AQA C2: Ionic Substances and their Properties

Includes ionic and covalent structures, differences between ionic and covalent bonds, giant metallic structures.

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  • Created by: Jessica
  • Created on: 21-02-12 01:07

Ionic Compounds

Ionic bonds form when a metal reacts with a non-metal. Metals form positive ions and non-metals form negative ions. An ion is simply an atom with a charge.

Opposite charges attract, so ionic compounds are held together with electrostatic forces. They are held together in a lattice structure.

Properties of Ionic Compounds:

High melting point

Ionic compounds have very strong bonds, which require a lot of energy to break.

Conduct electricity when in liquid form or a solution.

Ions are charged particles but can only conduct electricity when they are free to move.

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Simple Covalent Compounds

Covalent bonds form when two or more non-metals react. The particles are held together with shared electrons, which creates a strong bond. 

Examples of Simple Covalent Compounds:

CO2 (one carbon atom and two oxygen atoms)

H2O (two hydrogen atoms and one oxygen atom)

Properties of Simple Covalent Compounds:

Low melting and boiling points

The weak intermolecular forces are broken easily

Non conductive

The atoms are not ions so they have no charge. There are no free electrons either.

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HIGHER TIER

Hydrogen (H2), methane (CH4) and water (H2O) are simple covalent compounds. They have very strong bonds between the atoms, but the intermolecular forces are much weaker. Intermolecular forces hold the molecules (H2O) together in a structure, and the covalent bonds hold the atoms (i.e. H, O and O) together in a molecule. 

When a simple covalent substance melts or boils, the intermolecular forces are easily broken, which is why covalent compounds have low melting/boiling points. 

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Giant Covalent Structures

A giant covalent structure, includes lots of non-metal atoms arranged in a lattice structure. They are held to adjacent atoms with covalent bonds.The lattice structure is extremely strong, because there are many bonds involved. Diamond, silica and graphite are all allotropes of carbon and are arranged in lattice structures. 

Giant Covalent Structures have different properties to Simple Covalent Structures...

Very high melting and boiling points

Because there are so many covalent bonds involved, GCS require a lot of energy to break the bonds. 

Conductivity varies

Diamonds don't conduct electricity, graphite has free electrons so it does conduct electricity, and silica is semi-conductive

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Nanoparticles

A nanometre is a billionth of a metre. Therefore nanoparticles are extremely small - far too small to be seen with a microscope. Nanoparticles can measure 1nm to 100nm.

Properties of nanoparticles:

  • Very large surface area to volume ratio
  • React very quickly
  • Often have different properties than the same substance in a larger form

Uses of nanoparticles:

  • Catalysing reactions
  • In computers
  • Specific uses: e.g. titanium dioxide doesn't reflect light, so it is used to protect skin in a sunblock.



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Metallic Bonding

Metals have free electrons. When they are bonded in giant metallic structures, these electrons are still free to move. Metallic bonds are strong, so metals usually have high melting/boiling points.

Metals are good conductors of heat and electricity, because the free electrons can carry a charge or heat through the metal.

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