Ionic Compounds

Question 1

What is another name for ionic compounds?

Answer 1

Salts

Question 2

Properties of ionic compounds

Answer 2

(1) high melting point
(2) Hard and brittle
(3) Molten state is conducting, however solid state is not.
(4) Soluble in highly polar solvents, generates a conductor

Question 3

What is the TYPICAL combination in order to make an ionic compound?

Answer 3

A metal and a nonmetal

Question 4

Why do cations get smaller?

Answer 4

Electrons are being stripped away from the valence shell. This results in a larger Zeff, meaning that the electrons are being pulled closer to the nucleus.

Question 5

Why do anions get bigger?

Answer 5

Electrons are being added which decreases the Zeff allowing for electrons to pull away from the nucleus.

Question 6

What do smaller atoms entail?

Answer 6

Shorter and stronger bonds

Question 7

What do smaller atoms entail?

Answer 7

Shorter and stronger bonds

Question 8

What are Fajan’s rules? What do they relate to?

Answer 8

These rules relate to the formation of covalent ionic bonds. The rules are as follow
(1) Large charges
(2) Small cations
(3) Large anions
(4) Cations that laack a noble gas configuration

Question 9

What’s the charge density equation? Give the final units.

Answer 9

[(charge)(1.6010^-19 C)]/[(4/3)pi*r^3]

C/mm^3 is the units

Question 10

How does a 1:1 swap of ions work?

Answer 10

The charges must be identical and the radii are within 20%.

Question 11

How can swapping ions of alternate charges be done?

Answer 11

The radii must be the same and charges must be compensated for.

Question 12

What are the characteristics of perovskites?

Answer 12

Of the type ABO3 where A is large and 2+ and B is small and 4+. They can be thought of as an octahedral in a cubic cage.

Question 13

What are the characteristics of spinels?

Answer 13

They have a cubic lattice that alternates between Tetrahedral (Td) and Octahedral (Oh) sites.

They are also of the type AB2O4 where A2+ and B3+.

Question 14

Intrinsic Defects

Answer 14

Intrinsic involve vacancies or displacements, but do not change the overall composition.

Question 15

Extrinsic Defects

Answer 15

Involves dopants/impuritites

Question 16

What type of defect is a Schottky defect? Explain what it is.

Answer 16

It is an intrinsic defect that is when there both a loss of a cation and an anion resulting in no change in charge.

Question 17

What is the common system that a Schottky defect would be in?

Answer 17

Its most common in 1:1 systems due to maintaining charge balance.

Question 18

What type of defect is a Frenkel defect? Explain what it is.

Answer 18

It is an intrinsic defect where one of the ions end up in a different site, typically a cation due to their smaller size.

Question 19

In nonstoichiometric compounds how do extrinsic defects effect them?

Answer 19

Involves alternate ionic states of an element getting involved and generates vacancies. Ionic size differences can also cause a variance in the structure.

Question 20

How does doping work as an extrinsic defect?

Answer 20

It introduces other ions to produce changes in reactivity and produces local changes to structure.