that show the movement of electron pairs during a reaction

Question 8

What do curly arrows show?

Answer 8

Curly arrows model the flow of electrons

Question 9

How are covalent bonds formed?

Answer 9

When two radicals, or oppositely charged ions, collide.

Question 10

What makes carbocations very reactive?

Answer 10

They are unstable

Question 11

Describe what happens in heterolytic fission

Answer 11

Bond splits unevenly - happens when a covalent bond breaks and both electrons go to one of the bonded atoms, resulting in a positive ion (cation) and a negative ion (anion) being formed

Question 12

What is the general equation for heterolytic fission?

Answer 12

X–Y -> X+ + Y-