CHEM C4: Solids

Here’s the topic for today:

  • Lattice structure of crystalline solids
    • Ionic
    • Simple molecular
    • Giant molecular
    • Hydrogen-bonded
    • Metallic
  • Materials as a resource
  • Type of structure & bonding in a substance

Let’s go!


How are solids structured?
Solids have 2 types of structure: CRYSTALLINE or AMORPHOUS.

Crystalline solids have particles arranged in an orderly manner.
Amorphous solids have no fixed particle arrangement.

We will focus on crystalline solids here.


What is a Crystalline solid?
Contains particles arranged in an ORDERLY manner.
This orderly arrangement is known as a LATTICE.

The TYPE of crystalline solid can be classified according to the LATTICE PARTICLE & the LATTICE FORCE.

The types of crystalline solids are:

  • Ionic
  • Simple molecular
    • Carbon Nanoparticles
  • Giant molecular
  • Hydrogen-bonded
  • Metallic

Let’s explore each one:


Ionic Solids
(also called ‘giant ionic structures’)

A Level Covalent bonding in halogen molecules, ionic ...

Lattice particles: Positive & negative ions (cations & anions)
Lattice forces: (Strong) electrostatic attraction between oppositely-charged ions
Structure: Positive & negative ions arranged alternatively in a crystal lattice
Trends in Properties caused by: Strength of electrostatic attraction increases when charge density of ions increase
(ex: MgO has Mg2+ & O2-, & is stronger than NaCl which has Na+ & Cl)
Properties: Hard

  • strong attractive forces keep ions together
  • hard to remove ions from the lattice

Brittle

  • when sufficient force is applied in the direction of the layers, layers of ions can be displaced
  • similarly-charged ions repel each other
  • the layers come apart
  • ionic crystal splits along these cleavage planes
High melting & boiling points

  • attraction acts in all directions
  • attraction is very strong
  • requires high heat energy to overcome
  • MP & BP are higher when charge density is higher
Good electrical conductors when molten or aqueous

  • Ions are released from the lattice
  • Free-moving ions able to conduct electricity

Non-conductors when solid

  • Ions are locked in place in lattice
  • No free-moving ions to conduct charges
Soluble in Polar Solvents

  • Ions form immediate attraction with polar molecules of solvent
  • There is sufficient energy from the attraction to separate oppositely-charged ions from the lattice
  • Ions are separated & are free to move
  • Compound dissolves

Insoluble in Non-Polar Solvents

  • Non-polar compounds of the solvent are held by weak van der Waals’ forces
  • Ions are less attracted to the non-polar solvent
  • Ion-ion attraction is stronger than the ion-solvent attraction
  • Ion lattice is not broken
Examples: NaCl, MgO

Simple Molecular Lattice
Van der Waals forces | Ellesmere Chemistry Wiki | Fandom ...

Lattice particles: Discrete molecules
Lattice forces: (Weak) intermolecular van der Waals’ forces (temporary dipole-dipole attraction)
Structure: Molecules arranged in geometric shapes (such as cubes).

Distance between molecules is much larger than distance between each atom within a molecule, because the intramolecular covalent bonds are much stronger than the intermolecular VDW forces.

Trends in Properties caused by: Strength of van der Waals’ forces increase as molecular size increases
Properties: Soft

  • Weak intermolecular forces can be overcome easily with force
  • Molecules separate easily
Low melting & boiling points

  • Weak intermolecular VDW forces can be overcome easily with low energy
  • MP & BP are higher when molecular size increases
Non-conductor in all states

  • No free ions to carry the current
Soluble in non-polar solvent

  • Van der Waals’ forces between solvent molecules are of similar strength as forces between solid molecules
  • Forces are able to pull covalent compounds apart from the lattice

Insoluble in polar solvent

  • Particles of polar solvent have strong permanent dipole-dipole attractions, which are stronger than the weak van der Waals’ attraction of a simple molecular solid
  • Solvent-solvent attraction is stronger than solvent-solid attraction
  • Molecular lattice is not broken
Examples: Iodine (I2)

Carbon Nanoparticles
Carbon can create MANY different forms of structures (allotropes), which can be different types of solids – one of which are carbon nanoparticles.

