Chapter 3: Problem 33
Identify the least stable ion amongst the following: (a) \(\mathrm{Li}^{-}\) (b) \(\mathrm{Be}\) (c) \(\mathrm{B}^{-}\) (d) \(\mathrm{C}^{-}\)
Short Answer
Expert verified
The least stable ion is \(\mathrm{Li}^-\).
Step by step solution
01
Review Electron Configurations
First, analyze the electron configurations of the provided ions or elements. - For \(\mathrm{Li}^-\), the atomic number is 3, so the configuration is \(1s^2 2s^2\) due to the added electron.- \(\mathrm{Be}\) has an atomic number of 4, with the configuration \(1s^2 2s^2\).- \(\mathrm{B}^-\) has an atomic number of 5, adjusted to \(1s^2 2s^2 2p^2\).- \(\mathrm{C}^-\) has an atomic number of 6, adjusted to \(1s^2 2s^2 2p^3\).
02
Consider the Octet Rule
Next, assess the stability of each species based on the octet rule, which suggests that atoms tend to be more stable when they have eight electrons in their valence shell.- \(\mathrm{Li}^-\) has only two valence electrons.- \(\mathrm{Be}\) has two valence electrons.- \(\mathrm{B}^-\) has three valence electrons, one less than the stable octet configuration. - \(\mathrm{C}^-\) gets closer to satisfying the octet with five electrons.
03
Evaluate Stability Based on Charge
Now, examine how the charge affects stability. Negative ions are typically unstable if they leave a neutral atom with fewer than a full valence shell.- \(\mathrm{Li}^-\) is unstable because adding an electron makes the already stable neutral atom unstable.- \(\mathrm{B}^-\) gains some stability from an additional electron, but it still lacks a full octet.- \(\mathrm{C}^-\), although negatively charged, moves closer to octet fulfillment, offering some stability despite the charge.
04
Identify the Least Stable Ion
Considering the above factors, \(\mathrm{Li}^-\) stands out as the least stable due to the repulsion and unsuitable electron configuration that results from adding an electron to an already stable \(\mathrm{Li}\) atom that follows the duet rule. This leads to high instability.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Electron Configuration
Electrons are arranged around the nucleus of an atom in specific ways, known as electron configurations. This configuration describes the distribution of electrons among different energy levels and subshells. Understanding the electron configuration is crucial because it reveals essential details of atom and ion stability.
Each element in the periodic table has a unique electron configuration. For example, lithium \(\mathrm{Li}^-\) begins with three protons and three electrons, so its neutral electron configuration is \(1s^2 2s^1\). When it gains an extra electron to become \(\mathrm{Li}^-\), the configuration changes to \(1s^2 2s^2\).
On the other hand, the electron configuration of \(\mathrm{Be}\) remains \(1s^2 2s^2\), without any net charge. Beryllium is stable in its neutral form because it fills the energy level efficiently. Similarly, ions like \(\mathrm{B}^-\) and \(\mathrm{C}^-\) need adaptations. \(\mathrm{B}^-\) modifies to \(1s^2 2s^2 2p^2\) to accommodate the extra electron.
Knowing these configurations helps understand which electrons are occupying the outermost shell, offering insights into how atoms will behave in reactions.
Each element in the periodic table has a unique electron configuration. For example, lithium \(\mathrm{Li}^-\) begins with three protons and three electrons, so its neutral electron configuration is \(1s^2 2s^1\). When it gains an extra electron to become \(\mathrm{Li}^-\), the configuration changes to \(1s^2 2s^2\).
On the other hand, the electron configuration of \(\mathrm{Be}\) remains \(1s^2 2s^2\), without any net charge. Beryllium is stable in its neutral form because it fills the energy level efficiently. Similarly, ions like \(\mathrm{B}^-\) and \(\mathrm{C}^-\) need adaptations. \(\mathrm{B}^-\) modifies to \(1s^2 2s^2 2p^2\) to accommodate the extra electron.
Knowing these configurations helps understand which electrons are occupying the outermost shell, offering insights into how atoms will behave in reactions.
Octet Rule
The octet rule is a cornerstone in understanding chemical stability. It postulates that atoms are most stable when they have eight electrons in their outer valence shell, akin to the electron configuration of noble gases.
According to this principle, atoms will gain, lose, or share electrons to satisfy the octet rule. For example, \(\mathrm{Li}^-\) fails to achieve stability because it adds an electron to an already stable configuration. Conversely, \(\mathrm{C}^-\) gets closer to a filled valence shell but still falls short of the octet.
