Question

Question:Give an example of a molecule or ion having a formula of each of the following types and structures.

(a)${\text{AB}}_{\text{4}}^{\text{-}}$ (tetrahedral)

(b) ${\text{AB}}_{\text{2}}$(linear)
(c) ${\text{AB}}_{\text{6}}^{\text{-}}$(octahedral)
(d) ${\text{AB}}_{\text{3}}^{\text{-}}$pyramidal)

Short answer

1. The most common examples for the given molecule are${\text{[BF4]}}^{\text{-}}$ (tetrafluoroborate) and (tetrahydridoaluminate(III).
2. The most common examples for the given molecule are${\text{CO}}_{\text{2}}$and${\text{CS}}_{\text{2}}$.
3. The most common examples of the given molecule are$\text{Sb}{{\text{F}}_{\text{6}}}^{\text{-}}$and$\text{Pt}{{\text{F}}_{\text{6}}}^{\text{-}}$.
4. The most common examples of the given molecule are$\text{Cl}{{\text{O}}_{\text{3}}}^{\text{-}}$ (chlorate) and$\text{Br}{{\text{O}}_{\text{3}}}^{\text{-}}$ (bromate).

Step-by-step solution

Step 1: AXE method

The equations for various structures are presented in general. The aim is to provide real-life instances of the respective species.

The notation${\text{AB}}_{\text{n}}$(geometry) is similar to the so-called AXE method, in both cases, the central atom is designated with$A$, and the ligands are$B$ and $X$, respectively. The main difference is that the geometry is specified in the textbook without the number of lone pairs$\left(E\right)$ on the center being stated explicitly.

Valence shell

a)

Tetrahedral $\text{A}{{\text{B}}_{\text{4}}}^{\text{-}}$-${\text{- AX}}_{\text{4}}{\text{E}}_{\text{0}}$ . This portion can represent all of the halogen elements' $+7$oxidation states. Perchlorate$\left(\text{Cl}{{\text{O}}_{\text{4}}}^{\text{-}}\right)$, perbromate$\left(\text{Br}{{\text{O}}_{\text{4}}}^{\text{-}}\right)$, and periodate $\left(\text{I}{{\text{O}}_{\text{4}}}^{\text{-}}\right)$. The corresponding complex anions are some of the more interesting species:${\text{[BF4]}}^{\text{-}}$(tetrafluoroborate), (tetrahydridoaluminate(III), found in lithium aluminium hydride, for example). The species' space-filling models are listed below. It's also worth noting that the transition metal complex ${\left[{\text{Zn(OH)}}_{\text{4}}\right]}^{\text{2 -}}$has a structure that's very similar to the core ion but with a $-2$charge.

Molecular geometry

b)

Linear${\text{AB}}_{\text{2}}$-${\text{- AX}}_{\text{2}}{\text{E}}_{\text{0}}$. There aren't many examples that correspond to this section. In this geometry, the carbon atom can make two double bonds, hence${\text{CO}}_{\text{2}}$and${\text{CS}}_{\text{2}}$are valid.

However, neither the ${\text{MgCl}}_{\text{2}}$nor the ${\text{SiO}}_{\text{2}}{\text{,PbO}}_{\text{2}}$structures are molecular; they all resemble covalent crystalline structures to some extent. The species' space-filling models are listed below.

Step 4: Chemical properties

c)

Octahedral${\text{AB}}_{\text{6}}^{\text{-}}$-${\text{AXE}}_{\text{0}}$.

Six ligands with a net negative charge around a center are difficult to make from inorganic oxoacids. More coordinative structures would be interesting in this case $\text{Sb}{{\text{F}}_{\text{6}}}^{\text{-}}$and $\text{Pt}{{\text{F}}_{\text{6}}}^{\text{-}}$, while the octahedral geometry is uninteresting, the chemical properties are crucial.

The former anion was observed when platinum hexafluoride oxidized ambient oxygen gas, resulting in the cation (connected to Nobel laureate G.A. Olah's work as well), and the latter anion was observed when platinum hexafluoride oxidized atmospheric oxygen gas, resulting in the${{\text{O}}_{\text{2}}}^{\text{+}}$cation.

The species' space-filling models are listed below.

Step 5: Halogen element

d)

Pyramidal${\text{AB}}_{\text{3}}^{\text{-}}$-${\text{- AX}}_{\text{3}}{\text{E}}_{\text{1}}$. Finally, this family will depict the various halogen elements in their$+5$oxidation states.

The $\text{Cl}{{\text{O}}_{\text{3}}}^{\text{-}}$(chlorate) and $\text{Br}{{\text{O}}_{\text{3}}}^{\text{-}}$(bromate) anions are two instances of corresponding anions.

The species' space-filling models are listed below.