Calcium nitride is an inorganic compound formed by the chemical combination of the metallic element calcium and the non-metallic element nitrogen. It is classified as an ionic compound, held together by strong electrostatic forces between positively and negatively charged ions. Determining the formula requires examining the electrical charges of its constituent atoms.
Determining the Ionic Charges
The charge an atom takes relates directly to its position on the periodic table. Calcium (Ca) is an alkaline earth metal in Group 2, readily giving up its two outermost valence electrons. Losing these electrons forms a cation with a positive charge of +2, represented as Ca\(^{2+}\). Nitrogen (N), found in Group 15, prefers to gain electrons to fill its outer energy shell. It requires three electrons to achieve a stable configuration, forming the nitride anion. This ion carries a negative charge of -3, written as N\(^{3-}\). The final chemical formula must achieve electrical neutrality by balancing the total positive charge from the calcium ions with the total negative charge from the nitride ions.
Deriving the Chemical Formula
The formula for calcium nitride requires finding the smallest whole number ratio of Ca\(^{2+}\) ions and N\(^{3-}\) ions that results in a net charge of zero. Since the charges are +2 and -3, the least common multiple of their absolute values (2 and 3) is 6. This means the total positive charge must be +6, and the total negative charge must be -6. To reach a total positive charge of +6, three calcium ions are needed (3 x +2 = +6). To achieve the necessary total negative charge of -6, two nitride ions are required (2 x -3 = -6). Combining these ions in a three-to-two ratio results in the final, electrically neutral compound. Therefore, the chemical formula for calcium nitride is Ca\(_3\)N\(_2\).
Physical Properties and Applications
Calcium nitride is a brown to red-brown crystalline powder. It is a relatively refractory material, possessing a high melting point around 1195°C, which makes it suitable for high-temperature environments. A primary characteristic is its high reactivity with water. When exposed to moisture, calcium nitride reacts vigorously to produce calcium hydroxide and release ammonia gas. This compound is utilized in specialized industrial processes, such as a source of nitride ions for producing complex nitrides and specific optical ceramics. It also finds use in the manufacture of high-end phosphors for light-emitting diodes (LEDs).