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?

The octet rule states that atoms tend to combine in such a way that they each have eight electrons in their valence shell, giving them the same electronic configuration as a noble gas. This rule applies to most elements in the first and second periods of the periodic table, as achieving a full valence shell provides stability.

There are several factors that cause elements in the third row of the periodic table and beyond to not follow the octet rule. These factors include: a) Availability of d-orbitals: Starting from the third period, elements have access to d-orbitals in addition to their s and p orbitals. These d-orbitals can accommodate more electrons, which allows the central atom to form more than four bonds and thus have more than an octet of electrons around it. b) Higher nuclear charge: Elements in the third period and beyond have a higher number of protons in their nucleus. This leads to a stronger attraction between the nucleus and the valence electrons, allowing the atom to hold more than eight electrons. c) Size of the atom: As we move from the second to the third period, the atomic size increases. This results in a longer bond distance between the central atom and the surrounding ligands, which allows the central atom to accommodate more electrons without significant repulsion. d) Polarizability: Elements in the third period and beyond are more polarizable due to their larger atomic size. This means they have a greater ability to distort their electron cloud and accommodate more electrons.

Some common examples of elements in the third row of the periodic table and beyond that disobey the octet rule include: a) Phosphorus (P): Phosphorus can have up to ten electrons around it, as shown in the compound PCl5 (phosphorus pentachloride), where phosphorus forms five bonds with chlorine atoms. b) Sulfur (S): Sulfur can have up to 12 electrons around it, as seen in the compound SF6 (sulfur hexafluoride), where sulfur forms six bonds with fluorine atoms. To summarize, several factors, including the availability of d-orbitals, higher nuclear charge, larger atomic size, and increased polarizability, contribute to the deviation from the octet rule for elements in the third row of the periodic table and beyond.