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metals and polymers

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Introduction

Properties of materials: Metals and Polymers.

When a metal is in its purest form it is made of ions that are held in place by metallic bonds. Covalent and ionic bonding is different to metallic as the outer shells of adjacent atoms overlap. This then lets the outer shell electrons to move about freely through the lattice in the electron cloud.

image00.jpg

diagram of an electon cloud

Metals atoms have to have a positive charged nucleus and also have negative charged electrons outside. The atom will lose its outer electrons when it is in its solid state. The bonding electrons spread thought the lattice and become delocalised this is because the bonding electrons no longer belong to any particular metal atom. Delocalised means that it is not restricted to one part of the lattice.

Metallic bonds are formed when positive metal ions are attracted to the negative charged electrons which lies in the electron cloud. The strength of these metaillic bonds is determined by two main factors these are:

  • The radius of the individual metal atoms the smaller the radius the stronger it is.
  • Also, the number of electrons that each of the atom donates. The more electrons donated then the stronger the bond.

image01.jpg

Metallic Bonding http://hrsbstaff.ednet.ns.ca/dawsonrj/11%20Chem/Chapter%20notes/Chapter%208%20notes_files/image001.jpg

Metals that consist of metal cations and they have a balancing number of free electrons also have unit cell structures. These types of metals are known to be crystalline structures which can also be described as either:

  • Body Centred Cubic (BCC)
  • Hexagonal Close Packed (HPC)
  • Face centred Cubic (FCC)
...read more.

Middle

Properties of metals.
  • Electrical Conductivity
  • High Metal and boiling points
  • Lustre
  • Thermal Conductivity
  • Strength
  • Malleability

Copper

Copper is lightweight and soft metal that has a reddish tint in colour.

image05.png

Copper and its physical properties.

Melting Point: 1084.62°c

Boiling Point: 2562°c

Young’s Modulus: 110-128 GPa

Density: 8.96g cm-³

Mohs Hardness: 3.0

Vickers Hardness: 369 Mpa

Brinell Hardness: 874 Mpa

Heat Capacity: 25ºC

Electrical resistivity: 200ºC

Thermal Conductivity: 300K

Atomic Radius: 135 Pico metres

(Wikipedia)

Melting and Boiling Points:

Copper has a high melting point and boiling point too as the copper ions have been packed in close together they are found in a fcc structure. Similar to aluminium the copper atoms from one layer arrange themselves so that they then become between the atoms of the layer below. This pattern is then repeated to then build the molecular structure.

Thermal and electrical conductivity:

Copper is also a good thermal conductor because kinetic energy is able to be easily transferred from the closely packed delocalised electrons. Copper is also extremely good at conducting electricity. When there is an electrical potential placed across a strip of copper then the electrons move from the negative to the positive area of the copper and then the current can flow.

...read more.

Conclusion

Thermal and electrical conductivity:

Aluminium is known to be a good thermal conductor as the kinetic energy can be easily transferred from one delocalised electron to the next as they are so closely packed. Because aluminium is a metal it is known to be a good conductor of electricity. This is because of the constant presence of delocalised electrons running through the metallic lattice. When an electric potential is placed across a piece of aluminium then the electrons move from a negative to a positive are of the metal therefore making a current flow.

Malleability and Ductility:

Aluminium is malleable and ductile as it is a face centred cubic structure and is negatively charged. It also the metal inos are able to slide over each other when being shaped. When the metal ions move they produced new attractions with new delocalised electrons, which changes the shape of the aluminium.

Strength                

Aluminium is a strong metal but had a low tensile strength compared to other metals when the structure is changed and deformed when stress is applied. This is because the positive ions move and the delocalised electrons move as well maintaining their attraction to the positive ions.

...read more.

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