Question

How many of the following elements have 2 unpaired electrons in the ground state? C Te Hf Si

Answer 1

Answer:

• Option C) 3.

• C, Te, and Si have two unpaired electrons in the ground state.

Explanation:

You must draw the electron configuration.

C (carbon)

• Atomic number (Z): 12
• Number of electrons: 12
• Electron configuration of ground state, following Aufbau rules (filling orbitals in order of increasing energy):

        1s² 2s² 2p²

• Electron pairing following Hund's rules (fill different orbitals of same energy, with same spin, before adding a second electron, with opposite spin, to an orgital).

        1s² 2s² 2px↑ 2py↑

• As you see, these configuration shows two unpaired electrons (same spin) in the ground state.

Te (tellurium)

• Z = 52
• Number of electrons: 52
• Aufbau's rule and short notation: [Kr] 5s² 4d¹⁰ 5p⁴

• Hund's rule:  [Kr] 5s² 4d¹⁰ 5px↑↓ 5py↑ 5pz↑

• This configuration shows two unpaired elecctrons (same spin).

Hf (hafnium)

• Z = 72
• Number of electrons: 72
• Aufbau's rule and short notation: [Xe] 4f¹⁴ 5d²6s²
• This configuration shows that there are not unpaired electrons (the las orbital 6s is complete with 2 electrons)

Si (silicon)

• Z = 14
• Number of electrons: 14
• Aufbau's rule and short notation: [Ne] 3s² 3p²
• Hund's rule: [Ne] 3s² 3px↑ 3py↑
• This configuration shows two unpaired electrons.

Conclusion: C, Te and Si, have two unpaired electrons (same spin) in the ground state.