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Occupancy of tetrahedral holes

Zinc sulfide is an important industrial source of zinc and is also used as a white pigment in paint. Zinc sulfide crystallizes with zinc ions occupying one-half of the tetrahedral holes in a closest-packed array of sulfide ions. What is the formula of zinc sulfide?

Solution

Because there are two tetrahedral holes per anion (sulfide ion) and one-half of these holes are occupied by zinc ions, there must be 1 2 × 2 , or 1, zinc ion per sulfide ion. Thus, the formula is ZnS.

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Lithium selenide can be described as a closest-packed array of selenide ions with lithium ions in all of the tetrahedral holes. What it the formula of lithium selenide?

Answer:

Li 2 Se

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The ratio of octahedral holes to anions in either an HCP or CCP structure is 1:1. Thus, compounds with cations in octahedral holes in a closest-packed array of anions can have a maximum cation:anion ratio of 1:1. In NiO, MnS, NaCl, and KH, for example, all of the octahedral holes are filled. Ratios of less than 1:1 are observed when some of the octahedral holes remain empty.

Stoichiometry of ionic compounds

Sapphire is aluminum oxide. Aluminum oxide crystallizes with aluminum ions in two-thirds of the octahedral holes in a closest-packed array of oxide ions. What is the formula of aluminum oxide?

Solution

Because there is one octahedral hole per anion (oxide ion) and only two-thirds of these holes are occupied, the ratio of aluminum to oxygen must be 2 3 :1, which would give Al 2 / 3 O . The simplest whole number ratio is 2:3, so the formula is Al 2 O 3 .

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The white pigment titanium oxide crystallizes with titanium ions in one-half of the octahedral holes in a closest-packed array of oxide ions. What is the formula of titanium oxide?

Answer:

TiO 2

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In a simple cubic array of anions, there is one cubic hole that can be occupied by a cation for each anion in the array. In CsCl, and in other compounds with the same structure, all of the cubic holes are occupied. Half of the cubic holes are occupied in SrH 2 , UO 2 , SrCl 2 , and CaF 2 .

Different types of ionic compounds often crystallize in the same structure when the relative sizes of their ions and their stoichiometries (the two principal features that determine structure) are similar.

Unit cells of ionic compounds

Many ionic compounds crystallize with cubic unit cells, and we will use these compounds to describe the general features of ionic structures.

When an ionic compound is composed of cations and anions of similar size in a 1:1 ratio, it typically forms a simple cubic structure. Cesium chloride, CsCl, (illustrated in [link] ) is an example of this, with Cs + and Cl having radii of 174 pm and 181 pm, respectively. We can think of this as chloride ions forming a simple cubic unit cell, with a cesium ion in the center; or as cesium ions forming a unit cell with a chloride ion in the center; or as simple cubic unit cells formed by Cs + ions overlapping unit cells formed by Cl ions. Cesium ions and chloride ions touch along the body diagonals of the unit cells. One cesium ion and one chloride ion are present per unit cell, giving the l:l stoichiometry required by the formula for cesium chloride. Note that there is no lattice point in the center of the cell, and CsCl is not a BCC structure because a cesium ion is not identical to a chloride ion.

Questions & Answers

Modern Electronic Theory
Levi Reply
find the volume of oxygen produced from the electrolysis of acidified water of a current of a 2A was passed through the electrolysis of acidified water for 2 hours
Ngwu Reply
A group of atoms that are connected by chemical bounds
Valerie Reply
molecule
NARCOS_
the atoms are found in the shell, it is called atomic bond.
Andrew
what is molecules
Kelly Reply
what atoms
Simon
Moecules are groups of atoms
Adewole
What is collision theory
Isah Reply
hello guys am new here
Andrew Reply
what is the si unit for energy
enow Reply
joules
udoh
what is Charles law
Ogbu
how do mass of solvent be gram or kilogram ?
Yussuf Reply
by converting
Andrew
its a force a gas exerts on the wall of the container
udoh Reply
compressed it is
Andrew
what is gas pressure
Sandra Reply
the pressure is the amount of Gas that is compressed in the container. in other words because of the gas that is compressed in the container there is pressure on it.
Andrew
write the electron configuration for probium
Magano Reply
what is an accuracy
amadi Reply
what is it
Nhagn
accuracy has to do with speed
Emmanuel
accuracy is the movement of an object in a particular direction without any obstructions.
Andrew
what is titration curve
johnson Reply
a titration curve is the separation of a solvent in a curved direction.
Andrew
explain gaslaws
Felix Reply
explain accuracy
amadi
gas law states that the amount of molecule in the container is inversely proportional to the pressure.
Andrew
what is the functional group in this compound:CH3COCH2CH2-O-CH2
Obafemi Reply
this belongs to the Akane family. after going through this, I noticed the structural formula you gave was wrong. The answer to this is C5H10 heptane.
Andrew

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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