What’s coming up??? Oct 25The atmosphere, part 1Ch. 8 Oct 27Midterm … No lecture Oct 29The atmosphere, part 2Ch. 8 Nov 1Light, blackbodies, BohrCh. 9 Nov 3,5Postulates of QM, p-in-a-boxCh. 9 Nov 8,10Hydrogen and multi – e atoms Ch. 9 Nov 12Multi-electron atomsCh.9,10 Nov 15Periodic propertiesCh. 10 Nov 17Periodic propertiesCh. 10 Nov 19,22Valence-bond; Lewis structuresCh. 11 Nov 24Hybrid orbitals; VSEPRCh. 11, 12 Nov 26VSEPRCh. 12 Nov 29MO theoryCh. 12 Dec 1MO theoryCh. 12 Dec 2Review for exam

SCREENING AND PENETRATION PENETRATIONIs to get close to the nucleus SCREENINGIs to block the view of other electrons of the nucleus LOOK AT RADIAL PROBABILITY DISTRIBUTIONS

In a multi-electron atomZ eff (s) > Z eff (p) > Z eff (d) E 4s < E 3d ENERGY LEVELS REVERSE!! S-orbital penetrates closer to nucleus

Closer proximity to nucleus  Higher effective nuclear charge, Z eff

1s1s E 2s2s 2p2p 3s3s 3p3p 3d3d 4s4s 4p4p 5s5s 4d4d The result is that 4s lies below 3d

Atoms, molecules or ions with all electrons paired are diamagnetic. Diamagnetic materials are weakly repelled by magnetic fields MAGNETIC PROPERTIES Example: 1s2s2p1s2s2p Ne1s 2 2s 2 2p 6 NEON ALL ELECTRONS PAIRED

Spin quantum number Electrons are influenced by a magnetic field as though they were spinning charges. They are not really, but we think of them as having “spin up” or “spin down” levels.

Atoms, molecules or ions with at least one unpaired electron are paramagnetic. Paramagnetic materials are strongly attracted to magnetic fields. MAGNETIC PROPERTIES 1s2s2p1s2s2p N1s22s22p3N1s22s22p3 Nitrogen atom is PARAMAGNETIC

Which of these is paramagnetic? –NaCa –K + O 2 

PERIODIC TRENDS We will look at some trends in experimentally determined properties such as: IONIZATION ENERGIES ELECTRON AFFINITIES ATOMIC RADII IONIC RADII

TRENDS IN ATOMIC RADII FOR GROUPS 1,2 and 13 to 18 Orbitals bigger as n increases Radial probability density extends further. ATOMIC RADIUS Atomic radii increase down the group

TRENDS IN ATOMIC RADII FOR GROUPS 1,2 and 13 to 18 ATOMIC RADIUS Atomic radii decrease across a period

SCREENING AND PENETRATION ATOMIC RADIUS DECREASES ACROSS PERIOD! WHY?AS WE ADD ELECTRONS The electrons go into same shell and do not screen the nucleus from each other As nuclear charge goes up, so does Z eff Therefore radial probability pulled in….

Z eff increases.. no screening.. radius decreases

Z eff INCREASES RADIUS DECREASES DOWN GROUP...

Z eff DECREASES RADIUS INCREASES

FOR GROUPS 1,2 and 13 to 18 TRENDS IN IONIC RADII Same reasons as for atomic radii……. Cations and anions…... IONIC RADIUS

Cations are smaller than their corresponding neutral atoms. Anions are larger than their corresponding neutral atoms. Na is 186 pm and Na + is 95 pm F is 64 pm and F - is 133 pm same nuclear charge and repulsion among electrons increases radius One less electron electrons pulled in by nuclear charge O < O – < O 2– QUESTIONS…...

ISOELECTRONIC SPECIES? EXAMPLES Which is bigger? Na or Rb Rb …. higher n, bigger orbitals K or Ca K …. poorer screening for Ca Ca or Ca 2+ Ca …. bigger than cation Br or Br - Br …. smaller than anion What about

QUESTION The species F -, Na +,Mg 2+ have relative sizes in which order? 1F - < Na + <Mg 2+ 2F - > Na + >Mg 2+ 3Na + >Mg 2+ > F - 4Na + =Mg 2+ = F - 5 Mg 2+ > Na + >F - ALL 1s 2 2s 2 2p 6 ALL are isoelectronic

QUESTION The species F -, Na +,Mg 2+ have relative sizes in which order ? 1F - < Na + <Mg 2+ 2F - > Na + >Mg 2+ 3Na + >Mg 2+ > F - 4Na + =Mg 2+ = F - 5 Mg 2+ > Na + >F - Check numbers Na + is 95 pm Mg 2+ is 66 pm F - is 133 pm

ELECTRON AFFINITY the energy change associated with the addition of an electron to a gaseous atom. X + e –  X – In general no clear cut trends……. F(g) + e –  F – (g)  E= -328 kJmol -1 EA =  E the electron affinity is negative if  E<0. TWO DEFINITIONS! the electron affinity is positive if  E<0. EA = -  E

TRENDS IN EA ELECTRON AFFINITY MORE NEGATIVE ELECTRON AFFINITY MORE NEGATIVE ELECTRON AFFINITY MORE NEGATIVE

ELECTRON AFFINITIES What is special about … He, Ne and Ar? Be, N and Mg?

He, Ne, Ar: rare gases … adding electron to filled shell … must increase n Be, Mg: alkali earths … adding electron to filled sub-shell … must increase l N: Hund’s rule stability… adding electron to ½-filled degenerate p-shell Q: what would you predict for… Cr, Fe?

TRENDS IN IONIZATION ENERGIES The ionization energy of gaseous atoms M(g)  M + (g) + e - of the elements have been measured…. And we find…….

TRENDS IN FIRST IE Electrons closer to nucleus more tightly held Z eff DECREASES Z eff INCREASES UP THE GROUP IONIZATION ENERGY First Ionization energies decrease down the group

TRENDS IN FIRST IE Greater effective nuclear charge across period Poor shielding by electrons added Z eff INCREASES IONIZATION ENERGY

TRENDS IN FIRST IE

The noble gases have the highest ionization energy! Closed shells most stable