Chapter 4- Chemical bonding Flashcards Preview

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Flashcards in Chapter 4- Chemical bonding Deck (41)
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Resonance structures

When 2 or more lewis structures can be drawn OR when there is more than one possible position for a multiple pi bond


Resonance hybrid

Is the form of the molecule that is the more stable than either one of it's resonance structure and it's said to have delocalised bonds.


Examples of molecules that have resonance structures (3)

+ Benzene
+ Carbonate ion
+ Ozone


Formal charge

The charge that an atom would carry if ALL the bonding electrons were split equally between the 2 atoms joined by the bond.
→ FC = (No. of valence e-) - (1/2 No. of bonding e- + No. of lonepair e-)


The sum of the formal charge = ?

The charge on the ion


The lower the number of atoms with formal charges?

The more stable the structure
→ why resonance structures that have the least number of atoms carrying a FC is preferred


How to figure out formal charge?

The nuclear charge (charge on the nucleus) - the number of electrons in the the atom (bonding, non-bonding and in inner orbital)


Bond order

The average number of bonds of the different resonance structures


What happens to the charge carried by the atoms in a resonance structure?

It is also averaged



Valence Shell Electron Pair Repulsion


4 electron domains that are all bonded has the shape and bond angle of? + example

+ Tetrahedral
+ 109.5
E.g = Methane


3 electron domains are bonded and 1 lone pair has the shape and bond angle of? + example

+ Triangular Pyramidal
+ 107
E.g = Ammonia NH3


2 bonding electron domains and 2 non-bonding pairs has the shape and bond angle of? + example

+ Bent/ Non-linear
+ 104
E.g = Water


When there are 2 electron domains with NO non-bonding pair what is the shape and the bond angle? + example (not serious)

+ Linear
+ 180
E.g = Beryllium Chloride, CO2


3 electron domains bonded and NO non-bonding pair of electrons?

+ Trigonal Planar
+ 120
E.g = Boron Fluoride, Methanal


3 electron domains bonded and 1 non-bonding pair of electrons?

+ Non-linear (V-shaped)
+ 117
E.g = Sulfur dioxide


Bonding in Diamond (GIANT covalent structure)

+ C atom joined by 4 other
+ Tetrahedral arrangement
+ sp3 hybridisation
+ 109.5


Bonding in Silicon dioxide (GIANT covalent structure)

+ Si bonded to 4 other Oxygens


Bonding in Graphite (GIANT covalent structure)

+ 2 covalent network in 2 dimensions
+ only has dispersion forces betw/ the 2 sheets of C atoms = weak forces = can easily slide over e.o = lubricant
+ C bonded to 3 others forming a hexagon
+ 120 bond angle + sp2 hybridization
+ all atoms contribute one electron to the delocalised pi-bond
+ Delocalised electrons allow it to conduct electricity in 2D


C60/ Buckminsterfullerene/ Fullerene (GIANT covalent structure)

+ Spherical mol.
+ made of 5 and 6 membered C ring
+ C bonded by sigma-bond to 3 other carbons
+ sp2 hybridization
+ LITTLE delocalization of unpaired electrons = cuz surface of sphere = not planar → electrons can't easily flow from one C60 to the next


How is the electrical conductivity of Fullerene?

Better than diamond but worse than graphite


What species does C60 behave as?

+ electron deficient mol. that readily accepts electrons from reducing agents to form anions with a variety of charges


What type of reactions do fullerene undergoe?

Addition reactions


Unlike diamond = fullerenes are molecular so what properties do they have that differ from graphite and diamond?

+ Dissolve in non-polar solvent
+ low m.p



2D material = single sheet of graphite structure


Delocalised bonds

When sideways interactions of p-orbitals to form a pi-bond can involve more than 2 atoms → p-orbitals can extend over more than 2 nuclei so electrons are hared by a number of atoms


Why does delocalization make the molecule more stable?

It gives the species a lower potential energy than it would if it was composed of normal double and single bonds


How is Stratospheric Ozone formed?

+ Photodissociation of O2 molecules caused by UV light from sun to produce O ATOMS.


Mechanism for Photodissociation of O2

O2 (g) → (UV light) 2O• (g)
Oxygen atoms are v. reactive and combine with O2 mol. to form Ozone:
O2 (g) + O• (g) → O3 (g)


UV light also causes photodissociation of Ozone itself. State the mechanism.

O3 (g) → (UV light) O2 + O• (g)
O3 (g) + O• → 2O2 (g)
This results in an equilibrium concentration of Ozone in the Stratosphere