Alkenes

Name a reaction in which an alkane is a reactant and an alkene is a product

Cracking

Why are alkenes more reactive than alkanes?

The double bond in alkenes is electron rich and therefore, makes them more reactive

What type of reactions do alkenes undergo?

Electrophilic addition reactions

What are the reactants in an alkene addition reaction called?

Electrophiles.

What are stereoisomers?

Molecules with the same molecular and structural formula, but a different 3-D arrangement of the atoms (in space).

What are the two types of stereoisomers?

Geometric and optical

What kinds of isomers can alkenes have?

Structural and geometric isomers.

When do geometric isomers form?

When there is a C=C double bond present in a molecule. The carbon atoms cannot rotate around the double bond.

What makes a geometric isomer E?

The high priority atoms are on opposite sides

What makes a geometric isomer Z?

The high priority atoms are on the same side

What gives an atom/ group of atoms a higher priority?

A higher atomic number

In what other types of alkene molecules is there restricted rotation around C-C single bonds?

Cyclic molecules.

What are optical isomers?

They exist as molecules which are non-superimposable on their mirror image form.

What else are molecules which show optical isomerism called?

Chiral molecules

How can you tell if a molecule is chiral?

If one of the carbon atoms is single bonded to 4 different atoms or groups

What is a single bond between carbon atoms (and C-H) called?

A sigma bond

What does a double bond between two carbon atoms consist of?

A sigma bond and a pi bond

Position of pi bond in regards to sigma bonds

The electron clouds which make up the pi bond are above and below the plane of the molecule

How are molecular orbits formed?

When bonds are formed between atoms, atomic orbital overlap forming molecular orbits.

Sigma bonds

Formed by the overlap between two s orbitals, an s and p orbital or two p orbitals. In this bond, the shared pair of electrons lie on the axis between two nuclei.

Pi bonds

Formed by the sideways overlap between the overlap of two p orbitals. Electrons are free to move.

Why are pi bonds weaker than sigma bonds?

The electrons are slightly further from the nuclei of the carbon atoms. Therefore, they are more susceptible to attack by electrophiles.