A major challenge in implementing the 'hydrogen economy' is finding a safe, lightweight, and compact way of storing hydrogen for use as a fuel. The hydrides of light metals are attractive for hydrogen storage because they can store a high weight percentage of hydrogen in a small volume. For example, NaAlH4 can release 5.6% of its mass as H2 upon decomposing to NaH(s), Al(s), and H2(g). NaAlH4 possesses both covalent bonds, which hold polyatomic anions together, and ionic bonds. (b) Which element in NaAlH4 is the most electronegative? Which one is the least electronegative? Which element in NaAlH4 is the least electronegative?

Verified step by step guidance

1. 1. To determine the most and least electronegative elements in NaAlH4, we need to refer to the periodic table. Electronegativity is a measure of the ability of an atom to attract electrons. It increases from left to right across a period and decreases from top to bottom within a group.
2. 2. In the compound NaAlH4, we have the elements Sodium (Na), Aluminum (Al), and Hydrogen (H).
3. 3. Looking at the periodic table, we can see that Hydrogen (H) is the most electronegative element among these three. This is because it is located at the top right of the periodic table (excluding the noble gases).
4. 4. On the other hand, Sodium (Na) is the least electronegative element in NaAlH4. This is because it is located at the far left of the periodic table, where electronegativity values are the lowest.
5. 5. Therefore, Hydrogen (H) is the most electronegative element and Sodium (Na) is the least electronegative element in the compound NaAlH4.

Key Concepts

Electronegativity

Electronegativity is a measure of an atom's ability to attract and hold onto electrons in a chemical bond. It is a key factor in determining the nature of bonds formed between atoms, influencing molecular polarity and reactivity. The Pauling scale is commonly used to quantify electronegativity, with fluorine being the most electronegative element.

Covalent and Ionic Bonds

Covalent bonds occur when two atoms share electrons, typically between nonmetals, leading to the formation of molecules. In contrast, ionic bonds form when one atom donates electrons to another, resulting in the attraction between positively and negatively charged ions. Understanding these bond types is crucial for analyzing the structure and properties of compounds like NaAlH4.

Hydrides

Hydrides are compounds formed between hydrogen and other elements, often metals. They can exist in various forms, including ionic and covalent hydrides, and are significant in hydrogen storage technologies. Light metal hydrides, such as NaAlH4, are particularly noted for their ability to absorb and release hydrogen gas, making them valuable for applications in the hydrogen economy.