Types of Solid

8/13/2019 Types of Solid

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Types of Solids


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Intermolecular Forces in Solids

The molecules in solids are heldvery tightly together, restrictingtheir movement.

This means that the intermolecularforces are significant.

We can classify solids based on the

type of intermolecular forcesholding them together.


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Types of Solids

We will classify solids into fourtypes:

1. Molecular Solids2. Metallic Solids

3. Ionic Solids

4. Covalent network solids


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Molecular solids

Consider the element Iodine, I2 Iodine is a solid at room

temperature and pressure

What intermolecular forces maintainthis solid state?

Only London forces!

However, it has 53 electrons, givingit sufficient intermolecular force tobe a solid at room temperature.


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Molecular solids

A molecular solid is a solid thatconsists of atoms or molecules heldtogether by intermolecular forces

Examples include:

Solid neon (melting point of -248oC)

Solid CO2(dry ice)

Solid H2O (ice)

Iodine

Sugar


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Metallic solids

Metals usually have very highmelting points, although this can behighly variable. For example, mercury melts at -39oC while

tungsten melts at 3410oC

Therefore, the intermolecular forces

in metals must be rather strong. These forces are not completely

understood.


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Metallic solids

In metals, the valence electrons ofneighbouring atoms form a sort of

electron soup

These electrons are calleddelocalized electrons

This delocalized electron soup can

be thought of as a glue that holdsthe positive nuclei of the metalatoms together.


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Metal solids can be thought of as being like a ricekrispy square

The marshmallow is like thedelocalized electron soup thatacts a glue that holds it together

The rice krispies are like thepositive nuclei of the metalatoms that compose the solid.


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Metallic solids

The positive nuclei of metals formlattice structures within the electronsoup.

This means that metals arecomposed of crystals, but they areusually too small to see.

However, formation of metalsthrough electroplating can make thecrystalline nature more obvious.


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Ionic Bonding

Ionic compounds have the followingphysical properties:

Very high melting points

Brittle

Non-conductive in a solid state

Conductive in a liquid state


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Ionic Bonding

The forces involved in ioniccompounds are derived from thecreation of a crystal latticecomposed of alternating negativeand positive ions.

Because of the full charge on ions,

ionic bonds are stronger thandipole-dipole interactions


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Different Types of Crystal Lattices


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Arrangement of Ions in a Sodium

chloride cystal (cubic)


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Covalent Network Solid

Consider carbon dioxide (CO2) andsilicon dioxide (SiO2).

What would you expect the physicalproperties of SiO2to be?

CO2b.p. = -78.5oC

If London forces are the only

intermolecular force, then youmight predict the b.p. of SiO2to beslightly more than CO2.


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Covalent Network Solid

However SiO2has a m.p. of 1650oC,

and b.p. of 2230oC!

SiO2is also known as quartz, orsand, is used in the production ofglass.

Clearly, SiO2is not a molecular solid

like CO2is.

SiO2is a covalent network solid.


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Amethyst quartz (SiO2)


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Diamond

Diamond is another allotrope ofcarbon.

Like graphite, it is a covalent

network solid. However, instead of sheets, it forms

a 3-dimensional lattice of carbonatoms.

This is what gives diamond itscharacteristic hardness.


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Types of Solid

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