Hydrazine borane, \(\mathrm{NH}_{2} \mathrm{NH}_{2} \mathrm{BH}_{3}\), has been proposed as a hydrogen storage material. When reacted with lithium hydride (LiH), hydrogen gas is released: $$ \mathrm{NH}_{2} \mathrm{NH}_{2} \mathrm{BH}_{3}+\mathrm{LiH} \longrightarrow \mathrm{LiNH}_{2} \mathrm{NHBH}_{3}+\mathrm{H}_{2} $$ Write Lewis structures for \(\mathrm{NH}_{2} \mathrm{NH}_{2} \mathrm{BH}_{3}\) and \(\mathrm{NH}_{2} \mathrm{NHBH}_{3}^{-}\) and assign all formal charges.

Understanding the formal charge of an atom within a molecule is key to mastering chemical structures and reactions. The formal charge is the hypothetical charge the atom would have if we assume that electrons in all chemical bonds are shared equally between atoms, despite differences in electronegativity.

To calculate the formal charge on an atom, use the formula:
\[\text{Formal charge} = (\text{Valence electrons}) - \frac{1}{2}(\text{Bonded electrons}) - (\text{Lone pair electrons})\]
In the process of drawing Lewis structures, assigning formal charges helps us to verify the stability and likelihood of the molecule. It is a crucial step to predict the behavior of molecules during chemical reactions. For instance, a molecule with several high formal charges is likely less stable and more reactive.

Remember that the sum of the formal charges in a molecule should equal the overall charge of the molecule. This is a useful check to ensure that your calculations are on the right track. By paying close attention to the correct distribution of electrons in your Lewis structures, you can accurately calculate the formal charges, as seen in the example of hydrazine borane and its reaction product.

Valence electrons play a pivotal role in forming chemical bonds and determining the chemical properties of elements. They are the outermost electrons of an atom and are involved in the interactions that lead to the formation of molecules.

When drawing Lewis structures, it's essential to know the number of valence electrons for each element involved. To impart a clearer understanding:

• Hydrogen and elements in Group 1 have 1 valence electron.
• Group 2 elements have 2 valence electrons.
• Groups 13 to 18 (excluding Helium) have 3 to 8 valence electrons, respectively, following the pattern of their group numbers minus 10. For example, Carbon in Group 14 has 4 valence electrons.

Chemical reactions often involve the exchange or sharing of valence electrons, and the octet rule states that atoms tend to bond in ways that give them eight valence electrons, resembling the electron configuration of a noble gas. However, there are exceptions to this rule, such as Boron, which is comfortable with six valence electrons, as seen in the exercise's initial molecule, \(\mathrm{NH}_{2} \mathrm{NH}_{2} \mathrm{BH}_{3}\).

Exploring materials for efficient hydrogen storage is crucial for advancing clean energy technologies. Hydrazine borane, mentioned in the exercise, is one such material that captures attention for its potential to release hydrogen upon reacting with lithium hydride.

Hydrogen storage materials are evaluated based on several parameters, including gravimetric and volumetric storage densities, release temperatures, and reversibility of hydrogen uptake. The ideal material must securely store hydrogen but also release it readily when needed without degradation of the storage medium.

In the context of the reaction presented, the reaction between hydrazine borane and lithium hydride forms lithium amide and a derivative of borane, along with the liberation of hydrogen gas. This exemplifies a type of chemical hydrogen storage. Such materials are significant in developing hydrogen as a sustainable energy source, particularly for mobile applications like fuel cells in vehicles and as a means to balance intermittent renewable energy sources.