Question

Write formulas for the following ions or compounds: (a) zinchexachloroplatinate(IV) (b) dichlorobis(ethylenediamine)nickel(II) (c) diamminetriaquahydroxochromium(III) nitrate (d) ammonium pentachlorohydroxoferrate(III)

Short answer

In conclusion, we have the following chemical formulas for the given compounds: (a) Zn[PtCl6] (b) [Ni(en)2Cl2] (c) [Cr(NH3)2(H2O)3(OH)](NO3)2 (d) (NH4)3[FeCl5(OH)]

Step-by-step solution

(a) zinchexachloroplatinate(IV)

First, let's break down the name into its components: zinc, hexachloroplatinate(IV). Hexa indicates six, and chloroplatinate(IV) specifies that the compound contains a platinum ion with a +4 oxidation state and six chloride ions. The ion has an overall charge of -2, as the sum of platinum (+4) and six chloride ions (-6) is -2. We also have a zinc atom, which has a +2 charge. In order to balance the charges, we need one zinc ion (Zn) and one hexachloroplatinate(IV) ion (PtCl6). The formula for zinchexachloroplatinate(IV) is Zn[PtCl6].

(b) dichlorobis(ethylenediamine)nickel(II)

Here we have components: nickel(II), two ethylenediamine molecules, and two chloride ions. Nickel(II) indicates a nickel ion with a +2 oxidation state. Ethylenediamine is a neutral ligand (en), and dichlorobis means there are two chloride ions in the compound. The formula for dichlorobis(ethylenediamine)nickel(II) is [Ni(en)2Cl2].

(c) diamminetriaquahydroxochromium(III) nitrate

For this compound, we have the following components: chromium(III), two ammonia molecules, three water molecules, and one hydroxo group. Chromium(III) indicates a chromium ion with a +3 oxidation state. Ammonia (NH3) and water (H2O) are neutral ligands, and hydroxo is a ligand with a -1 charge (OH-). We also have a nitrate ion (NO3-) outside the coordination sphere. The formula for diamminetriaquahydroxochromium(III) nitrate is [Cr(NH3)2(H2O)3(OH)](NO3)2. There are two nitrate ions to balance the +3 charge of the complex ion.

(d) ammonium pentachlorohydroxoferrate(III)

The given components for this compound are: ammonium, iron(III), five chloride ions, and one hydroxo group. Iron(III) indicates an iron ion with a +3 oxidation state. We have five chloride ions (-1 charge each) and one hydroxo group (-1 charge). Ammonium ion (NH4+) is a cation with a +1 charge. The formula for ammonium pentachlorohydroxoferrate(III) is (NH4)3[FeCl5(OH)], with three ammonium ions to balance the -3 charge of the complex ion.

Key concepts

Coordination Compounds

Coordination compounds consist of a central metal atom or ion surrounded by molecules or anions, called ligands. These ligands are usually bonded to the central atom by coordinate covalent bonds, where both electrons in the bond come from the ligand. The resulting structure, known as a coordination complex, has a distinctive geometry such as octahedral, square planar, or tetrahedral, depending on the number and arrangement of the ligands.

In our exercise example, the coordination compounds include 'zinchexachloroplatinate(IV)' and 'dichlorobis(ethylenediamine)nickel(II)'. The names of these compounds provide vital information regarding their composition. For instance, the term 'hexa' refers to six ligands attached to the central platinum ion, resulting in an octahedral geometry for the complex.

Oxidation States

The oxidation state, or oxidation number, of an element in a compound gives insights into the electron distribution and overall charge. It is a hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. A Roman numeral typically indicates this number following the metal in coordination compound names.

For example, in 'zinchexachloroplatinate(IV),' the (IV) indicates that the platinum has an oxidation state of +4. The oxidation state is necessary for determining the charge balance within the complex as it helps us predict the number of required counter-ions or charge on the compound, such as zinc ion (Zn⁺₂) in the compound 'zinchexachloroplatinate(IV)' to balance the charges.

Ionic Charges

Ionic charges refer to the electrical charges present on ions, which are atoms or molecules that have gained or lost one or more electrons. Cations have a positive charge, whereas anions have a negative charge. The total charge on a coordination compound must be balanced, meaning the sum of charges of the central ion, ligands, and any counter-ions should equal zero.

Taking the compound 'ammonium pentachlorohydroxoferrate(III)' as an example, the iron(III) ion has a +3 charge, and the chloride and hydroxo ligands contribute a -1 charge each. Ammonium ions (NH₄⁺) serve as counter-ions to balance out the charge of the coordination complex. Understanding ionic charges is crucial for writing correct formulas of coordination compounds.

Ligands

Ligands are ions or molecules that bind to the central metal atom in a coordination compound through coordinate bonds. Ligands can be anionic (e.g., chloride, hydroxo), neutral (e.g., ammonia, water), or cationic, though the latter is less common. They play a significant role in determining the properties and geometry of a coordination complex.

In the compound 'diamminetriaquahydroxochromium(III) nitrate', the ligands present are ammonia (NH₃) and water (H₂O), which are neutral, and a hydroxo (OH^-), which is anionic. These ligands, through their size, charge, and electronic properties, influence the structure and reactivity of the coordination complex.