To determine whether selenium (Se) would form a cation or anion, you can start by drawing its Lewis dot structure. Selenium is in group 16 of the periodic table, which means it has six valence electrons. When drawing the Lewis dot structure, you would represent selenium with six dots around its symbol, indicating these valence electrons.
Selenium tends to gain two electrons in order to achieve a stable octet configuration, similar to the noble gases. This is because by gaining two electrons, selenium can fill its outer electron shell, making it more stable. When it gains these two electrons, selenium becomes negatively charged, forming an anion. The most common ion of selenium is the selenide ion (Se²⁻).
In contrast, if you were to consider the possibility of selenium losing electrons to form cations, it would likely be less stable due to the energy required to remove the six valence electrons. Therefore, based on the Lewis dot structure and the tendency of elements to gain or lose electrons to achieve stability, selenium is more inclined to form an anion rather than a cation.
In summary, by analyzing selenium’s Lewis dot structure and its behavior in terms of electron gain, it is clear that selenium commonly forms the selenide ion (Se²⁻) when it gains two electrons.