Metallic Bonding

  • Created by: robw6
  • Created on: 23-04-19 17:27

Metallic Bonding

Metals:

  • High melting and boiling points
  • Outer shell of electrons are free to move
  • Strength = force of attraction between ions and electrons
  • More free electrons = Stronger the metal and more conductive
  • Lots of energy need to be broken down
  • Free electrons allow metals to conduct heat and electricity
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Ionic Bonding

Ionic compounds = Transfer of electrons from a metal to a non metal

  • Ions are formed when electrons are transferred between atoms during chemical bonding
  • Will have a positive or negative charge

e.g When Sodium Chloride (NaCl) forms, one electron is transferred to chlorine. This will form a full stable outer shell for the two particles

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Covalent Bonding

Chemical bonding between two or more non metals.

  • Atoms share electrons
  • Molecules are nuetral (no charge)

When hydrogen gas (H2O) forms, electrons are shared between two atoms to form a molecule.

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Giant Ionic Structures

  • Giant Lattice Structures

Strength of electrostatic force of attraction between oppositely charged ions = High melting and boiling points

  • The ions are arranged in a regular way to form a giant Ionic Lattice

-+-+-+

-+-+-+

  • Lattice = regular
  • Giant = repeated many times with a large number of ions
  • Ions compunds often form crystals

Number of ions in a compund is such that the overall charge of a sample ot the compund is zero

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Simple Molecular Structures

  • Small number of atoms joined my covalent bonds
  • Covalent bondfs are very strong but there are only very weak forces holding the molecules to each other
  • Low temperature required to seperate molecules when they are melted or boiled
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Giant Covalent Structures

  • Lots of non metal atoms each joined to adjacent atoms by covalent bonds
  • Arranged into giant lattices which are strong because many bonds are involved
  • Very high melting points

Diamond:

  • Form of carbon in which each atom is foromed to 4 other carbon atoms
  • Very hard and has melting point of over 35000 C
  • Does not conduct electricity
  • Tranparant/Crystalline
  • Gemstones, Glass cutting, Drill bits

Graphite

  • Form of carbon in which carbon atoms form layers
  • Each carbon atom is joined to 3 others
  • Fourth electron becomes delocalised between the layers
  • Conducts electricity
  • Layers can slide over each other
  • Pencils and lubricant

Silica

  • Similar structure to diamond 
  • Hard and has high melting point
  • Contains silicon and oxygen atoms insteqad of carbon atoms
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Carbon

Can also form:

Fullerenes - cages and tubes with different numbers of carbon atoms

  • Buckminsterfullerene - Molecules are spherical and contain 60 carbon atoms

Fullerenes may be used for drug delivery systems in the body, in lubricants and as catalysts

  • Nanotubes - useful in reinforcing structures where lightness and strength are needed
  • Conduct electricity / used in semi-conductors
  • Small diameter - 10000 times less than human hair
  • Single layer of graphite structures

Graphene is strongest material ever and best electrical conductor

Individual atoms do not have the same properties as bulk materials

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Smart materials

Properties that react to changes in their environment

  • Shape-memory alloys / polymers

Will return to its original shape when heated

  • Colour-cahnge materials

Thermochromic - changes cokour as temperature changes

Photochromic - changes colour according to different lighting conditions or changing light intensity

  • Polymer Gels

Can absorb / expel water and swell / shrink due to cahnges in pH, temperature, salt concentration etc.

  • Electroluminescent Materials

Give out light when an electrical current is passed through them

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Nano-materials

Range in size from 100 nm to 1 nm

Properties that are different from the same substance in bulk

Properties and uses:

  • Very large surface area compared to volume so are able to react verty quickly
  • Useful as catalysts to speed up reactions

Titanium dioxide is a white solid used in house paint and certain chocolates. Titanium dioxide nanoparticles are so small that they do not reflect visible light, so cannot be seen. They are used in sun screen to block harmful ultraviolet light.

Nano-sized silver particles are antibacterial, antiviral and antifungal and are used in plasters, antiseptic sprats etc.

Nanoscience may lead to:

  • New catalysts
  • New coatings
  • New computers
  • Stronger and lighter building materials
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