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A nitride ion is derived from a nitrogen atom, which is an element famously known for being crucial in both biology and atmospheric science. In its neutral state, nitrogen, located in Group 15 of the periodic table, possesses five valence electrons. However, when it gains three electrons, it forms the nitride ion, represented as \( \text{N}^{3-} \). This gain of electrons is critical as it fills its outer electron shell, leading to a stable configuration. The gaining of these electrons results in the nitride ion having a total of eight valence electrons. This is important because the valence electrons are the ones that participate in interactions with other atoms and ions. Understanding the concept of a nitride ion is foundational for exploring its chemical behavior and properties, especially in various compounds.

Valence electrons are the electrons located in the outermost shell of an atom. These electrons are vital since they determine how an atom interacts with others, playing a crucial role in the formation of chemical bonds. In the case of the nitrogen atom, it has five valence electrons in its neutral state. However, when nitrogen forms a nitride ion, it gains three additional electrons. This results in a total of eight valence electrons for the nitride ion. As a rule of thumb, elements aim to fill their outer electron shell to achieve stability, often following the octet rule, meaning they prefer to have eight electrons in their valence shell. This rule is significant in understanding the chemical behavior of elements, especially non-metals like nitrogen, as they tend to gain or share electrons during reactions to achieve such stability.

Calculating moles is fundamental in chemistry as it allows us to quantitatively understand the amount of a substance. The concept of moles connects the microscopic world of atoms and molecules to the macroscopic world we interact with. For nitrogen, with an atomic mass of approximately \( 14 \, \text{g/mol} \), we calculate moles by dividing the mass of the substance by its molar mass. In the example exercise, 4.2 grams of nitride ions are provided. To find the moles of \( \text{N}^{3-} \), the formula used is: \[ \text{Moles of } \text{N}^{3-} = \frac{4.2 \, \text{g}}{14 \, \text{g/mol}} = 0.3 \, \text{moles}. \] This result tells us that there are 0.3 moles of nitride ions in the sample. Understanding how to perform these calculations is essential when working with chemical equations and reactions.

The periodic table is a remarkable tool used by chemists as it organizes all the known elements according to their atomic number, electron configurations, and recurring chemical properties. Nitrogen, the precursor to the nitride ion, is found in Group 15. This group is characterized by having five valence electrons, a key aspect in defining their chemical behavior. Elements in the same group often exhibit similar chemical properties. Therefore, learning to navigate the periodic table not only helps in determining the properties of an element like nitrogen but also in predicting how it might behave in chemical reactions. The periodic trends, such as electronegativity, atomic size, and ionization energy, further aid in understanding the nature of elements like nitrogen and its ions.