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 formconducts electricity solid 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 3s 1 overlapping valence electron orbitals

electrons in outer valence shell move freely through overlapping shells results: results: “sea of mobile electrons” “sea of mobile electrons” (+) metal cations form

sea of electrons: creates the metallic bond: electrostatic attraction between (+) metal cations & sea (-) electrons

Metal Properties val e - moving freely from place to place in sea of mobile electrons allows metals to: ● conduct electricity (flow of electrons) ● conduct heat also 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

Alloys mixture of elements with metallic properties mixture of elements with metallic properties mixture can be adjusted to get desired properties mixture can be adjusted to get desired properties two types: two types: substitutional and interstitial alloy substitutional and interstitial alloy (depends on size of elements – same or different size)

Common alloys brass: Cu & Zn bronze: Cu, Sn & Al pewter: Sn, Pb & Cu solder: Pb & Sn rose gold: Cu & Al white gold: Au & Ni, Pd or Pt sterling silver: Ag & Cu steel: 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 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!

weakest IMF = dispersion forces - occur between non-polar atoms/molecules - occur between non-polar atoms/molecules ● monatomic atoms: ● diatomic elements: ● small symmetric molecules: ● hydrocarbon molecules: Reminder: dispersion forces ↑ as size molecule ↑ He, Ne, Ar, Kr O 2, H 2, N 2 CO 2, CCl 4, CF 4 CH 4, C 4 H 10

If a covalent molecule doesn’t meet the requirements for a non-polar substance than it is polar and will have dipole-dipole IMF or H-bonding forces

Properties: Covalent (Molecular) Substances poor conductors: heat & electricity –no charged particles! low mp & low bp: –easy to pull molecules apart from each other low H f and H v : not much energy needed to change phase high VP: –evaporate easily majority of solids are soft

mp, bp, H f and H v & VP depend on how difficult it is to separate particles from each other weak IMF – easy to separate particles (need less energy) strong IMF – difficult to separate particles (need more energy)

Which substance has the strongest IMF? The weakest? How know which is weakest/strongest? water ether

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 H f & H v 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 (SiO 2 – AKA sand) quartz has very complicated crystal structure