How does the nature of hydrides change across the periodic table?

The nature of hydrides changes across the periodic table in terms of bonding, structure, and reactivity.

As we move across the periodic table, the nature of hydrides changes significantly. This is primarily due to the differences in electronegativity, atomic size, and the number of valence electrons of the elements involved.

Starting with Group 1 (alkali metals), these elements form ionic hydrides. These hydrides are formed when hydrogen reacts with metals, resulting in a positive hydrogen ion (H+). The hydrides are typically white crystalline solids that are highly reactive, especially with water. They have high melting and boiling points due to the strong electrostatic forces of attraction between the ions.

Moving to Group 14 (carbon group), these elements form covalent hydrides. In these hydrides, hydrogen shares its electron with the other element to form a covalent bond. These hydrides can exist as gases, liquids, or solids at room temperature, depending on the size and structure of the molecules. They are less reactive than ionic hydrides and have lower melting and boiling points due to the weaker intermolecular forces.

Lastly, in Groups 15 to 17 (nitrogen, oxygen, and halogen groups), the elements form covalent hydrides that are polar in nature. This is because the electronegativity difference between hydrogen and these elements is significant, leading to an uneven distribution of electron density and creating a dipole. These hydrides are generally gases at room temperature and are more reactive than the covalent hydrides of Group 14.

In summary, the nature of hydrides changes across the periodic table from ionic to covalent, with varying degrees of polarity and reactivity. This is influenced by the properties of the elements they are formed with, including electronegativity, atomic size, and the number of valence electrons. Understanding these changes can help predict the properties and behaviour of hydrides, which is crucial in many areas of chemistry.