Nanoparticles can be regarded as simple molecular solids (due to their lattice particles being discrete molecules, & lattice forces being weak VDW), but these exhibit their own distinct properties due to the structures of the molecules themselves.

Lattice Particles: Discrete molecules consisting of carbon
Lattice Forces: (Weak) van der Waals’ forces

Each discrete molecule has a lattice of atoms in itself. The structure of this lattice is what determines the properties of the solid.

Lattice Particles: Carbon atoms
Lattice Forces: Strong Covalent Bonds

Here we will cover:

  • Graphene
  • Fullerenes
    • Buckminsterfullerene
    • Nanotubes

 Graphene

OpenStax CNX

Structure: A single, hexagonally arranged sheet of carbon atoms

Each carbon atom is covalently bonded with 3 other carbon atoms

A 4th valence electron is not bonded, & exists in a p-orbital perpendicular to the sheet

A single isolated layer of GRAPHITE (see below)

Properties: Flexible

  • Sheet can be distorted

Strong (for its mass)

  • Strong covalent bonds do not break easily with force
Reactive

  • Most reactive form of carbon
  • Unbonded (delocalized) electron is free to react with other chemicals
Good electrical conductor

  • Unbonded electron is free to move & conduct electricity across the sheet

Fullerenes
Hollow spheres/tubes consisting entirely of carbon.
Just like graphene, each carbon atom is bonded with 3 other carbon atoms.

Buckminsterfullerene (C60)

Fullerene - Wikipedia

Structure: Football-shaped

Each carbon atom is covalently bonded with 3 other carbon atoms

Carbon atoms are arranged at the corners of 20 hexagons & 12 pentagons

Properties: Soft

  • Weak intermolecular VDW forces can be overcome easily with force
  • Molecules separate easily
Low sublimation point (600C)

  • Weak intermolecular VDW forces can be overcome with little heat energy
Poor electrical conductor (compared to graphite)

  • Electron delocalization is low
Slightly soluble in organic solvents (carbon disulphide, methylbenzene)

  • Van der Waals’ forces between solvent molecules are of similar strength as forces between solid molecules
  • Forces are able to pull covalent compounds apart from the lattice
Reactive

  • High electron density in certain parts of the molecule

Carbon Nanotubes

IBM carbon nanotube breakthrough could bring faster ...

Structure: A single, hexagonally arranged sheet of carbon atoms which bend to form a cylinder

Each carbon atom is covalently bonded with 3 other carbon atoms

Diameter of tube is very small

Length of tube can be millions of times greater than the diameter

Properties: Strong along axis of cylinder

  • Strong covalent bonds do not break easily with force
  • 100 times stronger than steel (per volume)
High melting point (3500C)

  • Strong covalent bonds require high heat energy to break
Good electrical conductor

  • Unbonded (delocalized) electron is free to move & conduct electricity across the sheet

Giant Molecular Lattice

Lattice particles: Atoms
Lattice forces: Strong covalent bonds
Structure: Network of covalent bonds throughout entire structure
Trends in Properties caused by: Strength of covalent bonds

(See bond strength)

We will cover a few examples of giant molecular solids: allotropes of carbon & silicon (iv) oxide.

Each of these solids has differing properties due to differences in structure, so we’ll go through each solid separately.

Graphite

Laboratoire de Physique et Modélisation des Milieux ...

