Why have we used n=1 in the question The species which has fifth ionization potential equal to 340 volts is(A) B+(B)C+(C)B(D)C

To understand why we use \( n=1 \) in the context of the question regarding the species with a fifth ionization potential of 340 volts, we need to delve into the concept of ionization energy and how it relates to the electronic configuration of elements.

Ionization Energy Explained

Ionization energy is the energy required to remove an electron from an atom or ion in its gaseous state. The first ionization energy refers to the energy needed to remove the first electron, the second ionization energy for the second electron, and so on. When we talk about the fifth ionization potential, we are discussing the energy required to remove the fifth electron from an atom or ion.

Understanding the Notation

In the question, the notation \( n=1 \) typically refers to the principal quantum number of the electron shell from which the electron is being removed. For many elements, the electrons are removed from different shells as you continue to ionize the atom. The first few electrons are usually removed from the outermost shell, which corresponds to higher values of \( n \). However, as you remove more electrons, you may start removing them from inner shells, which have lower values of \( n \).

Application to the Given Species

Now, let’s analyze the options provided: B⁺, C⁺, B, and C. The question implies that we are looking for a species that has a fifth ionization potential of 340 volts. To determine which species this could be, we need to consider their electronic configurations and how many electrons they have.

• Boron (B) has an atomic number of 5, with the configuration 1s² 2s² 2p¹. It can lose up to 3 electrons easily, but removing a fifth electron would require significant energy, likely from an inner shell.
• C (Carbon) has an atomic number of 6, with the configuration 1s² 2s² 2p². Similar to boron, it can lose 4 electrons, but the fifth would also be from a more stable inner shell.
• B⁺ and C⁺ are ions of boron and carbon, respectively. The ionization potentials would change due to the loss of one electron, but the trend remains similar.

Why n=1?

When we reach the fifth ionization, we are likely removing an electron from a more stable inner shell, which corresponds to \( n=1 \) for many elements. This is because after removing the outer electrons, the remaining electrons are more tightly bound to the nucleus, requiring significantly more energy to remove them. Thus, for elements like boron and carbon, the fifth ionization energy reflects the energy needed to remove an electron from the 1s orbital, which is why we refer to \( n=1 \).

Final Thoughts

In summary, the use of \( n=1 \) in this context helps us understand the energy dynamics involved in removing electrons from different shells of an atom. The fifth ionization potential being 340 volts indicates that we are dealing with a situation where the electron being removed is from a very stable inner shell, which is characteristic of elements with low atomic numbers like boron and carbon. This understanding is crucial for predicting the behavior of elements in chemical reactions and their ionization energies.