* Smaller size and higher charge density of beryllium: Beryllium is a much smaller atom than barium. This means the positive charge of the beryllium ion is concentrated over a smaller area, creating a higher charge density. This strong positive charge attracts the electron cloud of chlorine more effectively, leading to a greater degree of covalent character.
* Higher electronegativity difference: The electronegativity difference between beryllium and chlorine is smaller than that between barium and chlorine. This difference is a measure of the tendency of an atom to attract electrons. A smaller electronegativity difference indicates a more covalent character.
* Polarizability of the cation: Beryllium ion (Be²⁺) is much more polarizable than barium ion (Ba²⁺). This means that the electron cloud of beryllium can be more easily distorted by the negative charge of the chlorine ion, leading to a greater degree of covalent character.
In summary, the smaller size, higher charge density, and greater polarizability of beryllium, combined with the smaller electronegativity difference between beryllium and chlorine, contribute to the more covalent character of beryllium chloride compared to barium chloride.
Note: It's important to remember that the concept of "ionic" or "covalent" is often a spectrum, and many compounds exhibit characteristics of both. While beryllium chloride exhibits more covalent character, it's not strictly a covalent compound, and still possesses some ionic properties.
