Properties of Ionic Compounds. Properties high melting points –strong electrostatic interactions...
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Properties of Ionic Compounds
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Properties
• high melting points– strong electrostatic interactions between
oppositely charged ions
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Properties
• low vapor pressures– do not easily evaporate
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Properties• tend to be hard and brittle
– break easily
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Properties
• some forms conduct electricity
ionic compound form conducts electricitysolid NO
molten (liquid) YES
aqueous solution YES
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Structure of Ionic Compounds• (+/-) ions form crystal lattice
– regular 3-D pattern or array – ions held in fixed positions
(solid state)
• Unit Cell = smallest repetitive unit in lattice
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Properties of Metallic Bonding
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Metal bonding
• Metals: form organized lattice structures similar to ionic cmpds– adjacent atoms in metal lattice are all same – close proximity of atoms allows outer electron
energy levels to overlap
So…
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Na 3s1 Na 3s1
overlapping valence electron orbitals
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electrons in outer valence shell electrons in outer valence shell move freely through overlapping move freely through overlapping shells shells
• rresults: esults: • ““sea of mobile electronssea of mobile electrons””• (+) metal cations form
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sea of electrons:creates the metallic bond:
•electrostatic attraction between (+) metal cations & sea (-) electrons
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Metal Propertiesval e- moving freely from place to place in
sea of mobile electrons allows metals to:● conduct electricity (flow of electrons)● conduct heatalso accounts for metals being:
● malleable ● ductile ● shiney (luster)
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apply force to metal structure: • metal atoms shift away from force & free e- keep metal cations from separating and breaking• shape becomes deformed
Metal
apply force to ionic compound structure: • forces like charges to align (+) to (+) & (-) to (-) resulting in shattering due to repulsion forces
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as # of electrons that can be delocalized ↑ so does: Hardness and Strength
Na has one valence electron that can be delocalized so: - is relatively soft ( can be cut with a butter knife)
Mg has two valence electrons that can be delocalized so:- still can be cut but is much harder than Na
transition metals have varied # of e-'s that can be delocalized- chromium (Cr+6) is very hard and has high strength
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AlloysAlloys
mixturemixture of elements with metallic properties of elements with metallic propertiesmixture can be adjusted to get desired mixture can be adjusted to get desired
propertiespropertiestwo types:two types:
substitutional and interstitial alloy substitutional and interstitial alloy (depends on size of elements – same or different size)(depends on size of elements – same or different size)
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Common alloysbrass: Cu & Znbronze: Cu, Sn & Alpewter: Sn, Pb & Cusolder: Pb & Snrose gold: Cu & Alwhite gold: Au & Ni, Pd or Ptsterling silver: Ag & Custeel: C & Fe
stainless steel: Cr & Ni
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Properties of Covalent (Molecular) Substances
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Properties
• depend on strength of IMF between “particles” or separate units
• covalent substances:– units are molecules
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Intermolecular ForcesIntermolecular Forces• dispersion forcesdispersion forces occur between non-
polar molecules (Van der Waals)
• dipole-dipole forcesdipole-dipole forces occur between polar molecules
• hydrogen bonding forceshydrogen bonding forces occur between molecules with H-F, H-O, or H-N
Remember: IMF determine phase!Remember: IMF determine phase!
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weakest IMF = dispersion forces weakest IMF = dispersion forces - occur between - occur between non-polarnon-polar atoms/molecules atoms/molecules
● monatomic atoms:monatomic atoms:● diatomic elements:diatomic elements:● small symmetric molecules:small symmetric molecules:
● hydrocarbon molecules:hydrocarbon molecules:
Reminder:Reminder:dispersion forces dispersion forces ↑↑ as size molecule ↑ as size molecule ↑
He, Ne, Ar, Kr He, Ne, Ar, Kr OO22, H, H22, N, N22
COCO22, CCl, CCl44, , CFCF44
CHCH44, C, C44 H H1010
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If a covalent molecule doesnIf a covalent molecule doesn’’t meet the t meet the requirements for a non-polar substance requirements for a non-polar substance
than it is polar than it is polar
and and
will have dipole-dipole IMF or H-bonding forces will have dipole-dipole IMF or H-bonding forces
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Properties: Covalent (Molecular) SubstancesProperties: Covalent (Molecular) Substances
• poor conductors: heat & electricity – no charged particles!
• low mp & low bp:– easy to pull molecules apart from each other
• low Hf and Hv:• not much energy needed to change phase
• high VP: – evaporate easily
• majority of solids are soft
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mp, bp, Hmp, bp, Hff and H and Hvv & VP & VP depend on how difficult depend on how difficult it is to separate particles it is to separate particles from each other from each other
weak IMF – easy to separate particles (need less energy) weak IMF – easy to separate particles (need less energy)
strong IMF – difficult to separate particles (need more energy) strong IMF – difficult to separate particles (need more energy)
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Which substance has the strongest IMF?Which substance has the strongest IMF?
The weakest?The weakest?How know which is weakest/strongest?How know which is weakest/strongest?
waterwater
etherether
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NETWORK SOLIDS• carbon and silicon form extensive networks,
similar to a crystal lattice• different physical properties than molecular
compounds: • hard rather than soft (except graphite)
• high mp & bp, high Hf & Hv
• similar physical properties than molecular cmpds:• non-conductors
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NETWORK SOLIDS: Carbon• most covalent substances are molecular• carbon forms 4 bonds with 4 other C atoms
– allows C to build up extensive network– ex: diamond, graphite
• super strong covalent bonds hold atoms together
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Diamond Structure
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Network Solids: Silicon• silicon can also form network solids
– ex: quartz (SiO2 – AKA sand)
• quartz has very complicated crystal structure