Question

question 16 of 20
write the full electron configuration for a k⁻ ion.
electron configuration: 1s₂2s₂2p₆3s₂3p₆4s₂
incorrect answer
write the full electron configuration for an f⁻ ion.
electron configuration: 1s₂2s₂2p₆
incorrect answer

Explanation:

Step1: Determine the number of electrons

• For \(K^-\): Potassium (\(K\)) has an atomic number of \(19\). A \(K^-\) ion has \(19 + 1=20\) electrons.
• For \(F^-\): Fluorine (\(F\)) has an atomic number of \(9\). An \(F^-\) ion has \(9+ 1 = 10\) electrons.

Step2: Write the electron configuration using the Aufbau principle

• For \(K^-\):
• Fill \(1s\) first (\(1s^2\)), then \(2s\) (\(2s^2\)), then \(2p\) (\(2p^6\)), then \(3s\) (\(3s^2\)), then \(3p\) (\(3p^6\)), and finally \(4s\) (\(4s^2\)). But wait, after filling \(3p\), for \(20\) electrons, we have \(1s^22s^22p^63s^23p^64s^2\) is incorrect. Because after \(3p\), for \(K^-\) (which is isoelectronic with \(Ca\)), the correct full electron configuration is \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}\) is wrong. Wait no, \(K^-\) has \(20\) electrons. The correct electron configuration is \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}\) is actually correct for \(20\) electrons (but let's check again). Wait no, \(K^-\) is \(K + e^-\). \(K\) has electron configuration \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}\), adding one electron gives \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}\).
• For \(F^-\):
• Fill \(1s\) (\(1s^2\)), then \(2s\) (\(2s^2\)), then \(2p\). Since we have \(10\) electrons, \(2p\) can hold \(6\) electrons. So the electron configuration is \(1s^{2}2s^{2}2p^{6}\)

Answer:

• Electron configuration of \(K^-\): \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}\)
• Electron configuration of \(F^-\): \(1s^{2}2s^{2}2p^{6}\)