Chemical Bond Flashcards

1
Q

What is electronegativity? (2)

A

• The ability of an atom in a molecule to attract electrons to itself.
• On the periodic table, electronegativity increases as you go…
– …from left to right across a row.
– …from the bottom to the top of a column.

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2
Q

The most stable (most likely) structure has: (2)

A
  • the lowest formal charge on each atom

* the most negative formal charge on the most electronegative atom.

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3
Q

There are three classes of exceptions to the octet rule:

A
  1. molecules with an odd number of electrons,
  2. molecules in which one atom has less than an octet, and
  3. molecules in which one atom has more than an octet.
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4
Q
  • In predicting molecular shape, a molecule adopts the 3D-dimensional geometry that minimizes the ______ between the valence electrons.
  • The arrangement that minimizes repulsions depends on the number of electron _____.
A

repulsion

domains

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5
Q

How is the shape of a molecule determined?

A

• The shape of a molecule is determined by its bond angles i.e. the angles made by the lines joining the nuclei of the atoms in a molecule.

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6
Q

How is the shape and size of a molecule determined?

A

• The bond angles and bond lengths accurately define the shape and size of a molecule.

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7
Q

Name the electron domain geometry & bond angles of a structure with 2 electron domains:

A
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8
Q

Name the electron domain geometry & bond angles of a structure with 3 electron domains:

A
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9
Q

Name the electron domain geometry & bond angles of a structure with 4 electron domains:

A
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10
Q

Name the electron domain geometry & bond angles of a structure with 5 electron domains:

A
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11
Q

Name the electron domain geometry & bond angles of a structure with 6 electron domains:

A
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12
Q

Name the molecular of a structure with 2 electron domains:

A
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13
Q

Name the molecular of a structure with 3 electron domains:

A
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14
Q

Name the molecular of a structure with 4 electron domains:

A
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15
Q

Name the molecular of a structure with 5 electron domains:

A
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16
Q

What is the effect of electron domains on bond angles?

A

Electron domains for non-bonding electron pairs exert greater repulsive forces on adjacent electron domains and thus tend to compress the bond angles.

17
Q

Name the molecular of a structure with 6 electron domains?

A
18
Q

What are the levels of hybridisation? (6)

A
19
Q

Pi (π) Bond:

A

Pi (π) Bond: this results from the overlap between two p orbitals orientated perpendicularly to the internuclear axis.

20
Q

Why are pi bonds weaker than sigma bonds?

A

Because of the sideways overlap of the p orbitals, total overlap in a pi-bond tends to be less than in a sigma-bond; pi-bonds are weaker than sigma-bonds.

21
Q

What is bond enthalpy?

A

The strength of a bond is measured by determining how much energy is required to break the bond.

22
Q
  • A double bond consists of one __ -bond and one __-bond.

* A triple bond consists of one ___-bond and two ___-bonds.

A

sigma; pi

sigma; pi

23
Q
  • The unhybridized p orbitals on carbon are involved in ___-bonding.
  • ___-bonds require that portions of a molecule be planar therefore they can introduce rigidity into molecules.
A

pi

pi

24
Q

Which atoms can form pi bonds?

A
  • bonds can form only if unhybridized p orbitals are present on the bonded atoms
  • only atoms having sp or sp2 hybridization can be involved in pi bonding
25
Q

• Characteristics of Molecular orbitals:

> Like atomic orbitals. (3)

A

 Each contains a maximum of two electrons with opposite spins.
 Each has a definite energy.
 Electron density distribution can be visualized with contour diagrams.

26
Q

> Bonding MO: Lower-energy MO – why? (2)

A

> Concentrates electron density between the nuclei, so the bonding MO holds the atoms together in a covalent bond.
Results from the AO wave functions enhancing each other in the bonding region.

27
Q

Antibonding MO: Higher energy MO – why? (2)

A

> The greatest electron density is on opposite sides of the nuclei. This MO excludes electrons from the region in which a bond must form.
Results from the AO wave functions cancelling each other in the bonding region.

28
Q

The stability of a covalent bond is related to its bond order:

A

Bond order = ½ (bonding electrons – antibonding electrons)

29
Q
– Bond order = _ for a single bond. 
– Bond order = _ for a double bond. 
– Bond order = _ for a triple bond. 
– Fractional bond orders are possible  some molecules 
have an odd no. of electrons. 
–  Bond order = _ ----> NO BOND FORMS
A

1
2
3
0

30
Q

• As bond order increases:

A

• As bond order increases: bond length decreases and bond energy increases.

31
Q

Two types of magnetic behaviour are: (i) Paramagnetism (3)

A

– Unpaired electrons in the molecule
– Strong attraction between magnetic field and molecule
– The more unpaired electrons, the stronger the attraction

32
Q

Two types of magnetic behaviour are: (ii) Diamagnetism (2)

A

– no unpaired electrons in molecule

– weak repulsion between magnetic field and molecule

33
Q

True or false

Diamagnetism is a much weaker effect than Paramagnetism

A

True

34
Q

How do you know if bond is delocalized?

A

The lone pairs next π bonds are delocalized because they are in the p orbital of an sp2 hybridized atom. If the lone pairs can participate in forming resonance contributors – they are delocalized, if the lone pairs cannot participate in resonance, they are localized.