Question

Describe how the ionization energies of the ions ${\mathrm{He}}^{-},{\mathrm{Li}}^{-},{\mathrm{Be}}^{-},{\mathrm{B}}^{-},{\mathrm{C}}^{-},{\mathrm{N}}^{-},{\mathrm{O}}^{-},$ and ${\mathrm{F}}^{-}$ vary with atomic number.

Short answer

The ionization energies of the ions He-, Li-, Be-, B-, C-, N-, O-, and F- increase with increasing atomic number. This is because the increased number of protons in the nucleus of larger atoms more strongly attracts the electrons, thus requiring more energy to remove one.

Step-by-step solution

Understand Ionization Energy

Ionization energy is the energy required to remove an electron from an atom or ion in its gaseous state. It is also important to remember that Ionization energy generally increases moving from left to right across a period (the horizontal rows in the periodic table of elements).

Consider Atomic Structures

The atomic number determines the number of protons in an atom, and generally, the number of electrons in a neutral atom. All the ions mentioned are negatively charged, meaning they have one extra electron than their neutral state. Therefore, they all have a similar electronic configuration.

Rule of Thumb

As a rule of thumb, ionization energy increases with atomic number because the increasing number of protons attracts the electrons stronger, making it harder to remove one. The ions He-, Li-, Be-, B-, C-, N-, O-, and F- will thus show an ascending trend in ionization energy as their atomic number increase. Exceptions to this rule can occur due to the stability of certain electron configurations.

Key concepts

Periodic Table Trends

When examining periodic table trends, ionization energy is a key aspect to understand. It tends to increase as you move from left to right across a period. This trend happens because atoms have more protons as you go across a period. This increased positive charge in the nucleus pulls electrons closer, making it tougher to remove one.
However, exceptions can occur due to the specific arrangement of electrons, known as electron configuration. For negatively charged ions like ${\mathrm{He}}^{-},{\mathrm{Li}}^{-},{\mathrm{Be}}^{-},$ and others, the general trend is that ionization energy increases with the atomic number. The more protons in the nucleus, the stronger the pull on the extra electron.

• Ionization energy increases left to right across periods.
• More protons result in stronger attraction of electrons.
• Some exceptions could be due to stable electron arrangements.

Atomic Structure

The atomic structure consists of protons, neutrons, and electrons. Every element has a distinct number of protons, known as its atomic number. This number also tells us how many electrons are in a neutral atom.
In ions, the number of electrons differs from the neutral state. For negatively charged ions like ${\mathrm{He}}^{-},{\mathrm{Li}}^{-},{\mathrm{Be}}^{-},$ etc., there is one extra electron. This affects their ionization energy. The added electron occupies the outer shell, slightly altering interactions within the atom.
More protons mean a larger positive charge pulling on these electrons. As the atomic number increases, this pull becomes stronger, making it more difficult to ionize the atom.

• Atomic number = number of protons/electrons in neutral atoms.
• Extra electrons in ions affect their energy properties.
• Increased atomic number leads to stronger electron attraction.

Electron Configuration

Electron configuration describes how electrons are distributed around an atom's nucleus. Electrons fill orbitals in a specific order, with each shell and subshell accommodating a defined number.
For negatively charged ions like ${\mathrm{He}}^{-},{\mathrm{Li}}^{-},{\mathrm{Be}}^{-},$ and others, the electron configuration is key to understanding their ionization energy. The extra electron fills the next available orbital, often leading to new, possibly unstable configurations.
These configurations influence not just ionization energy but also chemical behavior and reactivity. The more stable the electron configuration, the harder it might be to ionize the atom, which can cause exceptions in periodic trends.

• Electron configuration determines electron distribution.
• Extra electrons in ions fill available orbitals.
• Configuration stability affects ionization energy and reactivity.