Covalent Bonds Flashcards
Pi bond
P orbitals overlap sideways/collaterally which results in a concentration of the electron density above and below the internucleus axis.
Sigma bond
Orbitals overlap head-on/collinearly which results in a concentration of the electron density between the nuclei of bonding atoms.
Why is sigma bond stronger than pi bond?
Sigma hind has more extensive overlap of orbitals.
Diamond - allotrope
Each carbon atom is joined to 4 other carbon atoms by strong covalent bonds to form a tetrahedral structure.
Uses: jewelry, in saws and drills to cut solids
Graphite - allotrope
Each carbon atom in the layer is bonded to 3 other carbon atoms via strong covalent bonds to form a hexagonal arrangement of carbon atoms.
The 4th valence electron of each carbon atom is delocalised between the layers of carbon atoms.
Layers are held together by weak van der Waals’ forces.
Uses: pencil lead, lubricant
Silicon - allotrope
Each silicon atom is joined to 4 other silicon atoms by strong covalent bonds to form a tetrahedral structure.
Uses: semi-conductor used in the manufacture of chips in micro-electronics
Silicon dioxide - allotrope
Each silicon atom is joined to 4 oxygen atoms and each oxygen atom is joined to 2 silicon atoms by strong covalent bonds to form a tetrahedral structure.
Uses: making of glass
G(a) High melting and boiling points
A large amount of energy is required to overcome the strong covalent bonds between atoms.
G(b) Hard
A large amount of energy is required to overcome the strong covalent bonds between atoms.
Exception: Graphite.
Strong covalent bonds exist between the carbon atoms in the layers but weak van der Waal’s’ forces hold the layers together. Only a small amount of energy is required to overcome the weak forces, allowing the layers to slide over each other. (Used as a lubricant)
G(c) Non-conductor or electricity
No mobile charge carriers present as all valence electrons are involved in the formation of covalent bonds.
Exception: Graphite
Presence of delocalised electrons along the layers allow graphite to conduct electricity in a direction parallel to the layers by migration of electrons when a potential difference is applied.
G(d) Insoluble in all solvents (polar/non-polar)
Energy released during the formation of solute-solvent interaction is insufficient to overcome the strong covalent bonds.
S(a) Low melting and boiling points
Small amount of energy required to overcome the weak intermolecular forces holding the discrete molecules together.
S(b) Non-conductors of electricity
As they exist as discrete uncharged molecules, there is an absence of mobile charge carriers.
S(c) Soft
Small amount of energy is required to overcome the weak intermolecular forces holding the discrete molecules together.
S(d) Soluble in solvents of similar polarity
“Like dissolves like”
Non-polar:
Iodine + organic solvents like hexane and methylbenzene
Polar:
Ethanol + water as solvent
