Lecture 2511/02/05 Harvard Professor Dimitar Sasselov talk about discovering new extra-solar planets Today 5:30 Refreshments at 5:00 TSB 00 6

Ion Configurations Ions: Anions: negatively charged ions --- gain electrons Cations: positively charged ions --- lose electrons Electrons are gained or lost from subshell of highest n P: [Ne] 3s 2 3p 3  P 3+ : [Ne] 3s 2 3p 0

Ion Configurations For transition metals, remove highest ns electrons first and then (n - 1) electrons. Fe: [ Ar] 4s 2 3d 6  Fe 2+ : [Ar] 4s 0 3d 6  Fe 3+ : [Ar] 4s 0 3d 5

Diamagnetic: Not attracted to a magnetic field All the electrons are paired Paramagnetic: Attracted to a magnetic field Has unpaired electrons

ParamagneticFerromagnetic

Z* is the effective nuclear charge experienced by the outermost electrons. Based on 2 things Positive charge in nucleus Screening from inner shell electrons Explains why E(2s) < E(2p) Z* increases across a period owing to incomplete shielding by inner electrons. Estimate Z* by --> [ Z - (no. inner electrons) ] Charge felt by 2s e- in Li Z* = = 1 Be Z* = = 2 B Z* = = 3 Effective Nuclear Charge, Z*

Give the electron configurations for Cu, Cu +, Cu +2. Are any of these paramagnetic?

Isoelectronic (same electron configuration) Ne: 1s 2 2s 2 2p 6 F:1s 2 2s 2 2p 5 F - :1s 2 2s 2 2p 6 Na:1s 2 2s 2 2p 6 3s 1 Na + :1s 2 2s 2 2p 6

Which of the following species are isolectronic with Ar? Na + K K + Cl -

Atomic Size Can measure atomic radii by experimentally measuring distance between atomic centers C radius: 77 pm Cl radius: 99 pm

Size determined by: Electron shell Higher n  larger size Effective nuclear charge Higher Z *  smaller size

Trends in Ion Sizes

Sizes of Transition Elements 3d subshell is inside the 4s subshell. 4s electrons feel a more or less constant Z*. Sizes stay about the same and chemistries are similar!

Ionization Energy Energy required to remove an electron from an atom in the gas phase. Mg (g) kJ ---> Mg + (g) + e- Mg + (g) kJ ---> Mg 2+ (g) + e- Mg 2+ (g) kJ ---> Mg 3+ (g) + e-

Trends in Ionization Energy IE increases across a period because Z* increases. Metals lose electrons more easily than nonmetals.