Elements like \(\mathrm{Be}\) and \(\mathrm{B}^-\) also strive towards this signature stability. Boron's \(\mathrm{B}^-\), with its electronic adjustment, leads it to \(1s^2 2s^2 2p^2\), which is just short of the octet goal. Meanwhile, beryllium's configuration is neither seeking nor achieving octet as it remains neutral.
Recognizing how closely elements meet the octet rule can predict which ions are stable and which ones will react to form new compounds or configurations.
According to this principle, atoms will gain, lose, or share electrons to satisfy the octet rule. For example, \(\mathrm{Li}^-\) fails to achieve stability because it adds an electron to an already stable configuration. Conversely, \(\mathrm{C}^-\) gets closer to a filled valence shell but still falls short of the octet.
Elements like \(\mathrm{Be}\) and \(\mathrm{B}^-\) also strive towards this signature stability. Boron's \(\mathrm{B}^-\), with its electronic adjustment, leads it to \(1s^2 2s^2 2p^2\), which is just short of the octet goal. Meanwhile, beryllium's configuration is neither seeking nor achieving octet as it remains neutral.
Recognizing how closely elements meet the octet rule can predict which ions are stable and which ones will react to form new compounds or configurations.
Ion Charge Effects
Ion charge plays a pivotal role in the stability of ions. Positive or negative charges can alter the stability of an atom. When an atom becomes a positive ion by losing electrons, its stability can often increase, especially if it moves closer to a noble gas configuration.
However, when ions gain electrons and become negatively charged, as seen in \(\mathrm{Li}^-\), their stability can decrease if the new configuration introduces electron-electron repulsion without fulfilling valence shell completion. \(\mathrm{Li}^-\) is a clear example, where the additional electron results in instability.
In contrast, \(\mathrm{C}^-\), which also bears a negative charge but has a more favorable electron configuration closer to the octet, exhibits greater stability compared to \(\mathrm{Li}^-\). Negative charges can confer stability if they accompany near-complete valence shells.
Understanding the influence of ion charges helps predict how certain ion forms might result in increased or decreased stability based on electron configurations.
However, when ions gain electrons and become negatively charged, as seen in \(\mathrm{Li}^-\), their stability can decrease if the new configuration introduces electron-electron repulsion without fulfilling valence shell completion. \(\mathrm{Li}^-\) is a clear example, where the additional electron results in instability.
In contrast, \(\mathrm{C}^-\), which also bears a negative charge but has a more favorable electron configuration closer to the octet, exhibits greater stability compared to \(\mathrm{Li}^-\). Negative charges can confer stability if they accompany near-complete valence shells.
Understanding the influence of ion charges helps predict how certain ion forms might result in increased or decreased stability based on electron configurations.
Valence Electrons
Valence electrons are the electrons located in the outermost shell of an atom. They hold significant importance as they determine an atom's chemical properties, including reactivity and bonding capacity.
An atom's pursuit to achieve a stable electronic configuration relies heavily on these valence electrons. Atoms with incomplete valence shells tend to be more reactive, as they seek to gain or lose electrons to arrive at a stable state. \(\mathrm{Li}^-\), with only two electrons in its outer shell when neutral, finds added electrons disruptive.
On the contrary, \(\mathrm{C}^-\)'s five valence electrons set it closer to stability, thus making it more stable than \(\mathrm{Li}^-\). Beryllium, with its neutral valence configuration, doesn't seek extra electrons, showcasing its stability in the elemental form.
Considering valence electrons is essential as it can highlight an element's tendency to form compounds, especially revealing when there is a marked difference in electron affinity or electronegativity.
An atom's pursuit to achieve a stable electronic configuration relies heavily on these valence electrons. Atoms with incomplete valence shells tend to be more reactive, as they seek to gain or lose electrons to arrive at a stable state. \(\mathrm{Li}^-\), with only two electrons in its outer shell when neutral, finds added electrons disruptive.
On the contrary, \(\mathrm{C}^-\)'s five valence electrons set it closer to stability, thus making it more stable than \(\mathrm{Li}^-\). Beryllium, with its neutral valence configuration, doesn't seek extra electrons, showcasing its stability in the elemental form.
Considering valence electrons is essential as it can highlight an element's tendency to form compounds, especially revealing when there is a marked difference in electron affinity or electronegativity.
