Question

Explain why \(\mathrm{SCl}_{6}, \mathrm{SBr}_{6}\), and \(\mathrm{SI}_{6}\) cannot be prepared.

Short answer

These compounds are not stable due to steric hindrance with the large halide atoms and sulfur's limited coordination capacity.

Step-by-step solution

Determine the Valence Electrons of Sulfur

Sulfur is in Group 16 of the periodic table, which means it has 6 valence electrons in its outer shell. These electrons can potentially form bonds with other atoms.

Determine Maximum Coordination Number

The coordination number refers to the number of atoms bonded to a central atom. For sulfur, the maximum experimentally observed coordination number is limited by the fact that sulfur only has enough d orbitals to maintain a higher than typical octet coordination number. Sulfur typically does not form compounds with a coordination number larger than six.

Analyze the Size of Halides Involved

The iodine, bromine, and chlorine atoms in \(SCl_6\), \(SBr_6\), and \(SI_6\) are relatively large compared to the size of sulfur. This would make it difficult for six halide atoms to simultaneously bond to a single sulfur atom due to spatial and steric hindrance.

Predict Overcrowding Issues

Attempting to bond six large halide atoms to sulfur would lead to significant steric crowding around the central sulfur atom. This would make such compounds unstable and energetically unfavorable to form.

Key concepts

Valence Electrons

Valence electrons play a crucial role in chemical bonding. They are the electrons found in the outermost shell of an atom and are responsible for forming bonds with other atoms. Sulfur, located in Group 16 of the periodic table, has six valence electrons. These are important because they determine how many and which type of bonds sulfur can form.

Sulfur's valence electrons can pair up with electrons from other atoms to form covalent bonds. For example, in a typical molecule like \( ext{H}_2 ext{S}\), sulfur bonds with two hydrogen atoms using two of its valence electrons, while the remaining four electrons remain as non-bonding pairs or lone pairs.

Understanding sulfur's valence electrons is key to predicting its bonding behavior, influencing how complex molecules are structured.

Coordination Number

The coordination number is a concept referring to the number of atoms directly bonded to a central atom in a molecule. For sulfur, the prevalent coordination number is commonly six, but it rarely exceeds this due to orbital limitations.

In chemical terms, sulfur is known to expand its octet and can use d orbitals to accommodate more than the usual eight electrons. However, practically, sulfur does not typically bind with more than six other atoms because beyond this, the spatial arrangement becomes unstable due to electronics and steric factors.

Compounds exceeding a coordination number of six for sulfur are not generally stable nor observed in typical chemical reactions, especially with large atoms like bromine, iodine, or chlorine.

Steric Hindrance

Steric hindrance is a concept in chemistry that describes the restriction of molecule formations due to the size of atoms involved. In the case of \(SCl_6\), \(SBr_6\), and \(SI_6\), steric hindrance explains why these compounds are not feasible.

The halide atoms' large size restricts how many can surround the sulfur atom. When halides are bulky, they require more space. Thus, attempting to crowd six large halide atoms around a central sulfur atom leads to increased repulsive interaction forces. This overcrowding de-stabilizes the compound, making it unlikely to exist under normal conditions.

Such hindrance is an important factor in molecular geometry and determines what structures are possible or energetically favorable.

Sulfur Atom Chemistry

Sulfur atom chemistry is fascinating due to its versatile bonding capacity. As a non-metal in Group 16, sulfur exhibits diverse oxidation states and a capacity to form various compounds.

Primarily, sulfur forms strong double bonds with oxygen – as seen in sulfur dioxide (\(SO_2\)) and sulfur trioxide (\(SO_3\)). In compounds with halogens, sulfur yet struggles due to steric and spatial limitations, especially with larger halogens like bromine and iodine. These elements, due to their size, pose difficulties in forming stable compounds with sulfur due to steric hindrance.

Sulfur's chemistry also includes its famous allotropes, which involve ring and chain structures of sulfur atoms. Understanding sulfur's interactions and its inability to bind with large atoms such as halogens forms an essential part of recognizing sulfur's position in chemical bonding sciences.