!Exam%#%2%Study%Guide%Lectures%10620%Lecture 10 (1/28) and associated readings • Metals o Periods 1 & 2: pre-transition metals, only have s-valence electrons o Al, Ga, In, Sn, TI, Pb, Bi, Po: post transition metals, s and p valence electrons o Sc to Hg: transition metals, (d-block) s and p and d valence electrons o Ce to Lr: f transition metals • D-block o all metals o most are harder, more denser, and possess higher melting points and boiling points than the pre- and post- transition metals o exist in a variety of oxidation states o compounds are usually coloured and often paramagnetic (attracted by a magnetic field) o form coordination compounds • Valence Electrons for D-block metals o abbreviations for how many valence electrons there are; § Sc 4s23d1 § Ti 4s13d2 § Zn 4s23d10 o in the first half of the d-block, the d and s valence electrons are available for bonding o in the second half, fewer and fewer become available o if you form a +2 oxidation state, the first two electrons to go are always s valence electrons o d electrons act as valence electrons in the first half of the d-block, and then act more as core electrons (can’t be lost as easily in the second half elements; results in lower and lower oxidation states From the reading: EFFECTIVE NUCLEAR CHARGE • atomic properties depend on electron configuration and on how strongly the outer electrons are attracted to the nucleus o nucleus – electron attractions are influenced by the magnitude of nuclear charge and the average distance between the two o more complicated in molecules other than H because there are also electron – electron repulsions (in the cloud) in addition to the nucleus – electron attraction § each electron is “screened” from the nucleus by other electrons § Zeff = Z – S where Z is the actual nuclear charge and S is the screening constant; value of S is usually close to number of core electrons in the atom • Take Na: Z = 11+ and since its electron configuration is 1s22s22p63s1, it has 10 core electrons and 1 valence electron floating around § screening is done by the core electrons; any screening by valence electrons is irrelevant • Trends in valence-electron Zeff values o Zeff increases from left to right across a period: number of core electrons stays the same but number of protons increases !!!!!CHEM!1312H!!1nd!Edition!! !o Zeff going down a column changes far less than it does going across a period; it will increase slightly because the more spread out core electron cloud can’t screen the valence electrons as much from the nuclear charge 23.1 THE TRANSITION METALS Minerals: metallic elements that are found in nature as solid inorganic compounds • most transition metals have oxidation states ranging from 1+ to 4+ (to extract a transition metal from a mineral, the oxidation state must be reduced to 0) Properties • increasing Zeff favors a decreasing radius as we move across a period • keep in mind that metallic bonding strength increases, then decreases (halfway through the period) once you hit antibonding orbitals • lanthanide contraction: the filling of 4f orbitals through the lanthanide elements that 1) causes an increase in Zeff and then 2) produces a size decrease Electron Configurations and Oxidation States • when transition metals are oxidized, they lose their outer s electrons before the lose their d subshell electrons o Fe [Ar]3d64s2 vs. Fe2+ [Ar]3d6 vs. Fe3+ [Ar]3d5 o most transition metals have partially filled d subshells, which accounts for these properties: § transition metals often have more than one stable oxidation state § many transition-metal compounds are coloured § often exhibit magnetic properties Magnetism The spin an electron possess gives the electron a magnetic moment aka a property that causes it to behave like a tiny magnet Diamagnetic solid: a solid in which all the electrons are paired (spin-up and spin-down electrons cancel each other out); non-magnetic, actually a little repellant Paramagnetic solid: substance in which atoms or ions have one or more unpaired electrons • electrons in one atom/ion don’t influence the unpaired electrons from neighboring atoms/ions. o as a result, magnetic moments on atoms/ions are randomly oriented and constantly changing direction • when placed in a magnetic field, spins do align; produces a net attractive interaction with the magnet o aka paramagnetic substances will be attracted a little bit to a magnetic field Ferromagnetism: arises when unpaired electrons of an atom/ion are influenced by the orientations of the electrons in neighboring atoms/ions • most stable (low energy) arrangement = electron spins in adjacent atoms/ions are all in the same direction • when a ferromagnetic solid is placed in a magnetic field, electrons align parallel with the field; results in attractive forces one million times stronger than paramagnetism Antiferrogmagnetism: unpaired electrons on a given atom/ion align so that their spins are in the opposite direction with neighboring columns of atoms. • spin up and spin down cancel each other out Ferrimagnetism: substance exhibits both ferromagnetic and antiferromagnetic characteristics • unpaired electrons align so that the spins are in opposite directions • however, the net magnetic moments of the spin ups are not fully canceled by the spin downs; leads to ferrimagnetic materials being similar to ferromagnetic materials - ferro and ferri (Curie temperature, TC), and antiferro (Néel temperature, TN) all become paramagnetic when heated above a critical temperature; thermal energy is sufficient to overcome what determines the spin directions of the electrons! ! 23.2 TRANSITION METAL COMPLEXES Metal complexes: assemblies of a central transition metal ion bonded to a group of surrounded molecules or ion; for ex, [Ag(NH3)2]+ or [Fe(H2O)6]3+ • called a complex ion if it carries a net charge • compounds that contain complexes are known as coordination compounds Ligands: the molecules or ions that bond to the metal ion in a complex • in above example, NH3s and H2Os are the ligands • each ligand functions as a Lewis base and donates a pair of electrons to form the ligand-metal bond; every ligand has at least one unshared pair of valence electrons • typically they are either polar molecules or anions Werner Theory • any metal ion exhibits a primary valence