Part A
Hybridisation
According to the valence bond theory, hybridization is mixing atomic orbitals to produce new hybridized orbitals better suited for pairing electrons to form chemical bonds because they have different energies and shapes than the original atomic orbitals. To link to four different atoms, for instance, the valence-shell s orbital combines with three other valence-shell atomic orbitals to produce four equivalent sp3 mixes placed in a tetrahedral arrangement around the carbon atom. Hybrid orbitals are symmetrically distributed in space and can be used to explain atomic bonding and molecular geometry (Fryhle and Snyder, 2022). Hybrid orbitals are typically created by mixing atomic orbitals with similar energies.
Explain The Sigma And pi Bonding And Link That To The Hybridisation
The Sigma (σ) Bond
This covalent bond is created when atomic orbitals in the internuclear axis cross directly and positively (same phase). Sigma bonds are the strongest covalent connections because the participating orbitals overlap. The electrons a bond contains are referred to as “electrons.” All single bonds generally contain sigma bonds. They can be made using the following atomic orbital combinations.
s-s Overlapping
In this overlapping, one’s orbital from each participating atom collides directly along the internuclear axis. One’s orbital must be partly full before it can overlap another’s. The example below demonstrates how two s orbitals can cross each other and create a sigma bond. In H2 molecules, where each H2 atom occupies a semi-s orbital, this overlap occurs.
s-p Overlapping
One half-filled p orbital and one half-filled s orbital overlap and form a covalent bond along the antinuclear axis of this kind.
This kind of overlap is observed in ammonia. An NH3 molecule comprises three sigma bonds, formed when the nitrogen atom’s 2px, 2py, and 2pz orbitals overlap with the hydrogen atom’s 1s orbitals.
p-p overlapping
One half-filled p orbital from each participating atom encounters head-on overlap along the internuclear axis. To make Cl2, two chlorine atoms’ 3pz subshells must overlap in a p-p configuration. While the production of pi bonds is caused by the lateral overlap of these orbitals, establishing a sigma bond is caused by the head-to-head overlapping of two p orbitals.
Pi (π) Bond
Atomic orbitals that cross over sideways and are positive perpendicular to the internuclear axis form pi bonds. Atomic orbital axes are transverse to the internuclear axis whenever they overlap, but they are parallel when bonds are formed.
Sigma bonds are frequently weaker than pi bonds since there is significantly less overlapping. A double bond normally consists of one pi bond and one sigma bond, while a triple bond typically consists of two and one. It is imperative to keep in mind that a pair of sigma and pi bonds will always be more potent than an individual sigma bond (Iverson et al., 2022).
Part B
Explain why alkenes are much more reactive than alkanes towards chlorine (CL2) or bromine (BR2) in the dark at room temperature and why alkanes do not react with HCL (g) or HBr (g) whereas alkenes do.
The fundamental distinction between alkenes and alkanes, even though both are hydrocarbons, is that alkanes are saturated with just single covalent bonds (-bonds) between the carbon atoms, whereas alkenes are unsaturated molecules with a pair of covalent bonds (a combination of a -bond and a -bond). Due to the reactivity of the carbon-carbon bond, alkanes are generally stable compounds but are not more reactive than alkenes (Brown, 2022). The bulk of alkene reactions involves extending this bond with new single bonds. Halogen atoms can take the place of hydrogen atoms in an alkane. The process is referred to as a radical substitution mechanism because it includes the production of free radicals (Iverson et al., 2022).
References
Fryhle, C.B. and Snyder, S.A., 2022. Organic chemistry. John Wiley & Sons. Brown, W.H.,
Iverson, B.L., Anslyn, E. and Foote, C.S., 2022. Organic chemistry. Cengage Learning.
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