Properties of Ionic Compounds

Properties

• high melting points– strong electrostatic interactions between

oppositely charged ions

Properties

• low vapor pressures– do not easily evaporate

Properties• tend to be hard and brittle

– break easily

Properties

• some forms conduct electricity

ionic compound form conducts electricitysolid NO

molten (liquid) YES

aqueous solution YES

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

Properties of Metallic Bonding

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…

Na 3s1 Na 3s1

overlapping valence electron orbitals

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

sea of electrons:creates the metallic bond:

•electrostatic attraction between (+) metal cations & sea (-) electrons

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)

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

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

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)

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

Properties of Covalent (Molecular) Substances

Properties

• depend on strength of IMF between “particles” or separate units

• covalent substances:– units are molecules

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!

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

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

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

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)

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?

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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

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

Diamond Structure

Network Solids: Silicon• silicon can also form network solids

– ex: quartz (SiO2 – AKA sand)

• quartz has very complicated crystal structure