Which of the following represents the correct Lewis dot structure for selenium (Se)? Select one:
The Correct Answer and Explanation is:
The correct answer is b.
The Lewis dot structure is a diagram that shows the valence electrons of an atom. Valence electrons are the electrons in the outermost energy shell of an atom, and they are the electrons that participate in chemical bonding. To determine the correct Lewis structure for selenium (Se), we must first find the number of valence electrons it possesses.
The number of valence electrons for a main-group element can be easily determined from its position on the periodic table. Selenium (Se) is located in Group 16 of the periodic table. Elements in this group, which also includes oxygen and sulfur, all have six valence electrons. This can also be confirmed by looking at selenium’s electron configuration, [Ar] 3d¹⁰ 4s²4p⁴. The outermost shell is the fourth energy level (n=4), and it contains a total of six electrons (two in the 4s orbital and four in the 4p orbital).
Once we know the number of valence electrons is six, we can draw the Lewis dot structure. The standard convention is to place the dots representing the electrons around the chemical symbol of the element. We place one dot on each of the four sides (top, bottom, left, and right) before pairing any of them up. For selenium’s six electrons, this means we would place the first four dots singly on each side, and then the remaining two dots would be added to two of the sides to create pairs.
This process results in a structure with two pairs of electrons, often called lone pairs, and two single, unpaired electrons. The unpaired electrons indicate the typical number of covalent bonds the atom can form.
Let’s examine the options provided:
- Option a: This shows an incorrect and non-standard arrangement of dots.
- Option b: This structure shows the symbol ‘Se’ with two pairs of dots and two single dots. This totals six valence electrons and correctly follows the convention for placing them, representing two lone pairs and two unpaired electrons.
- Options c and d: These structures also show six total dots, but they are arranged into three pairs, with no unpaired electrons. This is an incorrect representation because it doesn’t follow the standard placement rule and inaccurately suggests selenium has no electrons available for bonding.
Therefore, option b is the correct Lewis dot structure for a neutral selenium atom as it accurately depicts its six valence electrons.
