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Amorphous Solids
• Amorphous solids: rigid, appear solid but do not behave like crystalline
solids
• Amorphous: without form
• These substances occasionally referred to as supercooled
liquids=more accurate description of their behavior and structure
• Most common amorphous materials: glass, rubber, several plastics
• Cooled to such low temperatures that viscosities become high enough
to prevent liquid flow
=>particles trapped in disordered arrangement
• Heated=gets softer before it melts
• Crystalline solids show no such temp
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14-23
Metallic Solids
• Have small number of valence electrons
• Held together by: attraction between mobile valence E and fixed
positive metal ions
• Principal feature of metallic bond: mobility of valence electrons around
positive metal ions
=>ions remain fixed in their locations in 3-dimensional crystal array
• Good electrical conductors because valence E are free to move
• Good thermal conductors because E can transmit heat energy
• 2 other important properties: malleability, ductility
• ductility: ability to be drawn into wire
change shape=>continues to hold together because E can shift to bond
atoms in new positions
Molecular Solids
• particles can be atoms or molecules
• held together by: intermolecular forces
• substances that consist of molecules: solids at room temp
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NaCl)
• oppositely charged ions: close to each other, similar charge: farther
=>maximizes attractions, minimizes repulsions=greatest stability
• ionic solids tend to be: hard and brittle, high melting points
=>ionic bonds quite strong
• also poor conductors of heat and electricity
=>ionic substance in liquid state (only exists at high temp
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diamond form of C (diamond, graphite=naturally occurring forms of
C)
• different structures of diamond and graphite produce different physical
properties, although they are both forms of the same element C
• diamond: every C atom bonds to 4 other C atoms in giant 3-D network
of covalent bonds
• graphite: C atom covalently bonds to 3 other C atoms in a planar
arrangement; planes/”sheets” are held together by dispersion forces
that are weaker than C-C bonds
• E found between planes are free to move, like valence E in metals
=>graphite: electrical conductor, diamond is not
• “sheets” can also slide past each other easily=used in pencils



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