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o ge a alp lP c6 i td I L u d y o s slwsa w iua Lrud nt 1n74 NV fitr 1ys1 tt rn0 Llpt U ud t sWlP Lecture 10 CHEM 1312H 1st Edition 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 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 N el 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 and a secondary valence primary valence the oxidation state of a metal secondary valence number of atoms bonded to the metal ion also called coordination number explains different colours Metal Ligand Bond bond between a ligand and metal is a Lewis acid base interaction o ligands have available electron pairs Lewis …