Question

Write the complete and abbreviated electron configuration for each of the following ions. For each ion, identify another ion that is isoelectronic with it. (a) \(\mathrm{Na}^{+}\) (b) \(\mathrm{P}^{3-}\) (c) \(\mathrm{H}^{-}\)

Short answer

a) Na+: Electron Configuration is \(1s^2 2s^2 2p^6\). Isoelectronic ion is Mg2+. b) P3-: Electron Configuration is \(1s^2 2s^2 2p^6 3s^2 3p^6\). Isoelectronic ion is Ca2+. c) H-: Electron Configuration is \(1s^2\). Isoelectronic ion is He.

Step-by-step solution

Na+ Electron Configuration

To write the electron configuration for Na+, subtract one electron from the Na atom. Na has 11 electrons, but since it has lost one electron, Na+ has 10 electrons. The complete electron configuration for Na is \(1s^2 2s^2 2p^6 3s^1\). Thus, for Na+, remove the 3s^1, leaving you with \(1s^2 2s^2 2p^6\), which is the electron configuration of Ne, a noble gas.

Identify Isoelectronic Ion for Na+

An isoelectronic ion to Na+ would be Mg2+. Mg (magnesium) has 12 electrons, but when it loses 2 electrons to become Mg2+, it has the same number of electrons (10) as Na+ and Ne.

P 3- Electron Configuration

P (phosphorus) has 15 electrons, but with a 3- charge, it gains 3 more electrons, giving P3- a total of 18 electrons. The complete electron configuration for P3- is \(1s^2 2s^2 2p^6 3s^2 3p^6\), which is the configuration of Ar, a noble gas.

Identify Isoelectronic Ion for P3-

An isoelectronic ion to P3- would be Ca2+. Ca (calcium) has 20 electrons, but when it loses 2 electrons to become Ca2+, it has the same number of electrons (18) as P3- and Ar.

H- Electron Configuration

Hydrogen has 1 electron, but with a 1- charge, it gains 1 more electron, giving H- a total of 2 electrons. The electron configuration for H- is \(1s^2\), which is the configuration of He, a noble gas.

Identify Isoelectronic Ion for H-

An isoelectronic ion to H- would be He. Helium has 2 electrons, the same number as H-.

Key concepts

Isoelectronic Ions

When ions have the same number of electrons, they are referred to as isoelectronic ions. These ions share identical electron configurations but differ in the number of protons, which affects their chemical properties. Understanding isoelectronic ions helps in figuring out the similarities between different elements.
For instance, the ion \(\text{Na}^+\) is isoelectronic with \(\text{Ne}\), both having 10 electrons. Similarly, \(\text{P}^{3-}\) and \(\text{Ar}\) both have 18 electrons, making them isoelectronic. Lastly, \(\text{H}^-\) and \(\text{He}\) share two electrons. These examples show how ions from different elements can appear similar when it comes to electron count.

• Key Idea: Isoelectronic ions have the same electron count but differ in atomic numbers.

Identifying isoelectronic ions is useful because it links various ions to elements with stable configurations, often resembling that of noble gases.

Noble Gases

Noble gases are elements located in group 18 of the periodic table and are known for their full valence electron shells, making them chemically inert or non-reactive. Their stable electron configurations are often target configurations for other ions.
When ions gain or lose electrons, they often aim to achieve a configuration similar to that of a noble gas. This is because noble gases have a complete octet, except for helium, which has a full 1s shell.

• For example: \(\text{Na}^+\) modifies its electron configuration to match \(\text{Ne}\)'s, which is a noble gas.
• \(\text{P}^{3-}\) rearranges its electrons to share the electron configuration with \(\text{Ar}\), another noble gas.
• \(\text{H}^-\) gains an electron to mirror the configuration of \(\text{He}\).

Because of their stability, noble gas configurations are often considered an ultimate goal for atoms undergoing electron transfer processes.

Ions and Charges

Ions form when atoms gain or lose electrons, leading to a charge due to the imbalance between protons and electrons. The charge of an ion is indicated by a positive (cation) or negative (anion) superscript following the element symbol.

• If an atom loses electrons, it becomes a cation with a positive charge, since there are now more protons than electrons. For example, \(\text{Na}\) loses one electron to become \(\text{Na}^+\).
• Conversely, gaining electrons results in an anion with a negative charge. This happens with \(\text{P}\), which gains three electrons to form \(\text{P}^{3-}\).

Ion formation is crucial in chemical bonding, as ions attract or repel based on their charged nature, leading to the formation of ionic compounds. Understanding how and why ions form can help explain the behavior of substances and guide predictions about their interactions.