Alkenes and their Bonding

Question 1

what is the difference between alkenes and alkanes

Answer 1

• alkanes only have single bonds between their carbon atoms

- whereas alkenes have at least one double bond between a pair of carbon atoms

Question 2

what does it make alkenes if they have at least one C=C bond

Answer 2

unsaturated

Question 3

between alkanes and alkenes which one is more common

Answer 3

alkanes

Question 4

how do you get alkenes

Answer 4

• they dont naturally occur in nature

- so they have to be made through cracking alkanes

Question 5

what would the structural formula for ethene be

Answer 5

CH2=CH2

Question 6

what would the structural formula for propene be

Answer 6

CH2=CH-CH3

Question 7

what would the structural formula of cis-but-2-ene be (just explain)

Answer 7

• there would be a C=C bond in the middle
• with a CH3 coming from the left and right carbon atom
• both at opposite sides from each other (Z-isomer)
• two Hs would be bonded to a C each as well

Question 8

what is the general formula of an alkene

Answer 8

CnH2n

Question 9

what is a common cyclic alkene and what is its structural formula

Answer 9

• cyclohexene
• CH=C(H)-C(H2)-C(H2)-C(H2)-C(H2)-back to the first CH
• the hydrogens are in brackets as to show that it is the carbon atoms that are bonded together to make the ring

Question 10

what is an advantage that alkenes have over alkanes due to their C=C bond

Answer 10

• they are more reactive than alkanes

- so they can be used in many more useful reactions

Question 11

why does using the C=C symbol seem to be misleading about how the carbon atoms are bonded

Answer 11

• because it implies that the two bonds between the carbon atoms are the same
• when they are not

Question 12

how many atoms are the carbon atoms in a C=C bond bonded to

Answer 12

• 2 other atoms
• as two bonds are being used to bond with another carbon atoms
• where it would normally have 4
• as carbon has 4 electrons in its outer shell

Question 13

what does covelant bonding between atoms usually involve

Answer 13

• the overlapping of the orbitals of two different atoms

- these could be 2 s orbitals, 2 p orbitals or one of each

Question 14

what are all these bonds represented by when drawn and what is the example when drawing hydrogen gas

Answer 14

• a line

- so hydrogen gas, H2, would be drawn as H-H

Question 15

what can all of these simpler covelant bonds be called

Answer 15

• sigma bonds

- also known as o (with a line on top) bonds

Question 16

when sigma bonds are formed between carbon atoms in an alkene, what is their formation called

Answer 16

• formation by axial overlap

- or end-on overlap

Question 17

in a molecule of ethene, how many sigma bonds would each carbon atoms have

Answer 17

• 3

- because they are bonded with one carbon atom and 2 hydrogens each

Question 18

what does that mean regarding the electrons in carbons outer shell

Answer 18

• the two carbon atoms each have one electron in a p orbital left
• which hasnt been used in bond formation

Question 19

what is the relationship between the p orbitals in this molecule of ethene and what does it mean

Answer 19

• they are parallel to each other
• and so are not able to overlap with each other
• in the same way as in the formation of sigma bonds

Question 20

however, what happens when the p orbitals do overlap

Answer 20

it results in the formation of two regions of negative charge above the C-C sigma bond

Question 21

how would this bond between p orbitals form in the first place

Answer 21

it is formed by the sideways overlap of orbitals

Question 22

what are these types of bonds called

Answer 22

• pi bonds

- also known as (literally the sign for pi) bonds

Question 23

if each of these regions of negative charge contain one electron, what is made

Answer 23

• they make up a second pair of electrons
• between the carbon atoms
• as one region of negative charge is above the C-C sigma bond and the other is under

Question 24

what is different about the electrons in the pi bond compared to the sigma bond

Answer 24

they are further away from the carbon atoms than the electrons in the sigma bonds are

Question 25

what does it mean if the electrons in the pi bond are further away from the carbon atoms

Answer 25

• they can be though of as less under control by the carbon atoms
• and therefore more available for reactions
• this is why they are more reactive than alkanes