How many lone pairs of electrons are on the Se atom
The correct answer and explanation is:
Correct Answer: 1 lone pair
Explanation (300 words):
To determine the number of lone pairs of electrons on a selenium (Se) atom, we start by looking at selenium’s position on the periodic table.
Selenium (Se) is in Group 16, which means it has 6 valence electrons. Elements in Group 16 include oxygen, sulfur, selenium, tellurium, and polonium, all of which have similar electron configurations in their outermost shell.
Let’s focus on a neutral Se atom, not in a compound. Its electron configuration is:
[Ar] 3d¹⁰ 4s² 4p⁴
This shows that Se has 2 electrons in the 4s orbital and 4 electrons in the 4p orbital — a total of 6 valence electrons.
Visualizing the electron distribution:
- The 4s orbital contains 2 electrons (completely filled).
- The 4p orbital can hold 6 electrons, but Se only has 4 electrons there.
- In orbital notation, these 4 electrons occupy the 3 p-orbitals as follows: one orbital gets two paired electrons, and the other two orbitals get one unpaired electron each.
Thus, of the 6 valence electrons:
- 4 are involved in bonding or are unpaired.
- The remaining 2 electrons form 1 lone pair.
So, on a neutral Se atom, there is 1 lone pair of electrons.
In molecules:
In compounds like selenium dioxide (SeO₂) or selenic acid (H₂SeO₄), the number of lone pairs may change depending on bonding and hybridization. However, when asked how many lone pairs are on the Se atom alone (as an isolated atom), the answer is based solely on its valence electron configuration.
Summary:
Selenium has 6 valence electrons. After accounting for electrons that may be used for bonding, 1 lone pair remains on the selenium atom in its elemental state.