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MED 102- GENERAL CHEMISTRY > 12. MOLECULAR ORBITAL THEORY > Flashcards

12. MOLECULAR ORBITAL THEORY Flashcards

1
Q
  1. What does molecular Orbital Theory focus on?
A
  • it focuses on the chemical bonds formed by placing electrons in molecular orbitals
  • it looks at the electron arrangement in molecules
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2
Q
  1. What do Molecular Orbitals cover?
A
  • they cover the entire molecules
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3
Q
  1. What do Molecular orbitals allow for?
A
  • excited electronic states
  • types of bonds (single, double, triple) to be determined
  • allow for magnetic properties of the molecules to be determined
    (does it go towards or away from the magnetic field)
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4
Q
  1. What happens when 2 1s atomic orbitals are joined together mathematically?
A
  • they form two molecular orbitals
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5
Q
  1. What type will these two Molecular Orbitals be?
    Where will they be located?
A
  • they will be of sigma (σ) type
  • one will be at lower energy
  • one will be at higher energy
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6
Q
  1. Which molecular orbital is at higher energy?
    How is this indicated?
A
  • the anti-bonding orbital will be at higher energy
  • it is indicated by an asterisk
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7
Q
  1. Which molecular orbital will be at lower energy?
A
  • the bonding orbital
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8
Q
  1. Where is the electron density concentrated between two bonding molecular orbitals?

What does this promote?

A
  • it is between the two nuclei
  • it forms an ellipsoid electron cloud
  • this promotes bond formation
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9
Q
  1. What happens with the electron density in anti-bonding Molecular Orbitals?

What does this promote?

A
  • it is pushed away from the centre
  • this promotes bond destruction
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10
Q
  1. Where do we place the two Hydrogen electrons in a hydrogen molecule?
A
  • we place 2 electrons starting with the lowest bonding energy
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11
Q
  1. What exists between the two electron densities in the anti-bonding molecular orbital that pushes them away from the middle?
A
  • a node
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12
Q
  1. Why does helium prefer to stay not bonded (Monatomic)?
A
  • the average energy of the electrons is higher when the helium is diatomic
  • this makes it more unstable
  • there is no energetic benefit to helium being bonded
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13
Q
  1. How can Bond Order be Calculated?
A
  • Bond Order= 1/2 (NB- NAB)
  • NB= the number of bonding electrons
  • NAB= the number of anti bonding electrons
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14
Q
  1. What do the following values of Bonding orders mean:

14.1: BO= 0
14.2 BO= 1
14.3: BO= 2
14.4: BO= 3
14.5: BO= 1/2

A

14.1: there is no bond formed
: this means that there is no molecule
: the element exists as individual atoms

14.2: there is a single bond formed
14.3: there is a double bond formed
14.4: there is a triple bond formed
14.5: it is a half integer

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15
Q
  1. How would you put the electrons of the Hydrogen molecule into an excited electron state?
A
  • in Hydrogen’s ground electron state:
    - it has a bond order of 1
  • to put the Hydrogen electrons into an excited state:
    - you would promote an electron to the anti-bonding
    molecular orbital
    - you separate the two bonded electrons by doing this
    - the bond order now becomes zero
    - the molecule splits up
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16
Q
  1. What would happen if we were to promote a hydrogen electron to the σ₂s Molecular Orbital?
A
  • we would get a different excited state
  • ti would have a Bond Order of 1
  • this means that the molecule would still exist
17
Q
  1. What is the Bond Order for the H2+ Molecular Ion?
A
  • Number of electrons:
    2-1 = 1
  • there is only one electron in the H2+
  • it is placed in the σ1s molecular orbital
  • this is a bonding orbital
  • Bond Order: 1/2 (1-0)
    : this is equal to a half
18
Q
  1. What does a “half-bond” mean?
A
  • the covalent bond has approximately half the strength of a single covalent bond
  • ions produce half integer bonds
19
Q
  1. What happens when we combine two 2s atomic orbitals?
A
  • we get two molecular orbitals:
    - a σ2s Bonding orbital
    - a σ2s﹡Anti-Bonding Orbital
20
Q
  1. How would we bond two lithium atoms?
A
  • lithium has 3 electrons
  • two lithium atoms have 6 electrons
  • we start by:
    • placing the electrons in the molecular orbitals from
      lower to higher energy
    • we put 2 electrons in the σ1s bonding orbital
    • we put two electrons in the σ1s﹡ anti-bonding orbital
    • the last two go in the σ2s bonding orbital
  • Bond Order= 1/2 (4-2)
    = 1
    = one single bond
21
Q
  1. What happens when we combine 2p atomic orbitals?
A
  • when the 2p (dumbbell shaped) atomic orbitals come together head on:
    - they form sigma type Molecular Orbitals
    - σ2s and σ2s﹡
22
Q
  1. What happens when we combine 2p atomic orbitals that are parallel to each other?
A
  • they form pi-type Molecular Orbitals
  • two π2p bonding molecular orbitals will be formed
  • two π2p﹡anti-bonding molecular orbitals will be
    formed
23
Q
  1. How many molecular orbitals would we have if six 2p atomic orbitals were combined?
A
  • we would have six
24
Q
  1. Do Molecular Orbital Configurations for Diatomic Molecules show valence shell (n=1) electrons?
A
  • no
  • they also do not show the σ1s and the σ1s﹡ molecular orbitals
25
Q
  1. Does the Hund’s rule apply to Molecular orbitals?
A
  • it does
  • when two electrons are to be placed in orbitals of equal energy
  • they need to be placed spin up
  • and in separate orbitals
  • this is the case for B2 and O2
26
Q
  1. What is the Molecular Orbitals diagram for the
    O2 2+ molecular ion?
A
27
Q
  1. What is the bond order for the O2 2+ ion?
A

Bond Order= 1/2 (NB - NAB)
= 1/2 (8-2)
= 3

  • there is a triple covalent bond present
28
Q
  1. What produces stronger bonds in Molecular Orbitals?
A
  • removing electrons from the anti-bonding orbitals
  • adding electrons to the bonding orbitals
29
Q
  1. Define Paramagnetic.
A
  • being attracted to a magnetic field
30
Q
  1. Define Diamagnetic.
A
  • being weakly repelled by a magnetic field
31
Q
  1. What is a Paramagnetic molecule?
A
  • it is a molecule with one or more unpaired electrons
32
Q
  1. What is a Diamagnetic molecule?
A
  • it is a molecule where all the electrons are paired up
33
Q
  1. Read through this summary.
    Does everything make sense?
A
  • yes

MED 102- GENERAL CHEMISTRY (27 decks)

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