Question

Which of the following statements regarding hydrides is not correct? (a) lonic hydrides are crystalline, non-volatile and non-conducting in solid state. (b) Electron-deficient hydrides act as Lewis acids or electron acceptors. (c) Elements of group-13 form electron-deficient hydrides. (d) Elements of group \(15-17\) form electron-precise hydrides.

Short answer

Statement (d) is not correct because while group 15 elements form electron-precise hydrides, group 16 and 17 elements form electron-rich hydrides.

Step-by-step solution

Understanding Ionic Hydrides

Ionic hydrides are formed by alkali metals and alkaline earth metals reacting with hydrogen. These compounds are ionic in nature, generally crystalline, non-volatile, and do not conduct electricity in solid form because the ions are not free to move.

Identifying Electron-deficient Hydrides

Electron-deficient hydrides have fewer electrons than required for forming conventional covalent bonds. They are formed by elements from group 13, for instance, boron and aluminum hydrides. These compounds tend to accept electrons and hence act as Lewis acids.

Assessing Group 13 Element Hydrides

Group 13 elements like B, Al, Ga form electron-deficient hydrides due to their ability to accept electrons to complete their octet, which corresponds with what is stated in options (b) and (c).

Analyzing Electron-precise Hydrides

Electron-precise hydrides are formed by elements that have enough electrons to form the required number of covalent bonds without any electrons left over or any deficiency. Elements of group 15, like nitrogen, form such compounds, e.g., ammonia (NH3).

Examining Electron-precise Hydrides for Group 15-17

While group 15 elements do indeed form electron-precise hydrides, group 16 and 17 elements (like oxygen and fluorine) form electron-rich hydrides such as water (H2O) and hydrogen fluoride (HF), which have lone pairs of electrons.

Determining Incorrect Statement

Since group 15 elements form electron-precise hydrides but group 16 and 17 do not, statement (d) is incorrect. Groups 16 and 17 form hydrides that are electron-rich and not electron-precise.

Key concepts

Ionic Hydrides

Ionic hydrides are a fascinating category of compounds typically formed when alkali metals or alkaline earth metals react with hydrogen. Think of them as the result of a simple dance between positively charged metal cations and negatively charged hydride anions (H−). What's really interesting is that, despite being ionic, these hydrides don't exhibit electrical conductivity in their solid state. This is because in a crystalline structure, ions are fixed in place and can't flow to conduct electricity. These substances are also non-volatile, meaning they don't vaporize easily, making them quite stable and safe to handle under normal laboratory conditions.

It's important for students to grasp that while ionic hydrides do not conduct electricity in their solid form, they can conduct when melted or dissolved in water, turning into conducting electrolytes as ions become free to move. This behavior is a key cornerstone of understanding ionic compounds in general.

Electron-Deficient Hydrides

Electron-deficient hydrides might sound like something is missing, and that's exactly the case! These compounds have fewer electrons than they would need to form standard covalent bonds. Picture a group of friends where there aren't enough snacks to go around – some friends aren't going to be too happy! Similarly, electron-deficient hydrides are in a constant search for extra electrons to feel complete. Found commonly within group 13 elements - think boron (B) and aluminum (Al) - these hydrides are always looking to accept electrons to fill their 'snack tray' and complete their octet. This accepting behavior makes them act like Lewis acids – a key term in chemistry that refers to substances ready to accept electron pairs. Therefore, understanding electron-deficient hydrides allows students to better understand the concept of Lewis acids and their role in chemical reactions.

Moreover, recognizing electron-deficient hydrides explains their reactivity and provides insights into their role in various industrial processes, such as in the creation of complex chemical structures through hydride transfer reactions.

Electron-Precise Hydrides

Moving on from scarcity to just the right amount, we have electron-precise hydrides. These compounds are the Goldilocks of the hydride world – they have precisely the right number of electrons to form perfect covalent bonds with no extras or shortages. These atoms don't need to share with their neighbors or take from others; they have enough electrons to go around and complete full electron shells. Group 15 is a prime example of this category, with nitrogen forming ammonia (NH3) as a well-known electron-precise hydride.

Understanding electron-precise hydrides offers clarity on molecular structures and reactivity, especially when it comes to predicting how these substances may behave in different chemical environments. It's also key for grasping the stability of certain compounds, as an exact match between electrons and bonding capacity leads to a stable and happy molecule, much like a puzzle that has been perfectly pieced together.

Lewis Acids

Lastly, let’s demystify Lewis acids, which are often a source of confusion for students. To understand a Lewis acid, think of it not in terms of the usual acid-base reaction with protons but as a compound or ion that is eager to snap up a pair of electrons. Yes, like a corporate headhunter, a Lewis acid is on the prowl for valuable electrons to hire into their empty orbital positions. This definition broadens the scope of acid-base chemistry and includes electron-deficient species, even those without hydrogen, such as boron trifluoride (BF3).

Lewis acids play vital roles not only in theoretical chemistry but also in industrial applications, such as in catalysts that speed up reactions. By understanding this concept, students gain insight into a myriad of chemical reactions, particularly those involving coordination compounds where a central metal ion (a Lewis acid) pairs with ligands (electron pair donors).