Question

Greater stability of hydrocarbons when compared to silanes is due to (1) high electronegativity of silicon than hydrogen (2) high electronegativity of hydrogen than carbon (3) high electronegativity of carbon than hydrogen (4) equal electronegativity of carbon and hydrogen

Short answer

The correct answer is (3) high electronegativity of carbon than hydrogen.

Step-by-step solution

Identify Key Concept

The stability of hydrocarbons compared to silanes is influenced by the electronegativities of the atoms involved. We need to compare the electronegativities of carbon, silicon, and hydrogen.

Electronegativity Comparison

Carbon has an electronegativity of 2.55, while hydrogen has an electronegativity of 2.20. Silicon has a lower electronegativity of 1.90 compared to both carbon and hydrogen.

Analyze Stability

The greater stability of hydrocarbons compared to silanes is because the bond between carbon and hydrogen is more stable due to the higher electronegativity of carbon compared to hydrogen. This creates a more stable covalent bond.

Choose Answer

Given the stability is due to the higher electronegativity of carbon compared to hydrogen, the correct option is (3) high electronegativity of carbon than hydrogen.

Key concepts

Electronegativity

Electronegativity is an essential concept in chemistry. It refers to the ability of an atom to attract electrons towards itself in a chemical bond. Differences in electronegativity between atoms can explain various chemical behaviors, including bond stability and molecule formation. In the context of hydrocarbons and silanes, comparing the electronegativities of carbon, hydrogen, and silicon helps us understand why certain bonds are more stable than others.
For instance, carbon has an electronegativity of 2.55, which is higher than hydrogen's 2.20. This difference explains why the carbon-hydrogen bond is quite stable. Meanwhile, silicon, with an electronegativity of just 1.90, cannot attract electrons as effectively as carbon.
This difference in ability to attract electrons contributes to the overall stability of molecules having carbon-hydrogen bonds compared to silicon-hydrogen bonds.

Carbon-Hydrogen Bond

The carbon-hydrogen bond is fundamental in organic chemistry. Its stability is one reason hydrocarbons (compounds of carbon and hydrogen) are highly stable.
Since carbon has a higher electronegativity (2.55) than hydrogen (2.20), the electrons are more attracted to the carbon atom in a C-H bond. This attraction makes the bond more stable and less reactive. A stable bond means that the molecule is less likely to break apart or react with other substances.
In comparison, silicon forms bonds with hydrogen that are less stable. This is partly because silicon's lower electronegativity (1.90) makes it less effective at holding onto the shared electrons in Si-H bonds. Consequently, hydrocarbons are generally more stable than silanes.

Silanes Stability

Silanes are compounds made up of silicon and hydrogen. Compared to hydrocarbons, these compounds are less stable, and the explanation lies in the electronegativity of silicon.
Silicon's electronegativity is 1.90, which is significantly lower than that of carbon (2.55). Because of this difference, the Si-H bond is weaker than the C-H bond. This weaker bond means silanes are more reactive and less stable than hydrocarbons.
Additionally, silicon is larger than carbon, which causes its bonds to hydrogen to be longer and weaker.
In summary, the electric pull that carbon exerts on its bonded hydrogen atoms makes hydrocarbons more stable—while the weaker pull in silanes leads to their lower stability.