Question

Write electron configurations for the most stable ion formed by each of the elements Te, \(\mathrm{Cl}, \mathrm{Sr},\) and \(\mathrm{Li}\) (when in stable ionic compounds).

Short answer

The electron configurations for the most stable ions are: Te: \(Te^{2-}: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6\) Cl: \(Cl^-: 1s^2 2s^2 2p^6 3s^2 3p^6\) Sr: \(Sr^{2+}: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6\) Li: \(Li^+: 1s^2\)

Step-by-step solution

Neutral Electron Configurations

For each element, write the electron configuration in their neutral states. 1. Te (Tellurium - atomic number 52): Using the periodic table, we find the electron configuration as: \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^4\] 2. Cl (Chlorine - atomic number 17): Electron configuration for chlorine is: \[1s^2 2s^2 2p^6 3s^2 3p^5\] 3. Sr (Strontium - atomic number 38): Electron configuration for strontium is: \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2\] 4. Li (Lithium - atomic number 3): Electron configuration for lithium is: \[1s^2 2s^1\]

Determine the Most Stable Ions

Determine the most stable ion for each element by identifying the electron configuration that achieves the nearest noble gas configuration. 1. Te: Tellurium needs to gain 2 electrons to achieve the noble gas configuration of Xenon. Thus, its most stable ion is Te with a charge of -2: \(Te^{2-}\). 2. Cl: Chlorine needs to gain 1 electron to achieve the noble gas configuration of Argon. Thus, its most stable ion is Cl with a charge of -1: \(Cl^-\). 3. Sr: Strontium needs to lose 2 electrons to achieve the noble gas configuration of Krypton. Thus, its most stable ion is Sr with a charge of +2: \(Sr^{2+}\). 4. Li: Lithium needs to lose 1 electron to achieve the noble gas configuration of Helium. Thus, its most stable ion is Li with a charge of +1: \(Li^+\).

Write the Electron Configurations of the Most Stable Ions

Write the electron configurations for the most stable ions of each element. 1. \(Te^{2-}\) (Tellurium): \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6\] (Xenon configuration) 2. \(Cl^-\) (Chlorine): \[1s^2 2s^2 2p^6 3s^2 3p^6\] (Argon configuration) 3. \(Sr^{2+}\) (Strontium): \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6\] (Krypton configuration) 4. \(Li^+\) (Lithium): \[1s^2\] (Helium configuration) The electron configurations for the most stable ions are: Te: \(Te^{2-}: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6\) Cl: \(Cl^-: 1s^2 2s^2 2p^6 3s^2 3p^6\) Sr: \(Sr^{2+}: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6\) Li: \(Li^+: 1s^2\)

Key concepts

Stable Ions

Understanding what makes an ion stable is crucial in chemistry. Stable ions are charged particles that have achieved a complete outer shell of electrons, very similar to the electron configurations of noble gases. To reach stability, atoms will either gain or lose electrons to fill or empty their outer shell. This endeavor to reach a noble gas-like arrangement is due to the octet rule, which suggests that atoms are most stable when they have eight electrons in their valence shell, mirroring the electron configuration of noble gases.

For example, when chlorine (Cl) gains one electron, it forms a chloride ion (Cl^-) with a complete outer shell identical to argon, a noble gas. On the other hand, metals like lithium (Li) lose electrons to achieve stability; Li⁺ has lost one electron, resembling the noble gas helium. Transition metals may exhibit more complex behaviors due to their d and f orbitals, however, the underlying objective remains the same: attain a stable electron arrangement.

Noble Gas Configuration

The noble gas configuration represents the ultimate goal for non-noble elements seeking chemical stability. Noble gases have a full valence shell, which makes them unusually stable and mostly inert. Atoms form ions to replicate this stability. Negative ions (anions) are formed by non-metals gaining electrons, whereas positive ions (cations) are formed by metals losing electrons.

Ions that achieve a noble gas configuration have particularly low energy and high stability. As seen in the textbook problem, tellurium (Te) acquires a 2- charge by gaining two electrons, simulating the electron configuration of the noble gas xenon (Xe). By achieving noble gas configurations, ions minimize their potential energy, making this state highly favored in nature.

Periodic Table

The periodic table is an invaluable tool for chemists, serving as a roadmap for understanding atomic structure and predicting how elements will react to form compounds. The table is organized by increasing atomic number and is arranged in a way that groups elements with similar properties together. For instance, all noble gases are located in group 18, exhibiting full valence shells and stability.

When working out electron configurations and predicting stable ions, the periodic table allows us to determine the number of valence electrons an element has and thus how many electrons it needs to lose or gain to achieve a noble gas configuration. As such, the periodic table is not just a list of elements but a framework that helps anticipate the formation of ions, guide the writing of electron configurations, and understand chemical reactivity.