13 solids and modern materials ● ● Graphene- new modern solid compound. ● Carbon solid ● Recently discovered ● Thin as thin as one atom sheet ● Very strong (strongest known material) ● Resistant to the heat ● Still trying to ﬁnd applications for it like in computers, plastics and satellites X-ray crystallography- technique used to ﬁnd structure of any solids ● ● If we pass the x-ray light through the crustal it shows bond angles, size of atoms Crystal lattice ● Unit cell- smallest atom, repeating molecules/atom/particle within crystal. ● Diﬀerent types of unit cells ● In cubic= all bond lengths and all bond angles are equal ● Simple cubic: 1/8 of each corner is of atom ● There is one atom present in ● L = 2radius ● Coordination number=6 ● Packing eﬃciency = 52% ● Body-centered cubic ● 1/8 of each corner particle lies in cell ● And there is one atom inside the cube too ● Packing eﬃciency= 68% ● ● ● ● Coordination number = 8 ● L=4r Face-centered cubic ● Inside the particle there are 3 atoms inside ● And 1/8 of each corner so total= 4 atoms pithing ● Packing eﬃciency = 74% ● Coordination number = 12 Coordination number- number of atoms or molecules surrounding it or the atoms that are touching the central atom. Packing eﬃciency- depends on coordination number, percentage of volume unit cells occupy. ● ● Classiﬁcation of Crystalline solids ● Molecular solids- composed of molecules ● some crystals are called polymorphs- having diﬀerent properties ● Ionic solids- composed of ions ● Anions are larger than cations because of the negative charge ● Cesium chloride- body centered cs in the center and Cl Surrounds it ● ● ● CaS NaCl- face centered cubic arrangement= if size diﬀerence increases, then coordination n number Is less ● Zinc blende and CaF2- face centered- most of the crystals are face centered Atomic solids- composed of atoms - covalent bonds ● Non bonding- no bonds seems ● ● ● Metallic atomic solids- held together by metallic bonds Netwrok covalent● Some crystals form covalent bonds- graphite and diamond ● Graphite- sp2 - 1 pi bond ● Diamond- no double bonds sp3 just cyclic ring ● Buckministerfullernes- new form of carbon- looks like a ball with full carbons ● Nanotubes- made up of chemistry— gold ● Silicates- 90% of earth’s crust quartz silica ● Ceramics ● Cement- Portland cement- very strong ● Glass Semiconductors and Band Theory ● Every atom’s orbital is shared by the entire stricture ● Band Theory- stems from MO theory ● Lower or bonding = valence band ● Anti bonding - conduction band ● If there is no energy gap then the electrons can jump to the conduction band ● ● Insulators- too much energy gap Semiconductiors- acts like conductors and non conductors. They have band gap ● Doping- convert semiconductors into something useful ● Convert into good conductors ● We insert another type of atom into the metal ● N type semicondutors- we add atom with excess of electron ● These electrons can jump into the conduction bands ● P-type - positive- so less electrons ● Creates wholes in metals allowing electricity to pass ● 3rd group atom = p type one less atom ● Didoes- p-n junction ● ● Can be used in ampliﬁers Polymers● Synthetic polymers- we can synthesize them through chemistry ● Natural polymers- naturally occurring in living organisms ● Represent the polymer [/Ch2-Ch2]/

Solids and Modern Materials

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