Question

Which noble gas is isoelectronic with each of the following nonmetal ions? (a) \(\mathrm{Br}^{-}\) (b) \(\mathrm{O}^{2-}\) (c) \(\mathrm{Se}^{2-}\) (d) \(\mathrm{N}^{3-}\)

Short answer

(a) $Kr$, (b) $Ne$, (c) $Kr$, (d) $Ne$.

Step-by-step solution

Understanding the Concept of Isoelectronic

Isoelectronic species are atoms or ions that have the same number of electrons. To find a noble gas that is isoelectronic with a given ion, we must determine the total number of electrons in the ion.

Determine Electrons in  $Br^{-}$$

A neutral bromine ($Br$) atom has 35 electrons. The bromide ion ($Br^{-}$) has gained one extra electron, resulting in a total of 36 electrons.

Find Isoelectronic Noble Gas for $Br^{-}$$

The noble gas with 36 electrons is krypton ($Kr$). Hence, $Br^{-}$ is isoelectronic with $Kr$.

Determine Electrons in $O^{2-}$$

A neutral oxygen ($O$) atom has 8 electrons. The oxide ion ($O^{2-}$) has gained two extra electrons, resulting in a total of 10 electrons.

Find Isoelectronic Noble Gas for $O^{2-}$

The noble gas with 10 electrons is neon ($Ne$). Therefore, $O^{2-}$ is isoelectronic with $Ne$.

Determine Electrons in $Se^{2-}$

A neutral selenium ($Se$) atom has 34 electrons. The selenide ion ($Se^{2-}$) gains two extra electrons, leading to a total of 36 electrons.

Find Isoelectronic Noble Gas for $Se^{2-}$

The noble gas with 36 electrons is krypton ($Kr$). Thus, $Se^{2-}$ is isoelectronic with $Kr$.

Determine Electrons in $N^{3-}$

A neutral nitrogen ($N$) atom has 7 electrons. The nitride ion ($N^{3-}$) has gained three extra electrons, leading to a total of 10 electrons.

Find Isoelectronic Noble Gas for $N^{3-}$

The noble gas with 10 electrons is neon ($Ne$). Therefore, $N^{3-}$ is isoelectronic with $Ne$.

Key concepts

Noble Gases

Noble gases are a group of elements found in the far-right column of the periodic table. They include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). What makes noble gases special is their stability. They have a full set of electrons in their outer shell, making them unlikely to react with other elements. This stability is what other elements often strive for. When atoms or ions are said to be isoelectronic with a noble gas, it means they have achieved the same electron configuration and stability. Elements and ions often aim to mimic the electron structure of noble gases to gain similar stability. When an atom gains or loses electrons to form an ion, it tries to match the electron configuration of the nearest noble gas. In many chemical reactions, elements will react and form bonds so that they can "borrow" or "share" electrons to reach a noble gas configuration.

Electron Configuration

Electron configuration describes the arrangement of electrons around an atom's nucleus. Electrons are organized in shells and subshells, following the principles of quantum mechanics. The specific order follows a pattern of increasing energy levels. Each electron shell consists of subshells labeled as s, p, d, and f. These subshells hold a specific number of electrons: s can hold 2, p can hold 6, d can hold 10, and f can hold 14. For example, the element neon has an electron configuration of 1s² 2s² 2p⁶. This means it has 10 electrons distributed across its shells. Understanding electron configurations is crucial in identifying isoelectronic species. By determining the total number of electrons in an ion and comparing it to noble gases, you can find which noble gas it mirrors. Elements adjust their number of electrons through gain or loss to achieve the stable electron configuration of the noble gases.

Ions

Ions are atoms or molecules that have gained or lost electrons, resulting in a net charge. If an atom loses an electron, it becomes a positively charged cation. Conversely, if it gains an electron, it becomes a negatively charged anion.The formation of ions is often a result of the atom's pursuit of stability, which can be achieved by reaching an electron configuration similar to that of the noble gases. Let's look at some examples:

• The bromide ion (\( \mathrm{Br}^{-} \)) has 36 electrons, making it isoelectronic with krypton (\( \mathrm{Kr} \)).
• The oxide ion (\( \mathrm{O}^{2-} \)) with 10 electrons is isoelectronic with neon (\( \mathrm{Ne} \)).
• Selenide ion (\( \mathrm{Se}^{2-} \)) also has 36 electrons like krypton (\( \mathrm{Kr} \)).
• The nitride ion (\( \mathrm{N}^{3-} \)) matches neuron's configuration with 10 electrons.

Understanding ions is vital to many aspects of chemistry, from predicting element behavior to balancing chemical equations. It's all about achieving that coveted noble gas electron configuration for many elements.