Question

Refer to the periodic table and state the noble gas with an electron configuration identical to each of the following ions: (a) \(\mathrm{Se}^{2-}\) (b) \(\mathrm{Br}^{-}\) (c) \(\mathrm{Rb}^{+}\) (d) \(\mathrm{Sr}^{2+}\)

Short answer

All the given ions (a-d) have an electron configuration identical to Krypton (Kr).

Step-by-step solution

Understand the Problem

We need to identify the noble gas that each given ion's electron configuration matches. A noble gas configuration is represented by a fully filled energy level.

Identify Ground State Electron Configurations

Determine the atomic number and original electron configuration for the neutral atom of each element: - Selenium (Se) is atomic number 34. - Bromine (Br) is atomic number 35. - Rubidium (Rb) is atomic number 37. - Strontium (Sr) is atomic number 38.

Determine the Electron Configurations of Ions

Add or remove the appropriate number of electrons to each element to form the ion:(a) For \(\mathrm{Se}^{2-}\): Add 2 electrons.(b) For \(\mathrm{Br}^{-}\): Add 1 electron.(c) For \(\mathrm{Rb}^{+}\): Remove 1 electron.(d) For \(\mathrm{Sr}^{2+}\): Remove 2 electrons.

Match with Noble Gas

Find which noble gas matches the electron configuration obtained for each ion:(a) \(\mathrm{Se}^{2-}\) and (b) \(\mathrm{Br}^{-}\) both match the electron configuration of Krypton (Kr), which has 36 electrons.(c) \(\mathrm{Rb}^{+}\) and (d) \(\mathrm{Sr}^{2+}\) both match the electron configuration of Krypton (Kr) as well.

Key concepts

Periodic Table

The periodic table is like a map for chemists. It organizes all known elements in a structured way based on their atomic number, electron configurations, and recurring chemical properties. The table helps predict the types of chemical reactions that an element can participate in. Elements are sorted into rows called periods and columns named groups.

Moving left to right across a period, the atomic number increases, meaning each element has one more proton and, generally, one more electron than the element before it. This organization means elements with similar properties typically line up in the same column. For instance, noble gases are all found in the far-right column of the table.

Understanding where an element is on the periodic table can tell us a lot about its behavior and the energy levels its electrons occupy. This is crucial when considering electron configurations and how closely they align with those of noble gases.

Ions

An ion is formed when an atom gains or loses electrons. This process results in the atom having a net positive or negative charge. Atoms seek to have a stable electron configuration, often resembling that of a noble gas. This is because noble gases naturally have full outer electron shells, making them chemically inert and stable.

There are two main types of ions: cations and anions. Cations are positively charged because they have lost electrons, while anions are negatively charged due to gaining electrons. For example:

• Selenium (Se) gains 2 electrons to become \( ext{Se}^{2-}\), forming an anion.
• Bromine (Br) gains 1 electron to form \( ext{Br}^{-}\), another anion.
• Rubidium (Rb) loses 1 electron to become \( ext{Rb}^{+}\), a cation.
• Strontium (Sr) loses 2 electrons to form \( ext{Sr}^{2+}\), also a cation.

Ion formation is a key concept in understanding how elements interact with each other in chemical reactions.

Electron Configuration

Electron configuration describes how electrons are distributed within an atom’s orbitals. Each orbital can hold a set number of electrons: 2 in s orbitals, 6 in p orbitals, 10 in d orbitals, and 14 in f orbitals. Electron configuration helps predict chemical bonding behavior and reactivity.

An atom’s electrons occupy the lowest energy levels first—not unlike filling seats from the front row to the back in a theater. The aim is often to fill or half-fill outermost energy levels, as atoms with full or half-full orbitals tend to be more stable. This drive for stability often guides the formation of ions.

For example, when selenium ( ext{Se}) gains 2 electrons, it achieves the same electron configuration as krypton (Kr), a noble gas. This mimicking of noble gas electron configurations is a stabilizing move for elements transitioning into ions.

Noble Gases

The noble gases are a group of inert gaseous elements located in Group 18 of the periodic table. They are known for having fully filled outer electron shells, which makes them extremely stable and unreactive. This stability is a result of their electron configurations, where the outer shell is completely filled.

Examples of noble gases include:

• Helium (He) with a full 1s shell
• Neon (Ne) with a full 2s and 2p shell
• Argon (Ar) continuing the pattern with a full 3p shell
• Krypton (Kr), which matches with the ions \( ext{Se}^{2-}\) and \( ext{Br}^{-}\), as well as \( ext{Rb}^{+}\) and \( ext{Sr}^{2+}\)

Their inertness explains why elements often seek electron configurations similar to noble gases when forming ions. This drive for stability makes noble gas configurations a frequent goal in chemical reactions and elemental transformations.