u3: structure and properties of solids Flashcards
physical properties of a solid depend on
- component elements
- attractive forces present (IMFs)
types of solids
- ionic solid
- metallic solid
- molecular solid
- covalent network
ionic solid definition
- metal and nonmetal
- pos nd neg ion attracted w electrostatic forces
metallic solid definition
- two metals
- atoms
molecular solid
- two nonmetals
- atoms or molecules
covalent network
- metalloids (B, Si, Ge, As, Sb, Te, Po)/carbon
- atoms connected by covalent bonds
ionic crystals
- pure ionic compounds in solid form are 3D crystals
- anions nd cations attracted tgthr in crystal lattice
- each anion surrounded by cations nd vice-versa
crystal lattice
- regular repeating pattern of ions or molecules in a crystal
- exists in 3 dimensions
- ionic substance held by strong electrostatic attraction in all directions
- directional bonds
physical properties of ionic compounds
- hard, brittle, crystalline solids
- high melting and boiling pt (high IMFs)
- don’t conduct electricity as solid, only when molten/aqueous
- soluble in water
metallic crystals
- closely packed lattice
- low ionization energies + low energy unfilled orbitals
- valence elecrons become delocalized (shared by all atoms)
- “electron sea model” bc electrons free to move
metallic bonding
- atoms lose valence electrons = cations
- cations attracted to free electrons = glue
ductility and malleability of metals? alloys?
- attrn not between cations, but cations and mobile electrons: so ions can slide past each other w/o breaking bonds = ductile+malleable
- alloys: pure metal mixed w/ diff metals = harder to slide = harder than pure metals
conducting properties of metals
- bc delocalized electrons free to move = good heat nd electricity conductors
wht does metal bond strength depend on?
- number of electrons atoms share: more electrons = more hold
- how far from nucleus sea of electrons is
how can u figure out melting point based on periodic table
going down a group = lower melting point
why are metals shiny?
when electron absorbs light, jumps to excited state. in sea of electrons, its easier to absorb light, so they shine the light back from all wavelengths of visible light
molecular crystals
- covalent bonds = molecule
- intra (covalent) stronger than inter
physical properties of molecular crystals
- soft in solid state
- dont conduct electricity
- more soluble in non-polar solvent than water
- low melting/boiling pts
examples of covalent network solids
- diamonds
- most gemstones
physical properties of covalent network solids
- very hard
- brittle (no bending, but v hard so rarely break)
- very high melting points
- insoluble in water
- nonconductors
allotropes
diff structural forms of an element
allotropes of carbon
- (a) diamond
- (b) graphite
- (d) fullerenes
structure of diamond
- each carbon joined to 4 others in tetrahedral shape = very strong structure
- all intramolecular bonds = high melting/boililng pt and hardness
structure of graphite
- 2 dimensions covalent network
- made of layers: C atoms bonded to 3 others in trigonal planar form
- each layer is strong
- between layers, there r weak Van der Waals forces
does graphite conduct electricity
- yes bc electrons within are free to move from end to end
- 3 e are bound, 1 is free to travel
how is graphite useful
- large distance between sheets + weak IMFs = layers slide over easily (used as lubricant + pencils)
fullerenes
- approx. spherical molecule
- small amnt of delocalized electrons, not enough to strongly conduct energy
- behaves electron deficient = readily accepts molecules
- molecular molecule = can dissolve in some non-polar solvents
- lower melting pt than diamond/graphite
silicon
- forms 4 covalent bonds
- almost similar structure to diamond
silicon dioxide, its structures
- SiO2
- glass, sand, nd quartz r both SiO2 but differ in structure
- quartz: crystalline bc. order
- glass is not crystalline
how is silicon dioxide similar to silicon and diamond
there is an Si with O between all atoms
semiconductors
- made of pure silicon/germanium
- doped w/ other elements to modify electrical properties
- highest energy lvls r full, but w little energy (heat/light) = electron can jump to next level nd begin to travel
why do covalent network crystals not conduct electricity
bc in covalent bonds, electrons and held = not mobile
