The coordination number for Mg2+ ion is usually six. Assuming this holds, determine the anion coordination number in the following compounds: (a) MgS, (b) MgF2, (c) MgO.

Verified step by step guidance

Step 1: Understand the concept of coordination number, which is the number of ions of opposite charge that surround an ion in a crystal lattice.

Step 2: Recognize that the coordination number of Mg2+ is given as six, meaning each Mg2+ ion is surrounded by six anions.

Step 3: For each compound, determine the stoichiometry and the ratio of cations to anions. For example, in MgS, the ratio is 1:1, in MgF2, it is 1:2, and in MgO, it is 1:1.

Step 4: Use the stoichiometry to infer the coordination number of the anions. For instance, in MgF2, each F- must coordinate with three Mg2+ ions to maintain the overall coordination number of six for Mg2+.

Step 5: Apply the same logic to MgS and MgO, considering the stoichiometry and the coordination number of Mg2+ to determine the coordination number of the anions in these compounds.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Coordination Number

The coordination number refers to the number of atoms, ions, or molecules that a central atom can bond with in a complex or crystal structure. In ionic compounds, it indicates how many oppositely charged ions surround a central ion, influencing the compound's stability and geometry.

Ionic Compounds

Ionic compounds are formed through the electrostatic attraction between positively charged cations and negatively charged anions. The arrangement of these ions in a lattice structure is determined by their sizes and charges, which directly affects the coordination numbers of both the cation and anion.

Crystal Lattice Structure

A crystal lattice structure is a three-dimensional arrangement of atoms or ions in a crystalline material. The geometry of this lattice is influenced by the coordination numbers of the ions involved, which dictate how they pack together, ultimately affecting the physical properties of the compound.

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A particular form of cinnabar (HgS) adopts the zinc blende structure. The length of the unit cell edge is 5.852 Å. (b) The mineral tiemannite (HgSe) also forms a solid phase with the zinc blende structure. The length of the unit cell edge in this mineral is 6.085 Å. What accounts for the larger unit cell length in tiemmanite?

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Textbook Question

CuI, CsI, and NaI each adopt a different type of structure. The three different structures to consider are those shown in Figure 12.25 for CsCl, NaCl, and ZnS. a. Use ionic radii, Cs+(𝑟=1.81 Å), Na+(𝑟=1.16 Å), Cu+(𝑟=0.74 Å), and, I−(𝑟=2.06 Å), to predict which compound will crystallize with which structure.

Textbook Question

The coordination number for the Al3+ ion is typically between four and six. Use the anion coordination number to determine the Al3 + coordination number in the following compounds: (a) AlF3 where the fluoride ions are two coordinate.