C3 Electrons and orbitals

Question 1

what is meant by principal quantum number?

Answer 1

• principal quantum number (n) refers to rows of the periodic table
• first shell, n=1
• second shell, n=2 etc.

Question 2

what is secondary quantum number (l)?

Answer 2

• each shell has a number of subshells which is defined as the secondary quantum number

Question 3

what can the secondary quantum number (l) range from and to?

Answer 3

• ranges from 0 to n-1
• s, l=0
• p, l=1
• d, l=2
• f, l=3

Question 4

what does the l value of a subshell determine?

Answer 4

the shape of the sub shell’s orbitals
- s subshell, l=0 which means spherical orbitals
- p subshell, l=1 which means dumbbell orbitals
etc.

Question 5

what is magnetic quantum number?

Answer 5

• ranges from -l to l and describes how many orientations the orbitals of each subshell can take up
• eg. for p orbitals, l=1 so magnetic quantum number ranges from -1 to 1.
• this means the values can be -1, 0 or 1 so there are 3 orientations that the p orbitals can take up

Question 6

what is spin quantum number?

Answer 6

• spin quantum number relates to angular momentum of an electron
• electrons can be spin up (+1/2) or spin down (-1/2)

Question 7

what does the Aufbau principle state?

Answer 7

• orbitals fill in order from lowest energy level to highest

Question 8

what does the Pauli exclusion principle state?

Answer 8

• every electron in each orbital must have a unique spin
• no 2 electrons in 1 atom can have the exact same set of 4 quantum numbers (principle, secondary, magnetic, spin)

Question 9

what does Hund’s rule state?

Answer 9

• in a half filled subshell, it is favourable in terms on energy for electrons to have parallel spins (each orbital has 1 electron before any of them gain a second)

Question 10

what is the order of repulsion of different pairs of electrons?

Answer 10

bonded-bonded <
lone-bonded <
lone-lone

Question 11

where does atomic orbital (AO) theory break down?

Answer 11

• electronic model says carbon should only make 2 bonds (2 p orbitals have 1 space)
• VSEPR theory says carbon should make bonds at 90 degrees because 3p orbitals are at 90 degrees

Question 12

what is orbital hybridisation theory? eg. consider carbon atom in methane

Answer 12

• 2s orbital and 3 x 2p orbitals are mixed to form sp3 hybridised orbitals
• the 4 x sp3 hybridised orbitals of carbon overlap with the 1s orbitals in each of the hydrogen atoms
• both share one electron to form 4 sigma bonds
• the 4 sp3 orbitals repel as far as possible to give the 109.5 degree angles

Question 13

what is orbital hybridisation theory? eg. consider carbon atom in ethene

Answer 13

• 2s orbital and 2 x 2p orbitals are mixed to form 3 x sp2 orbitals
• there is also a 2p orbital that isn’t hybridised which is then able to form the pi bond between the 2 carbon molecules
• hybridised sp2 orbitals are orientated at 120 degrees in a trigonal planar shape

Question 14

what is the difference between the orbital overlap in sigma and pi bonding? give examples in terms of the overlap in ethene

Answer 14

• sigma bonds arise from end-on orbital overlap
  eg. hybridised sp2 orbitals in an ethene molecule
• pi bonds arise from side-on overlap
  eg. unhybridised orbitals in an ethene molecule

Question 15

what happens with orbital hybridisation in a carbon atom in an ethyne molecule?

Answer 15

• a 2s orbital and a 2p orbital mix to form 2 x sp orbitals
• the 2 x sp orbitals are linear with the 2 remaining unhybridised p orbitals at 90 degrees

Question 16

how are sp3, sp2 and sp hybridised orbitals related to single, double and triple carbon bonding?

Answer 16

• sp3 relates to single bonded carbons
• sp2 relates to double bonded carbons
• sp relates to triple bonded carbons