Chemical Bond Flashcards
What is electronegativity? (2)
• 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.
The most stable (most likely) structure has: (2)
- the lowest formal charge on each atom
* the most negative formal charge on the most electronegative atom.
There are three classes of exceptions to the octet rule:
- molecules with an odd number of electrons,
- molecules in which one atom has less than an octet, and
- molecules in which one atom has more than an octet.
- 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 _____.
repulsion
domains
How is the shape of a molecule determined?
• 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.
How is the shape and size of a molecule determined?
• The bond angles and bond lengths accurately define the shape and size of a molecule.
Name the electron domain geometry & bond angles of a structure with 2 electron domains:
Name the electron domain geometry & bond angles of a structure with 3 electron domains:
Name the electron domain geometry & bond angles of a structure with 4 electron domains:
Name the electron domain geometry & bond angles of a structure with 5 electron domains:
Name the electron domain geometry & bond angles of a structure with 6 electron domains:
Name the molecular of a structure with 2 electron domains:
Name the molecular of a structure with 3 electron domains:
Name the molecular of a structure with 4 electron domains:
Name the molecular of a structure with 5 electron domains:
What is the effect of electron domains on bond angles?
Electron domains for non-bonding electron pairs exert greater repulsive forces on adjacent electron domains and thus tend to compress the bond angles.
Name the molecular of a structure with 6 electron domains?
What are the levels of hybridisation? (6)
Pi (π) Bond:
Pi (π) Bond: this results from the overlap between two p orbitals orientated perpendicularly to the internuclear axis.
Why are pi bonds weaker than sigma bonds?
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.
What is bond enthalpy?
The strength of a bond is measured by determining how much energy is required to break the bond.
- A double bond consists of one __ -bond and one __-bond.
* A triple bond consists of one ___-bond and two ___-bonds.
sigma; pi
sigma; pi
- 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.
pi
pi
Which atoms can form pi bonds?
- 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
• Characteristics of Molecular orbitals:
> Like atomic orbitals. (3)
Each contains a maximum of two electrons with opposite spins.
Each has a definite energy.
Electron density distribution can be visualized with contour diagrams.
> Bonding MO: Lower-energy MO – why? (2)
> 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.
Antibonding MO: Higher energy MO – why? (2)
> 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.
The stability of a covalent bond is related to its bond order:
Bond order = ½ (bonding electrons – antibonding electrons)
– 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
1
2
3
0
• As bond order increases:
• As bond order increases: bond length decreases and bond energy increases.
Two types of magnetic behaviour are: (i) Paramagnetism (3)
– Unpaired electrons in the molecule
– Strong attraction between magnetic field and molecule
– The more unpaired electrons, the stronger the attraction
Two types of magnetic behaviour are: (ii) Diamagnetism (2)
– no unpaired electrons in molecule
– weak repulsion between magnetic field and molecule
True or false
Diamagnetism is a much weaker effect than Paramagnetism
True
How do you know if bond is delocalized?
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.
