11.5 Introduction to reaction mechanisms

Question 1

What is a covalent bond

Answer 1

Defined as a shared pair of electrons between two atoms.

Question 2

How can covalent bonds be broken

Answer 2

By either homolytic fission or heterolytic fission

Question 3

What happens when a covalent bond is broken by homolytic fission

Answer 3

Each of the bonded atoms takes ONE of the shared pair of electrons from the bond

• Each atom now has a single unpaired electron
• An atom or groups of atoms with an unpaired electron is called a radical

Question 4

Homolytic fission of the carbon-carbon bond in ethane (equation)

Answer 4

H3C-CH3 -> H3C•+•CH3

Question 5

What happens when a covalent bond is broken by heterolytic fission

Answer 5

One of the bonded atoms takes BOTH of the electrons from the bond

• The atom that takes both electrons becomes a negative ion
• The atom that does not take the electrons becomes a positive ion

Question 6

Heterolytic fission of the carbon-chlorine bond in chloromethane, CH3Cl (Equation)

Answer 6

H3C-Cl -> H3C+ + Cl-

Question 7

What is the process of the reaction mechanism

Answer 7

How the reaction takes place

Question 8

What is used to show the movement of electron pairs when bonds are being broken or made, in a reaction mechanism

Answer 8

Curly arrows

Question 9

What does a fish-hook arrow represent

Answer 9

The movement of a single, unpaired electron in mechanisms involving radicals

Question 10

What happens in an addition reaction

Answer 10

Two reactants join together to form one product

Question 11

What happens in a substitution reaction

Answer 11

An atom or group of atoms is replaced by a different atom or group of atoms

Question 12

What happens in an elimination reaction

Answer 12

Involves the removal of a small molecule from a larger one

One reactant molecule forms two products.