Lattice particles: Carbon atoms
Lattice forces: (Strong) covalent bonds
Structure: Flat sheets of hexagonally-arranged carbon atoms

Each carbon atom is covalently bonded with 3 other carbon atoms

The carbons’ 4th valence electron is not bonded, & exists in a p-orbital perpendicular to each sheet

Multiple sheets of graphene layered upon each other

The sheets are held together by weak van der Waals’ forces

Properties: Easily Scratched

  • VDW forces between layers is overcome easily with force
  • Layers peel off easily
  • Used in pencils (layers flake off & stick onto paper)
  • Good lubricant
High melting & boiling points

  • Strong covalent bonds require high heat energy to break
Good electrical conductor

  • Unbonded electron is free to move & conduct electricity across the sheet
Insoluble in all solvents

  • Solvent molecules cannot penetrate layers
  • Strong covalent bonds keep each layer together


Diamond

3 - Giant Covalent Molecules. - IGCSE Chemistry

Lattice particles: Carbon atoms
Lattice forces: (Strong) covalent bonds
Structure: 3D covalent network

Each carbon atom is covalently bonded with 4 other carbon atoms

Continuous tetrahedral arrangement

Properties: Very hard

  • Strong covalent bonds in every direction
High melting point

  • Strong covalent bonds require high heat energy to break
Non-conductor of electricity

  • All electrons are bonded to carbon atoms
  • No free electrons to conduct electricity
Insoluble in all solvents

  • Solvent molecules cannot penetrate lattice
  • Strong covalent bonds keep lattice together


Silicon (iv) Oxide (Quartz)

3.1.1 (e) Giant Covalent Lattices - Ellesmere OCR A level ...

Lattice particles: Silicon & oxygen atoms
Lattice forces: (Strong) covalent bonds
Structure: 3D covalent network

Each silicon atom is covalently bonded with 4 oxygen atoms

Each oxygen atom is covalently bonded with 2 silicon atoms

Continuous tetrahedral arrangement

Properties: Very hard

  • Strong covalent bonds in every direction
High melting & boiling points

  • Strong covalent bonds require high heat energy to break
Non-conductor of electricity

  • All electrons are bonded to silicon/oxygen atoms
  • No free electrons to conduct electricity
Insoluble in all solvents

  • Solvent molecules cannot penetrate lattice
  • Strong covalent bonds keep lattice together


What is a Hydrogen-Bonded Lattice?

We have covered hydrogen-bonding in ice here.

7.3: Hydrogen-Bonding and Water - Chemistry LibreTexts

Lattice particles: Discrete molecules

Molecules MUST have:

  • lone pair(s)
  • “exposed” hydrogen atom bonded to a nitrogen/oxygen/fluorine atom

in order to form H-bonds.

Lattice forces: Hydrogen bonds
Structure: Dependent on no. of hydrogen bonds per molecule

For ice (H2O), tetrahedral structure

Trends in Properties caused by: Strength of H-bonding increases as:

  • No. of H-bonds per molecule increases
  • No. of lone pairs per molecule
  • Difference in electronegativity between hydrogen & bonded atom
Examples: Ice (H2O), Ammonia (NH3)

What is a Metallic Lattice?
We have covered metallic bonding here.

Tetrahedron | Structure Bonding Material Type | Chemogenesis

Lattice particles: Positive metal ions (cations)
Lattice forces: (strong) electrostatic bond between cations & delocalized electrons

(metallic bond)

Structure: Positive metal ions packed regularly, surrounded by sea of delocalized electrons
Trends in Properties caused by: Strength of metallic bonds increase when:

  • Charge of metal ion increases
  • Size of atom decreases
  • Proton number of metal increases
Properties: Malleable & Ductile

  • Layers of ions can slide across each other easily with force without separating
  • Sea of delocalised electrons binds ions together
High melting & boiling points

  • Strong metallic bonds require high energy to break
  • MP & BP increases across period
    (proton number & ion charge increases)

 

Good electrical conductor

  • Sea of delocalized electrons allow flow of current
Insoluble in all solvents

  • Strong metallic bonds cannot be broken by solvents
Examples: Sodium, Gold, Zinc

2 thoughts on “CHEM C4: Solids

  1. Amirul Zarfan BIn Amali

    For the strength of metallic bonds, shouldn’t when the size decreases the metallic bond increases as the nucleus is nearer to the sea of electrons and less shielding effect

    Like

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