xplain why the value of the band gap energy, Eg, decreases in the following homologous series:
Cdiamond=5.4 eV; Si=1.1 eV; Ge=0.72eV; Sn=0.08 eV.
As we move down the group, bond strength increases. As the strength increases, materials become more metallic in nature, since metals are strong. Metals tend to conduct electrons more easily, hence the band gap must decrease as materials become more metallic in nature.
Bond strength increases as we move down a group in the periodic table. The increasing bond strength tightens the spread between the valence and conduction bands, which in turn lowers the band gap of the material and allows it to be more conductive.
Due to the increasing nuclear mass, the bond strength decreases as we go down the group in the periodic table, and the resulting bonds within the material are weaker, meaning they require less energy to remove electrons, leading to a smaller band gap.
Due to the increasing atomic radius, valence electrons are more weakly bound, therefore the bond strength decreases as we go down the group in the periodic table, and the resulting bonds within the material are weaker, meaning they require less energy to remove electrons, leading to a smaller band gap.
What is your question for us?
Explain from the 4 reasons given:
a
b
c or
d ?
thanx
ANKUR answer is D
To determine why the value of the band gap energy decreases in the given homologous series, we need to analyze the factors that affect the band gap energy.
The band gap energy is the energy difference between the valence band (the highest-energy band occupied by electrons) and the conduction band (the lowest-energy band that can accept electrons and allow them to move freely). A larger band gap means that it requires more energy for electrons to transition from the valence band to the conduction band, making the material less conductive.
Now, let's consider the different factors that influence the band gap energy in this homologous series:
1. Atomic mass: As we move down the group from carbon (C) to tin (Sn), the atomic mass increases. This increase in atomic mass leads to an increase in the strength of the bonds between atoms. Stronger bonds require more energy to break, resulting in a larger band gap energy. Therefore, the atomic mass alone does not explain the decreasing trend in the band gap energy.
2. Atomic radius: As we move down the group, the atomic radius increases. With larger atomic radius, the valence electrons are more weakly bound to their respective atoms. Weaker bonds between atoms require less energy to break, resulting in a smaller band gap energy. Thus, the increasing atomic radius contributes to the decreasing trend in the band gap energy.
3. Metallic nature: As we move down the group, the metallic nature of the elements increases. Metals have more delocalized electrons, allowing for easier electron movement and conductivity. To transition from the valence band to the conduction band, electrons in metals require less energy. This leads to a smaller band gap energy for more metallic elements, such as tin (Sn), compared to less metallic elements, such as carbon (C).
In summary, the decreasing trend in the band gap energy in this homologous series can be explained by the combined effects of increasing atomic radius and increasing metallic nature as we move down the group in the periodic table.