Question

You will need to consider ionizations beyond the first ionization energy. For example, the second ionization energy is the energy to remove a second electron from an element. Compare the first ionization energy of helium to its second ionization energy, remembering that both electrons come from the 1 s orbital.

Short answer

The first ionization energy (IE1) of helium is the energy required to remove one electron, forming a positive ion (He -> He⁺ + e⁻). The second ionization energy (IE2) is the energy required to remove a second electron from the positively charged ion (He⁺ -> He²⁺ + e⁻). After removing the first electron, the remaining electron experiences a stronger electrostatic attraction to the nucleus, resulting in a significantly higher second ionization energy. The first ionization energy of helium is approximately \(2372.3\, kJ/mol\), while its second ionization energy is \(5250.5\, kJ/mol\).

Step-by-step solution

1. Understand the atomic structure of Helium

The helium atom has a total of 2 electrons, both are present in the 1s orbital. The electronic configuration of helium is 1s².

2. Define the first and second ionization energies

The first ionization energy (IE1) is the energy required to remove one electron from an atom, forming a positive ion (He -> He⁺ + e⁻). The second ionization energy (IE2) is the energy required to remove a second electron from the positively charged ion (He⁺ -> He²⁺ + e⁻).

3. Analyze factors that affect ionization energy

Several factors affect ionization energy, including: - Atomic radius: smaller atoms have higher ionization energies because electrons are closer to the nucleus and more strongly attracted. - Shielding effect: the larger the number of inner electron shells, the more shielding. This reduces the effective nuclear charge experienced by the outer electrons, resulting in lower ionization energy. - Nuclear charge: higher nuclear charges (more protons) result in more powerful attraction of electrons and higher ionization energies. In the case of helium, with only two protons, its nuclear charge is relatively low compared to other elements.

4. Compare the first ionization energy of helium to its second ionization energy

For helium, removing the first electron doesn't involve breaking a strong electrostatic attraction, as there's only one other electron in the orbital. However, when removing the second electron, the remaining electron is now attracted more strongly to the nucleus (due to the increased positive charge of He⁺). Thus, the second ionization energy (IE2) will be significantly higher than the first ionization energy (IE1). In numbers, the first ionization energy of helium is approximately \(2372.3\, kJ/mol\), while its second ionization energy is \(5250.5\, kJ/mol\), clearly showing that the second ionization energy is noticeably higher than the first ionization energy. This is mainly because the remaining electron experiences a stronger electrostatic attraction to the nucleus after the first electron has been removed.

Key concepts

Atomic Structure

Understanding atomic structure is vital when studying chemistry, particularly when delving into topics like ionization energy. The atomic structure refers to the composition and arrangement of protons, neutrons, and electrons within an atom. Protons and neutrons form the nucleus at the center, while electrons orbit around this nucleus in specific energy levels or shells.

In the simplest atom, hydrogen, there is a single electron orbiting a single proton. Helium, the second element, has two protons in its nucleus and two electrons in the first shell, known as the 1s orbital. These electrons are held in place by the electric force exerted by the positively charged nucleus. Since helium has only one shell, and that shell can hold a maximum of two electrons, it's a complete orbital, making helium a noble gas with a stable electronic arrangement.

Knowing the atomic structure of helium is essential for understanding why its ionization energies behave the way they do. The compact structure with a small, positively charged nucleus tightly holding two electrons provides the basis for why it requires certain amounts of energy to remove those electrons—energies that we measure as the first and second ionization energies.

First Ionization Energy

The first ionization energy (often abbreviated as IE1) is a fundamental concept in chemistry that describes the energy required to remove the first electron from an isolated neutral atom in its gaseous state to form a cation. It's a quantitative measure of how tightly an atom holds onto its electrons.

For instance, the first ionization energy of helium is high, given its small radius and the strong attraction between the two electrons and the nucleus. In helium's case, since the two electrons are in the same orbital, they partially shield each other from the full attraction of the nucleus. However, helium is a notable exception to the trend where ionization energy generally increases across a period; it has a higher IE1 despite having a filled shell, a testament to the strength of its nucleus's hold on its electrons.

The value for helium's first ionization energy is roughly 2372.3 kJ/mol. This high value is due to its electrons being close to the nucleus, thus feeling a strong electrostatic attraction. In general, the first ionization energy provides insight into an element's reactivity and its tendency to form compounds.

Second Ionization Energy

The second ionization energy (IE2) moves us a step further in ionization energies, representing the energy necessary to remove the second electron from an atom that has already lost one electron (thus from a monopositive ion). The second ionization energy is always higher than the first because it is even harder to remove an electron from a positively charged ion than from a neutral atom.

In the context of helium, which has a first ionization energy of 2372.3 kJ/mol, the second ionization energy is an astounding 5250.5 kJ/mol. This dramatic increase is because once the first electron is removed, the second electron is more strongly attracted to the now more positively charged nucleus. Remember, an electron has been removed, so the ratio of protons to electrons has changed; there are now more protons per electron than before, resulting in a stronger electrostatic force pulling the remaining electron towards the nucleus.

This heightened second ionization energy illustrates why an element like helium does not typically lose a second electron and why the noble gases are generally nonreactive. Ionization energies, especially when analyzing successive ones, reveal a lot about the electron affinity and chemical disposition of an element.