Atomic Physics

Beryllium ( ) has an atomic number of 4, and its electron configuration is . In , beryllium forms two covalent bonds with two chlorine atoms. To achieve this, the orbital and one orbital of beryllium mix to form two hybrid orbitals. These hybrid orbitals are linear and oriented at an angle of , consistent with the linear geometry of .

The two hybrid orbitals of beryllium overlap with the unpaired electrons of chlorine atoms to form two sigma ( ) bonds. This results in a linear molecular geometry for .

Final Answer: The type of hybrid orbital present at the beryllium atom in is , which corresponds to option .

Step 1: Recall Dobereiner's law of triads.

Dobereiner's law of triads states that when elements are arranged in increasing order of atomic weight, the atomic weight of the middle element in a triad is approximately the average of the atomic weights of the first and third elements.

Step 2: Apply the law to the given data.

The atomic weights of lithium ( ) and potassium ( ) are 7 and 39, respectively. Sodium ( ) lies between them in the triad. Using the formula:

Substitute the values:

Final Answer: The atomic weight of sodium is , which corresponds to option .