Types of Solids Ionic solids made of cations and anions held together by attractive forces between the two Metallic solids metal metallic bond holds everything together in solid state Molecular solids compounds held by covalent bonds molecules held together by intermolecular forces o Stronger crystalline Weaker amorphous Covalent networks atoms connected through chain of covalent bonds to every other atom in molecule o Ex diamond Physical Characteristics As interactions get stronger in solid we have much higher melting points o Have to overcome intermolecular forces Ex Water vs NaCl vs cast iron vs diamond melting points diamond covalent bonds NaCl ionic interactions cast iron metal water H bond is weakest o Easy to melt water low melting point o Cast iron and NaCl iron has lower melting point o Diamond extremely high melting point to break covalent bonds Ionic compounds fracture under stress Covalent structure needs a lot more force to cut it Metals malleable don t break they bend and stretch to change shape Forces are not localized change shape and directions of intermolecular forces o Can t do that in covalent or ionic solids held rigid in place o In metal move positions of atoms Molecular solids brittle soft when compared to other solids o Ex ice not soft but softER Molecular Orbital MO Theory Ch 9 Highest occupied molecular orbital the HOMO Lowest occupied molecular orbital the LOMO Energy increases as it goes up in orbitals Makes metallic bonds so much easier to deal with Blending of atomic orbitals to form molecular orbitals Lowest energy state to highest fill MOs in the same way as electron configuration Bonding orbitals vs antibonding orbitals 0 K absolute zero no energy left behind all motion has pretty much stopped except electrons Clicker This theory of metallic bonding is called A Music theory D Band theory B MO theory E Gap theory C Hole theory Unoccupied p orbitals ex lithium beryllium in others will form molecular orbitals that we have to worry about Metals Clicker Could a metal at 0 K absolute zero conduct electricity A Yes B No Fermi all electrons are below Fermi level so they can t move If you put in an electron you add energy Not a right answer to this question How does a hole move in a metal Move an electron nearby into the hole creating a new hole Positively charged hole attracted by negative electron Holes and electrons move in opposite directions Semiconductors and Insulators Band gap between valence band filled levels and conduction band empty levels Positive hole below the Fermi level electron promoted to conduction band o Put energy in to excite electrons up into that band if gap is small enough conduct electricity Insulators large band gaps don t allow electrons into conduction band How computers work binary concept electrode is either on or off conduct electricity or not o Can t do it with metal because there is no band gap to turn it off Extrinsic doped in some quantity of another element o Acceptor level provides constant supply of holes Add element that has less electrons Group 3A Holes from lost electrons P type o Donor Level provides constant supply of electrons Add element that has more electrons Group 5A N type o Both in the gap between Conduction and Valence Bands Clicker Extrinsic semiconductors with an acceptor level are referred to as A n type B h type C a type D p type Lattice Energy Ex NaCl Na cation being attracted to 6 Cl anions nearest neighbors repulsion to some Na anions around it too Decreasing interactions as we keep going out Sum of all of these attractive and repulsive forces lattice energy Reporting number lattice energy is negative put in that amount of energy to break lattice Clicker Rank the following compounds from weakest to strongest lattice energies A sodium chloride B Rubidium chloride C Magnesium oxide D Magnesium sulfide 1 1 1 1 2 2 2 2 788 5 687 3826 3406 BADC the more negative the number the stronger the lattice energy Coulombic in nature attraction increases as we increase the charges shorter the distance the interaction increases C D have to have higher lattice energies Oxide is smaller so D has lower lattice energy than sulfide Na is smaller so A has lower lattice energy than rubidium Look at charges first then look at the sizes of the elements Clicker The Born Haber Cycle is based on A Hess s Law B Boyle s Law D Pauli Exclusion Principle C Charles Law E Aufbau Principle Hess s law stated that the change in energy btwn some initial state and some final state is independent from the pathway used to get from the initial state to the final state o Ex 2 start on 4th floor one use stairs to go to 3rd floor one goes up to 6th down to 1st up to 5th down to 2nd and up to 3rd change of state is still 1 o Where did you start and where did you finish is what is important Born Haber some cation and anion MX that starts as solid change them to some state where there are no more attractive and repulsive forces change them to gas phase o Each of the ions will be independent b c they are so far apart Have to look at series of reactions that you can measure o Heats of formation of metal and ions first ionization energies of vapors Calculate the molar enthalpy of formation of solid sodium iodide Cl g e Cl g 349 kJ mol Na g Na g e 496 kJ mol f Cl g 121 3 kJ mol Na g 107 3 kJ mol NaCl s 411 12 kJ mol NaCl s Na g Cl g 2NaCl s 2Na g Cl2 g Na s Na g Cl g e Cl g Na g Na g e NaCl s Cl g Na g