Question

Explain why it takes more energy to remove the second electron from a lithium atom than it does to remove the fourth electron from a carbon atom

Short answer

In summary, it takes more energy to remove the second electron from a lithium atom than it does to remove the fourth electron from a carbon atom because the second electron in lithium is closer to the nucleus with no electron shielding, while the fourth electron in carbon is slightly farther away from the nucleus and experiences shielding from the remaining 2s² electrons in the C³⁺ ion.

Step-by-step solution

Determine the electron configurations of Lithium and Carbon

First, consider the electron configurations of lithium and carbon. The electron configuration of lithium (Li) is 1s² 2s¹, while that of carbon (C) is 1s² 2s² 2p².

Identify the electrons being removed

We are asked to compare the energy required to remove the second electron from lithium and the fourth electron from carbon. This means we will remove the electron from 2s¹ in lithium to become the Li⁺ ion (with the electron configuration 1s²) and from 2p² in carbon to become the C³⁺ ion (with the electron configuration 1s² 2s²).

Recall the concept of ionization energy

Ionization energy is the energy required to remove one electron from an atom or ion. The ionization energy depends on several factors: the nuclear charge, the distance between the nucleus and the outermost electrons, and electron shielding.

Compare ionization energies

When removing the second electron from lithium (Li to Li⁺), we are removing an electron from the second energy level (2s¹), which is close to the nucleus, and the electron has no shielding from the attractive force of the nucleus. This makes it difficult to remove, and thus requires more energy. However, when removing the fourth electron from carbon (C to C³⁺), we are removing an electron from the second energy level (2p²). Although it is also close to the nucleus, it is slightly farther away than the 2s electron we removed from the lithium atom due to higher angular momentum. Additionally, the remaining 2s² electrons in the C³⁺ ion provide some shielding from the nucleus, making it easier to remove the fourth electron from a carbon atom compared to removing the second electron from a lithium atom.

Conclusion

To sum up, it takes more energy to remove the second electron from a lithium atom than it does to remove the fourth electron from a carbon atom because the second electron in lithium is closer to the nucleus with no electron shielding, while the fourth electron in carbon is slightly farther away from the nucleus and experiences shielding from the remaining 2s² electrons in the C³⁺ ion.

Key concepts

Electron Configuration

Electron configuration refers to the distribution of electrons in an atom's electron shells. It gives us insights into the atom's properties, including its ionization energy. For example, the electron configuration of lithium is

• 1s² 2s¹

This configuration shows that lithium has three electrons, with two filling the first energy level and one in the second.
Meanwhile, carbon, with its electron configuration

• 1s² 2s² 2p²

possesses six electrons, with two in the first level and four in the second. The electrons in the highest energy levels are usually the ones involved in reactions. Understanding their configuration helps us predict ionization energies for elements.

Nuclear Charge

Nuclear charge in an atom is the positive charge of the nucleus due to its protons. It significantly influences ionization energy, as a strong nuclear charge means a greater force holding the electrons close.

• For lithium, there are three protons, and in carbon, there are six.

The greater the number of protons, the higher the nuclear charge, increasing the hold on the electrons. Yet, even with a higher nuclear charge, other factors like electron distance and shielding affect ionization.

Electron Shielding

Electron shielding refers to the reduction in effective nuclear charge on the electron cloud, due to the presence of other electrons between the nucleus and the valence electrons. In simpler terms, it is the way inner electrons can "shield" outer electrons from the full effect of the nucleus's pull.

In lithium, the second electron is removed from the 2s orbital. This electron is very close to the nucleus, experiencing the full nuclear pull without inner electron protection.
On the other hand, in carbon, removing the fourth electron (from the 2p orbital) faces some shielding from the inner 2s electrons, making it slightly easier to remove. The concept of shielding helps in understanding why similar elements in different rows of the periodic table can differ in their chemical behavior.

Energy Levels

Energy levels, also known as electron shells, signify the probable distance of an electron from the nucleus. Electrons in the outermost levels are usually the easiest to remove, requiring less ionization energy.
When we look at lithium, its electrons are in the 1s and 2s energy levels, with the 2nd level being the outermost. Thus, the electron here is strongly held by the nucleus and requires more energy to remove.
In carbon, while its electrons also reside in the second-level orbitals, the presence of

• 2s
• 2p

orbitals allows for some distance and increased energy, which impacts the ease of removing electrons. The understanding of energy levels is key to predicting and explaining the ionization energy differences among atoms.