A calcium ion (+2 charge) has how many electrons?
a) 18 electrons b) 20 electrons c) 22 electrons d) 24 electrons
The Correct Answer and Explanation is:
The correct answer is a) 18 electrons.
To understand why, we need to consider the basic structure of an atom and the concept of ion formation.
- Atomic Structure: A calcium atom (Ca) has 20 protons and 20 electrons in its neutral state. This is because the number of protons, which determines the atomic number of an element, is equal to the number of electrons in a neutral atom to balance the positive charge of protons with the negative charge of electrons. Therefore, a neutral calcium atom has 20 electrons.
- Formation of a Calcium Ion (Ca²⁺): When a calcium atom loses two electrons, it becomes a calcium ion with a +2 charge. This is a typical behavior for alkaline earth metals like calcium, which readily lose electrons to achieve a more stable electron configuration, usually similar to the nearest noble gas.
- Electron Configuration of Ca²⁺:
- The neutral calcium atom (Ca) has an electron configuration of 1s² 2s² 2p⁶ 3s² 3p⁶ 4s².
- When it loses two electrons to form a Ca²⁺ ion, these electrons are lost from the outermost energy level (4s²).
- The resulting electron configuration for the Ca²⁺ ion is 1s² 2s² 2p⁶ 3s² 3p⁶, which is identical to the electron configuration of argon (Ar), a noble gas. This is a stable configuration because argon has a full octet in its outer shell, making it chemically inert.
- Conclusion: Since the calcium ion (Ca²⁺) has lost two electrons from its original 20 electrons, it now has 18 electrons. Therefore, the correct answer is a) 18 electrons. This loss of electrons results in a net positive charge of +2, which is characteristic of the Ca²⁺ ion.