Covalent Network Solids • Crystal held together with covalent bonds
Covalent Network Solid Examples • • • • • • •
C(diamond) C(graphite) SiO2 (quartz, sand, glass) SiC Si WC BN
Properties of Metals Metals are good conductors of heat and electricity. They are shiny and lustrous. Metals can be pounded into thin sheets (malleable) and drawn into wires (ductile). Metals do not hold onto their valence electrons very well. They have low electronegativity.
Properties of Ionic Solids • • • •
Brittle High MP & BP Dissolves in H2O Conducts as (l), (aq), (g)
Intermolecular Forces (IMFs) • Each intermolecular force involves + and – attractions. • The list from weakest to strongest is: – London Dispersion Forces – Dipole-dipole interactions – Hydrogen bonding – Ion-Ion Interactions
Ion-Ion Interaction • + ion attracts a – ion (opposites attract) • Lattice energy is a measure of the strength of this interaction • NaCl(s) + energy Na+(g) + Cl-(g)
Dipole-Dipole Interaction • Same idea as ion-ion interaction, but not as strong because the charges are only “partial charges”. • Polar molecules have this kind of IMF.
Hydrogen Bonding • This is a special case of dipole-dipole interaction (about 10x stronger). • H-O, H-F, H-N – Atoms are small and electronegative – Very polar bond leads to stronger IMF
London Dispersion Forces
London Dispersion Forces • Every atom attracts every other atom with this force. (H-bonding & LDF, Dipole & LDF) • +/- attraction again but the polarity is only temporary. • LDF is stronger with a “more polarizable electron cloud”. (use these words in FRQ) – More electrons – Larger atoms or longer molecules
Examples to Recognize • London dispersion forces – non-polar molecules and other molecules, too. • Dipole-dipole interactions – polar molecules. • Hydrogen bonding – polar molecules with – H-O (water, alcohols, oxoacids) – H-N (ammonia, amines) – H-F (HF)