Which of the following elements form +1 ions?
A sodium, magnesium, aluminum
B strontium, magnesium, calcium
C lithium, sodium, potassium
The Correct Answer and Explanation is:
The correct answer is C: lithium, sodium, potassium.
Explanation:
To understand why lithium (Li), sodium (Na), and potassium (K) form +1 ions, we need to look at their atomic structures and the general behavior of alkali metals in ion formation.
- Ion Formation and Electron Configuration:
- When atoms form ions, they do so by losing or gaining electrons to achieve a stable electron configuration. Most elements aim to attain the nearest noble gas configuration, which is stable.
- Group 1 elements (the alkali metals) all have one electron in their outermost shell. When these elements form ions, they tend to lose this single valence electron to achieve the electron configuration of the preceding noble gas. This process leaves them with a +1 charge, as they lose one negatively charged electron and have one more proton than electrons.
- Lithium (Li):
- The electron configuration of lithium is 1s² 2s¹. When lithium loses its single electron from the 2s orbital, it forms a Li⁺ ion with the electron configuration of helium (1s²), achieving stability.
- Sodium (Na):
- Sodium has the electron configuration 1s² 2s² 2p⁶ 3s¹. When sodium loses its single electron from the 3s orbital, it forms a Na⁺ ion with the electron configuration of neon (1s² 2s² 2p⁶), which is stable.
- Potassium (K):
- Potassium’s electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹. Upon losing its single electron from the 4s orbital, potassium forms a K⁺ ion with the electron configuration of argon (1s² 2s² 2p⁶ 3s² 3p⁶), achieving stability.
These elements (lithium, sodium, and potassium) are all alkali metals in Group 1 of the periodic table. They all follow the same pattern of forming +1 ions by losing their single valence electron, making answer C correct.
Why Not the Other Options?
- Option A (sodium, magnesium, aluminum):
- Magnesium (Mg) and aluminum (Al) do not form +1 ions. Magnesium, being in Group 2, forms Mg²⁺ ions by losing two electrons. Aluminum, in Group 13, forms Al³⁺ by losing three electrons.
- Option B (strontium, magnesium, calcium):
- Strontium (Sr) and calcium (Ca) are alkaline earth metals (Group 2) and form +2 ions by losing two electrons. Magnesium (Mg) forms a +2 ion as well. Therefore, this group does not form +1 ions.
Thus, only lithium, sodium, and potassium from Option C form +1 ions.