Chapter 12- Solids Flashcards
Ionic solids
Sets of cations and anions mutually attracted to one another
- very high melting and boiling pts
Ex: NaCl and MgO
Ionic bonds
Metallic solids
Network of highly delocalized electrons -allows metals to conduct electricity - also responsible for most metals being strong but not brittle - malleable and ductile Example: Cu, Fe - metallic bonds
Covalent network solids
Joined by expensive networks of covalent bonds
- tend to be hard and have high melting pts
Ex: diamonds, C and Si
Covalent bonds
Molecular solids
Discrete molecules that link to one another only by VDW forces and hydrogen bonds
- soft and low melting points
- HBr, H2O
Crystalline solids
Atoms arranged in a very regular pattern
Ex: chloride, quartz, and diamond
Amorphous solids
Characterized by distinct lack of order in the arrangement of atoms
- rubber, glass and obsidian
Crystal lattices
Lattice is repeated pattern
Unit cell is why is repeated
Face centered cubic cell
4 atoms total
74% packing efficiency
Body centered cubic cell
2 atoms total
68% packing efficiency
Alloys
Combinations of two or more elements majority of which are metals
Substitutional alloy
2nd element takes the place of metal atom
Interstitial ally
2nd element fills a space in lattice of metal atoms
Polymers
Contain long chains of atoms connected by covalent bonds
- stronger and higher melting points than molecular solids and more flexible
Cubic lattices
-primitive or lattice or at each corner Or - body centered/ corners and center Or - face centered/ corners and faces
Primitive cubic metal
1 atom per unit cell
Coordination number
Number of neighbor atoms
of cations/ # of anions
Bond order of Molecular orbital theory
1/2(bonding MO- antibonding MO)
Why does melting points rise then fall when going across the periodic table?
MO theory explains that the # of valence e rise to full bonding and strength the bonds but once it is full the melting point falls
Semiconductor
Only group IVA (4 valence electrons)
Covalent network solid
Doping
Increases conductivity
Use element with valence electrons to use as doping agent
Fewer valence e - p type
More valence - n type
Polymers
Molecules of high molecular mass made by sequentially bonding repeating units called monomers
Addition polymers
Made by coupling the monomers by converting a pi bond within each monomer to a sigma bond
Condensation polymer
Made by joining subunits through a reaction in which a smaller molecule (often water) is also formed as a by product
Ex: amino acid and nylon
Properties of polymers
Interactions between chains of a polymer lend elements of order to the structure of polymers
Stretching a polymer
Can increase the amount of order and lead to a degree of crystallinity
Cross linking polymers
Chemically bonding chains of polymers can stiffen and strengthen the substance
Vulcanization of rubber leads to stronger substance
