Question

Compare the first ionization energy of helium to its second ionization energy, remembering that both electrons come from the \(1 s\) orbital. Explain the difference without using actual numbers from the text.

Short answer

The second ionization energy of helium is significantly higher than its first ionization energy due to the stronger attraction between the remaining electron in the \(1s\) orbital and the nucleus. When the first electron is removed, the electron shielding effect is reduced, and the remaining electron experiences a greater nuclear charge, making it harder to remove. Thus, the second ionization energy requires more energy for the second electron removal compared to the first electron removal.

Step-by-step solution

Review the concept of ionization energy

Ionization energy is the required energy to remove an electron from an atom or ion. The greater the ionization energy, the more difficult it is to remove an electron from an atom. There are two types of ionization energy: first ionization energy and second ionization energy. The first ionization energy corresponds to the energy required to remove one electron from an atom, while the second ionization energy is the energy required to remove a second electron from the ion.

Consider electron shielding in the 1s orbital

In the 1s orbital, there are two electrons. When the first electron is removed, the remaining electron will experience less electron shielding. This means that the remaining electron will have a stronger interaction with the nucleus, and will be more difficult to remove.

Examine the effect of nuclear charge on ionization energies

Helium has a nuclear charge of +2, which means that there are two protons in its nucleus. When the first electron is removed, the remaining electron experiences a stronger nuclear charge. As a result, the second ionization energy will be higher than the first ionization energy, because the remaining electron will be more strongly attracted to the nucleus and harder to remove.

Discuss the difference in ionization energies without using numbers

The second ionization energy of helium is significantly higher than its first ionization energy because the remaining electron in the 1s orbital experiences a greater nuclear charge and less shielding from other electrons. This stronger attraction to the nucleus leads to a higher energy requirement for the second electron removal compared to the first electron removal.

Key concepts

First Ionization Energy

The first ionization energy is a fundamental concept in chemistry. It refers to the energy needed to remove the outermost electron from a neutral atom. In simple terms, imagine you are trying to pluck an apple from a tree. The first ionization energy represents the effort you need to make to take that first apple. Helium, for example, has two electrons in its 1s orbital. The first ionization energy for helium involves removing one electron from this orbital. At this stage, you only need to overcome the attraction between that electron and the positive nucleus. Because it's the first electron being removed, there's no need to worry about changes to the electron environment yet. The first ionization energy is crucial because it gives insight into how tightly an atom holds onto its electrons and influences chemical reactivity.

Second Ionization Energy

The second ionization energy is another important aspect to consider. After the first electron is removed, the atom becomes a positively charged ion. Removing a second electron requires a different amount of energy because the conditions inside the atom have changed.
The second ionization energy is usually higher than the first. This is because once an electron is removed, the remaining electrons are pulled closer to the nucleus due to the reduced electron-electron repulsion.
With helium, after the first electron is gone, the second one is held more tightly by the nucleus. It faces a stronger overall pull from the nucleus, as there is now one less electron to counterbalance the nuclear charge. This increased nuclear attraction means that significantly more energy is needed to remove a second electron.
When examining any element, observing the jump between first and second ionization energies can provide valuable clues about the element's electron configuration and its tendency to form ions.

Electron Shielding

Electron shielding is a subtle concept but plays a critical role in understanding ionization energies. It describes how inner electrons can block outer electrons from feeling the full force of the nucleus. Think of it like a blanket insulating outer electrons from the nucleus’s charge.
In helium, both electrons are in the 1s orbital. Before any ionization occurs, they shield each other's nuclear attraction minimally because they are so close to the nucleus.
When the first electron is removed, there is no longer any electron in the way of the nucleus for the remaining electron. This lack of shielding leads to a stronger attraction between the remaining electron and the nucleus, contributing to why the second ionization energy is higher.

Nuclear Charge

Nuclear charge is simply the total charge of all the protons in the nucleus. It's a key factor in determining how strongly electrons are held by an atom.
In the case of helium, with a nuclear charge of +2, it means the nucleus contains two protons. These protons exert a positive pull on the electrons.
When considering ionization energies, the effective nuclear charge – the net positive charge experienced by an electron – plays a big part.
After the first electron is removed from helium, the remaining electron feels the entire +2 charge almost unshielded. This amplified experience of nuclear charge increases the force needed to remove the next electron. It's this strength of nuclear charge that makes the second ionization energy of helium much greater than the first. Understanding these charges helps explain why elements behave the way they do in different chemical reactions.