Question

For elements in the third row of the periodic table and beyond, the octet rule is often not obeyed. What factors are usually cited to explain this fact?

Short answer

The violation of the octet rule for elements in the third row and beyond is usually attributed to two main factors: 1. Availability of empty d and/or f orbitals, allowing them to accommodate more than eight electrons in their valence shells, and 2. The larger atomic size and weaker nuclear charge control on the outermost electrons, which increases the flexibility in electron distribution and results in extended electron configurations that do not obey the octet rule.

Step-by-step solution

Recall the Octet Rule

The octet rule is a chemical guideline that states that atoms tend to combine in such a way that they each have eight electrons in their valence shells, resulting in a stable electron configuration similar to that of the noble gases. This rule is widely applicable for main group elements (groups 1 to 18) of the periodic table, primarily the elements in the second row (such as carbon, nitrogen, oxygen, and chlorine).

Understanding Electronic Configurations of Elements

Elements in the third row of the periodic table and beyond have a more extensive array of available orbitals. In addition to the s and p orbitals, which are involved in the first two rows of the periodic table, these more massive elements have access to empty d and/or f orbitals due to their larger size and more complex electronic configuration.

Consider the Size of Orbitals

The atomic size of elements generally increases as we move down the periodic table. This results in an increase of available orbitals, and hence, more available electrons for bonding. As the atomic size increases, the positive charge of the nucleus becomes less effective at controlling the electrons in the outermost shells. This causes the outer electrons to have a lower chance of forming stable octet configurations in the elements in the third row and beyond.

Identify the Factors Explaining the Violation of the Octet Rule

The factors that are usually cited to explain the violation of the octet rule for elements in the third row and beyond include: 1. Availability of empty d and/or f orbitals, which allows these elements to accommodate more than eight electrons in their valence shells. 2. The larger atomic size and weaker nuclear charge control on the outermost electrons, which increases the flexibility in electron distribution and results in extended electron configurations that do not obey the octet rule. In conclusion, elements in the third row of the periodic table and beyond often do not obey the octet rule because of their more complex electronic configurations, availability of additional orbitals, and weaker nuclear control over their outer electrons.