Housekeeping Flashcards
Background knowledge
What is metallic bonding?
Metallic bonding is a type of chemical bonding that arises from the electrostatic attractive force between conduction electrons and positively charged metal ions. It may be described as the sharing of free electrons among a structure of positively charged ions.
Outermost (valence) electrons are shared between atoms - “sea of electrons”
Mobile electrons, this makes metallic bonds relatively easy to rearrange, hence metals tend to be ductile.
Typical mechanical properties of metals?
Ductile and malleable
Stiff
Strong
(Other properties, which are less concerning structural engineering; Non-transparent, electrically conducting, high thermal conductivity)
What are most metals?
Often alloys (one or more metallic elements, possibly with small amounts of non-metals)
What is Covalent bonding?
Involves sharing of electrons between adjacent atoms, which results in strong, directional bonds (these are not easy to rearrange,and tend to result in stiff, hard materials, e.g. diamond)
What is Ionic bonding?
Involves complete transfer of electrons between atoms to form positive and negative ions
Positive ions - atoms that have given up 1 or more valence electrons, e.g. metal ions
Negative ions - atoms that have gained 1 or more valence electrons
Example: Common salt (sodium chloride NaCl)
What is a typical mechanical property for ceramics?
Stiff
Hard
Brittle
(other properties; temperature resistant, electrically insulating (not always), low thermal conductivity)
What compound do ceramics tend to be?
Compounds between metals and nonmetals (e.g. oxides, nitrides, carbides)
What bonding do ceramics tend to experience?
Covalent and ionic bonding
(can’t rearrange bonds easily therefore tend to have a brittle manner)
What are the mechanical properties of glasses?
Stiff,
Hard,
Brittle
(other properties; transparent (not always), electrically insulating, low thermal conductivity)
What Structure does a polymer have?
Long-chain organic molecules
C-based chains - can be linear or branched
Thermoplastics - non-cross-linked chains
Thermosets- cross-linked chains
What is attached to the chains also matters - functional groups
What kind of bonding do polymers have?
Strong covalent bonds in molecules and intermolecular bonds may be strong or weak
What are the typical mechanical properties of polymers?
Not stiff (useful for expansion joints etc.), Not strong, ductile, low-density
What are composites?
Combination of different classes of materials (aim to get the benefits of both materials, without any of the disadvantages)
