Compare the physical and chemical properties of the hydrides of each of the following elements: \(\mathrm{Na}\), \(\mathrm{Ca}, \mathrm{C}, \mathrm{N}, \mathrm{O}, \mathrm{Cl}\).

Ionic hydrides are compounds in which hydrogen is bonded with a metal of the first or second group of the periodic table, resulting in a release of one or two electrons and the formation of hydride ions (H^-).

For example, sodium hydride (NaH) comprises sodium ions (Na^+) and hydride ions, forming a crystalline solid structure. These hydrides are characterized by their high melting and boiling points, owing to the strong electrostatic forces between the ions in the lattice. Ionic hydrides are typically good conductors of heat and electricity in their molten state and are known to react vigorously with water, releasing hydrogen gas. This reaction highlights their strong basic nature, a property vital for various chemical syntheses and applications.

Covalent hydrides are formed when hydrogen atoms create covalent bonds with non-metal atoms, leading to a shared pair of electrons. Such compounds exhibit significantly diverse properties since they are based on the varying electronegativities and molecular structures of the constituent elements.

Methane (CH_4), ammonia (NH_3), water (H_2O), and hydrogen chloride (HCl) serve as classic examples. These hydrides can be gases, like methane and ammonia, or a liquid as in the case of water, which is a unique consequence of hydrogen bonding. Furthermore, their melting and boiling points are much lower compared to ionic or metallic hydrides. From a chemical standpoint, covalent hydrides like methane and ammonia are combustible, whereas water is non-combustible but exhibits slight ionization in solution, and hydrogen chloride is acidic, showcasing the diverse reactivity of these compounds.

Metallic hydrides are composed of hydrogen and a transition, post-transition, or actinide metal. In these compounds, hydrogen occupies interstitial sites within the metal lattice, allowing the metal atoms to maintain a metallic bonding character.

A prime example of metallic hydride is calcium hydride (CaH_2), where calcium donates electrons to hydrogen. These hydrides tend to be less conductive than their metal counterparts and have lower melting and boiling points than ionic hydrides. While they do react with water to release hydrogen gas, the reaction is less violent, indicating a less basic nature. Metallic hydrides are typically non-combustible and are often employed as hydrogen storage materials due to their capacity to reversibly absorb and release hydrogen gas.

The physical properties of hydrides, including state of matter, melting and boiling points, and density, mainly depend on the type of bonding they exhibit.

Ionic hydrides are usually high-density crystalline solids with high melting and boiling points due to the strong ionic bonds between the metal cations and hydride anions. Covalent hydrides, in contrast, might appear as gases, liquids, or low-melting solids, as the intermolecular forces are generally weaker, except in instances of hydrogen bonding which can elevate the boiling points significantly. Metallic hydrides also form solids, but with properties akin to their parent metals albeit usually less dense and with lower thermal stability compared to ionic hydrides.

The chemical properties of hydrides, such as reactivity with water, acidity or basicity, and combustibility, are highly influenced by their bonding nature.

Ionic hydrides show strong basicity and vigorously release hydrogen gas upon contact with water. Covalent hydrides exhibit a vast range of chemical behavior; for instance, methane is stable but combustible, while hydrogen chloride is acidic when dissolved in water. Metallic hydrides like CaH_2 react with water more slowly than ionic hydrides and are not as strongly basic. Understanding these properties is crucial for students as it allows them to predict the behavior of various hydrides in chemical reactions and their potential applications in industrial processes.