Solids Flashcards
IONIC CRYSTALS
solids consisting of a 3D arrangement of positive and negative ions (metal & non-metal) in a crystal lattice structure
The arrangement of ions within a crystal lattice can be inferred from their crystal shape. For example: Sodium chloride-each ion is surrounded by six ions of opposite charge.
Properties of Ionic Crystals
Relatively hard but brittle
Held together by the attraction of oppositely charged ions
If struck with a hammer ions become distorted and repel one another causing the crystal to break or shatter
High melting points (due to very strong electrostatic forces of attraction b/w ions)
Ionic bonding is much stronger than all intermolecular forces
For example, calcium phosphate, Ca3(PO4)2 (s), in tooth enamel (ionic bonds) is much harder than ice, H2O(s), (hydrogen bonding).
Ionic crystal properties and water (conductivity)
Soluble in water
Conduct electricity in liquid state but not in solid state
METALLIC CRYSTALS
Metallic Crystals are solids with closely packed atoms held together by electrostatic interactions and free moving electrons
Metallic crystal model and bonding
Electron Sea Model is a theory that states that the electrons in a metallic crystal move freely around the fixed positively charged nuclei
Metallic Bonding is the bond that holds the nuclei and electrons of metals together
Metallic crystals and ionication energy
Metals have a low ionization energy and easily give up electrons
The metallic ions pack together as closely as possible and are held in place because of strong electrostatic forces between the ions and the delocalized electrons
Metallic crystal properties
melting points vary widely
sheen, maleable, electrical conductivity, hardness
MOLECULAR CRYSTALS
solids composed of individual elements or molecules held together by intermolecular forces of attraction
Can be polar or non-polar
E.g. iodine, sulfur, ice, carbon dioxide
Properties of Molecular Crystals
low melting point - intermolecular interactions
little hardness - intermolecular interactions
electrical non-conducter - if comprised of non-polar molecules!*
Note: some polar compounds when they dissolve in water can ionize and thus will be conductive in water, but not as strongly as ionic compounds (this does not apply to ALL polar compounds)
COVALENT NETWORK CRYSTALS
solid in which the atoms form covalent bonds in an interwoven network
E.g. diamond, graphite, silicon carbide (SiC), Silicon dioxide (SiO2)
Properties of Covalent Network Crystals
Very high melting points
Extreme hardness
Insoluble
Not good conductors of
electricity
Diamond vs. Graphite
Diamond
is a huge network of C-C linkages where all four of the carbon bonds are equal in strength and the whole structure is enormously strong
Graphite
is a carbon crystal in which each carbon atom uses only three of its four available valence electrons to bond with adjacent carbons atoms
results in layers of carbon that are not bonded
the unused electrons can move freely through layers, explaining why graphite can conduct electricity, whereas diamond, does not
the layers of carbon in graphite are held together by weak London Dispersion Forces
the layers in graphite can slip over one another easily, and although graphite is strong in two dimensions, it is weak in the third dimension
this makes graphite useful for products such as pencils, golf clubs, and as a lubricant. Diamond on the other hand is used to cut glass, and is considered precious due its hardness
Silicon Dioxide (SiO2 (s))
Glass shares the same chemical formula as quartz but lacks the long-range, regular crystalline structure of quartz.
