Structure and properties of solids

Structure and properties of solids

by Ms. Hypolite

​Lesson objectives

​Students should be able to:

1. ​Identify the four types of solid crystal structures

2. ​Give examples of each type of crystal compounds

3. ​Explain how the structure of sodium chloride relates to its properties

4. ​Compare the properties of ionic solids and simple molecular solids

5. ​Give examples of giant molecular crystals

6. Define allotropy

7. ​Relate the structure of diamond and graphite to their properties and uses

​Types of solid crystals

​Solids can be grouped into the following based other structure:

1. ​Ionic crystals

2. ​Simple molecular crystals

3. ​Giant molecular crystals

4. ​Metallic crystals

Ionic and simple molecular solids ​

​Ionic Crystals

These are made of an ionic lattice with strong ionic bonds

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​They are represented using empirical formulae or formula units

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​Examples include:

• ​Sodium chloride

• ​Sodium fluoride

• ​Ammonium nitrate

• ​Ammonium chloride

​Simple molecular crystals

​ Made of a molecular lattice in which weak forces of attraction (intermolecular forces) hold small molecules together in a regular 3D arrangement.

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​The atoms within each molecule are bonded together by strong covalent bonds (intramolecular force)

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​Simple molecular crystals are represented by molecular formulae.

​Examples of simple molecular crystals

​Question [10 minutes]

Which type of crystal structure does the following have?

• ​Ice

• ​Calcium carbonate

• ​Iodine

• ​Potassium bromide

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​Covalent bonds are very strong. Explain why the melting point of simple molecular solids so low?

Giant molecular crystals​

What is a giant molecular crystal?

​A giant molecular crystal is composed of a giant molecular lattice in which strong covalent bonds hold non-metal atoms in a regular, 3-D arrangement throughout the lattice

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​These crystals are represented by empirical formulae

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​Examples include:

​Diamond

​Graphite

​Silicon dioxide

​Allotropes

​Diamond and graphite are known as allotropes

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​Allotropes are different structural forms of a single element in the same physical state

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• ​They have the same chemical properties

• ​They have different physical properties because they are bonded differently

​Question [10 minutes]

​By referring to their structure, explain EACH of the follwoing

1. ​sodium chloride is soluble in water

2. ​diamond is used in cutting tools

3. ​graphite conducts electricity

4. ​graphite is used as the lead in pencils