Which element/ion has this electron configuration: [1s22s22p63s23p6]+2 Group of answer choices argon (neutral) sulfur calcium ion chlorine potassium ion potassium (neutral)

The Correct Answer and Explanation is:

The correct answer is: calcium ion (Ca²⁺)


Explanation:

To determine which element or ion has the electron configuration [1s² 2s² 2p⁶ 3s² 3p⁶]⁺², we first count the total number of electrons in the configuration.

Let’s break it down:

  • 1s² → 2 electrons
  • 2s² → 2 electrons
  • 2p⁶ → 6 electrons
  • 3s² → 2 electrons
  • 3p⁶ → 6 electrons

Total = 2 + 2 + 6 + 2 + 6 = 18 electrons

Now we look at the periodic table to identify which neutral element has 20 electrons, because if an element has lost two electrons to form a +2 charge, it must have originally had 20 electrons in its neutral state. That element is calcium (Ca), which has an atomic number of 20.

So, when calcium becomes a Ca²⁺ ion, it loses two electrons. The two electrons lost are from the outermost shell, which in calcium’s case are the 4s electrons. The full electron configuration of neutral calcium is:
1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

When it loses two electrons to form Ca²⁺, the configuration becomes:
1s² 2s² 2p⁶ 3s² 3p⁶

This matches exactly the given configuration.


Why the other options are incorrect:

  • Argon (neutral): Argon has 18 electrons, and the configuration is the same, but it is neutral, not a +2 ion.
  • Sulfur: Has 16 electrons, so its neutral configuration is shorter than the one given.
  • Chlorine: Has 17 electrons, so also shorter than the given configuration.
  • Potassium (neutral): Has 19 electrons, so its configuration would include a 4s¹.
  • Potassium ion (K⁺): Has 18 electrons, and matches the configuration, but it is a +1 ion, not +2.

Thus, the correct match for the given configuration is calcium ion (Ca²⁺).

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