What is the identity of the element X in the following ions? (a) X2+, a cation that has 36 electrons (b) X-, an anion that has 36 electrons

Key Concepts

Atomic Number and Electrons

The atomic number of an element is defined as the number of protons in its nucleus, which also equals the number of electrons in a neutral atom. In this question, the identity of element X can be determined by analyzing the number of electrons in its ionic forms. For X2+, having 36 electrons indicates it originally had 38 protons, while X-, with 36 electrons, suggests it originally had 35 protons.

Ionic Charge

Ionic charge refers to the electrical charge that an atom or molecule carries due to the loss or gain of electrons. A cation, like X2+, has a positive charge due to the loss of electrons, while an anion, like X-, has a negative charge due to the gain of electrons. Understanding how these charges relate to the number of electrons helps in identifying the element's identity based on its ionic forms.

Periodic Table and Element Identity

The periodic table organizes elements based on their atomic number and properties. Each element has a unique atomic number that corresponds to its identity. In this case, the element with an atomic number of 36 is krypton (Kr), which can be confirmed by recognizing that X2+ and X- correspond to the same element with different electron configurations, leading to the conclusion that X is krypton.