How many electrons does a selenide ion (Se2- ) have?
The correct answer and explanation is:
The selenide ion (Se²⁻) has 36 electrons.
Selenium (Se) is a chemical element with the atomic number 34. This means a neutral selenium atom has 34 protons in its nucleus and, correspondingly, 34 electrons surrounding the nucleus to balance the positive charge of the protons. When selenium forms an ion, it gains or loses electrons to achieve a more stable electronic configuration, often resembling the nearest noble gas.
In the case of the selenide ion, selenium gains two extra electrons. These additional electrons give the ion a negative charge of 2- because the number of electrons (negative charges) exceeds the number of protons (positive charges) by two. This gain of two electrons increases the total electron count from 34 to 36.
This electron gain occurs because selenium’s electron configuration allows it to achieve a full outer shell, resembling the noble gas krypton, which has 36 electrons. Achieving this stable electronic configuration lowers the energy of the ion and makes it more stable chemically.
Thus, the selenide ion has the same number of electrons as the noble gas krypton. The addition of two electrons changes selenium from a neutral atom with 34 electrons to an ion with 36 electrons. This extra negative charge influences the ion’s chemical properties, such as its ability to form ionic compounds with positively charged ions (cations), like sodium (Na⁺) or calcium (Ca²⁺).
In summary, the selenide ion has 36 electrons, which is the original 34 electrons of neutral selenium plus 2 additional electrons that give the ion its 2- charge.