An element's most stable ion forms an ionic compound with chlorine having the formula XCl₂. If the ion of element X has a mass of 89 and 36 electrons, what is the identity of the element, and how many neutrons does it have?

Question

Quizplus · Accepted Answer

Sr, 51 neutrons. The ion of element X has 36 electrons, which means it must have lost electrons to form a positive ion. The neutral atom would have more protons than the ion has electrons. Since the ion has 36 electrons, it matches the electron count of krypton (Kr), which is a noble gas. However, the element that loses electrons to match krypton's electron configuration is strontium (Sr), which has 38 protons. The mass of the ion is 89, which is the mass number of strontium. The number of neutrons is calculated by subtracting the atomic number (number of protons) from the mass number: 89 - 38 = 51 neutrons.

An Element's Most Stable Ion Forms an Ionic Compound with Chlorine