Electron Configurations. Ionization Potentials

The diazene molecule has a planar, bent, ground-state structure which was already predicted from the number of the valence electrons by Walsh [1] and later confirmed by experimental and theoretical studies. Two configurational isomers, frans-NsHs and C/S-N2H2, with C2h and C2V symmetry are possible. MO calculations gave the following electron configurations  

With respect to the three highest occupied orbitals, the electronic structure of both molecules is quite different as shown by the ordering of the orbitals and their approximate chemical description For trans-N2H2 (C/S-N2H2) the 4ag(4ai) and 3bu(3b2) MOs are symmetric (n+) and antisymmetric (n ) combinations of the nitrogen lone pairs. The lau(lbi) orbital is the NN Tu-bonding orbital. The MOs 3ag(3ai) and 2bu(2b2) are symmetric and antisymmetric combinations of the NH a bonds, while 2ag(2ai) describes the NN a bond [2, 3]. 

The following ionization potentials were obtained for trans-N2 2 nd trans-N2D2 from the He I photoelectron spectrum and assigned to molecular orbitals by analyzing the observed vibrational structures and by comparing them with other N=N compounds and theoretical calculations [5, 6]  

The adiabatic ionization potential of 9.589 0.007 eV, determined by photoionization mass spectrometry [7], is in excellent agreement with one obtained by photoelectron spectroscopy (see above). Other values for the first ionization potential obtained from various electron impact experiments range from about 9.6 to 9.9 eV [8 to 14], with the most recent measurements giving 9.8 0.05 [11] and 9.65 0.08eV [8]. A value of 9.62 eV was derived from two Rydberg transitions in the UV absorption spectrum (see p. 54) [15]. 

For C/S-N2H2, only calculated ionization energies are known. Quoted here are the results of a many-body Green s function calculation 9.94(3b2), 13.52(4ai), 14.14(1bi), 18.90(3ai), and 22.67(2b2) eV. The corresponding values calculated for trans-N2 2 s reproduced in the correct order and are within 0.3 eV of the measured values [3]. A similar calculation yielding comparable results was reported earlier [2]. 

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Electronic configurations, ionization potentials, atomic/ionic radii, polarizabilities and stability of oxidation states are important chemical properties, whose knowledge is indispensable in assessing similarity of the heaviest elements to their lighter homologs in the chemical groups. 

The PE spectra of simple diaziridines exhibit two bands at lower ionization potentials these are assumed to arise from removal of an electron from one or other of the lone pair MOs. An E arrangement of the two N-bound hydrogens in 3,3-dimethyldiaziridine (37a) is assumed, since the difference of the ionization potentials (0.51 eV) is much smaller than in the fused diaziridine (42) (1.40 eV) which necessarily has the Z configuration (73HCA1614). 

Z Electronic Configuration Oxidation States Geochemical Properties Ionization Potential (kJ/mol) Melting point (K)... 

The largest atoms in the various periods are the group IA metals. The outermost electron resides in a shell that is outside other completed shells (the noble gas configurations) so it is loosely held (low ionization potential) and relatively far from the nucleus. 

When parameters of the Pariser-Parr-Pople configuration interaction molecular orbital (PPP-CI MO) method were modified so as to reproduce the Aol)s values for l,3-di(5-aryl-l,3,4-oxadiazol-2-yl)benzenes 16 and 17, the calculated HOMO and LUMO energy levels corresponded with the experimental ionization potential and electron affinity values. The relationships between the electrical properties and molecular structures for the dyes were investigated. The absorption maximum wavelengths for amorphous films were found to be nearly equal to those for solution samples <1997PCA2350>. 

Transition metals tend to have higher melting points than representative metals. Because they are metals, transition elements have relatively low ionization energies. Ions of transition metals often are colored in aqueous solution. Because they are metals and thus readily form cations, they have negative standard reduction potentials. Their compounds often have unpaired electrons because of the diversity of -electron configurations, and thus, they often are paramagnetic. Consequently, the correct answers are (c) and (e). 

Element Atomic number Atomic mass Electronic configuration Pauling electronegativity Ionization potential Ionic radius Atomic radius... 

Symbol Ar atomic number 18 atomic weight 39.948 an inert gas element electronic configuration Is22s22p63s23p ionization potential 15.76eV stable isotopes and natural abundance Ar-40 99.6%, Ar-36 0.337%, Ar-38 0.063% unstable isotopes, half-life and disintegration mode ... 

Symbol Ba atomic number 56 atomic weight 137.327 a Group llA (Group 2) alkaline earth element electronic configuration [Xejs valence state +2 ionic radius of Ba2+ in crystal (corresponding to coordination number 8) 1.42 A first ionization potential lO.OOeV stable isotopes and their percent abundances Ba-138 (71.70), Ba-137 (11.23), Ba-136 (7.85), Ba-135 (6.59), Ba-134 (2.42) minor isotopes Ba-130 (0.106) and Ba-132 (0.101) also twenty-two radioisotopes are known. 

Symbol Be atomic number 4 atomic weight 9.012 a Group IIA (Group 2) metal the lightest alkaline-earth metallic element atomic radius l.OOA ionic radius (Be2+) 0.30A electronic configuration Is22s2 ionization potential, Be 9.32eV, Be + 18.21 eV oxidation state +2... 

Symbol Cd atomic number 48 atomic weight 112.41 a Group IIB (Group 12) metallic element ionization potential 8.994eV electron configuration [Kr]4di°5s2 valence state +2 standard electrode potential, E° -0.40V. The isotopes and their natural relative abundance are ... 

Symbol Cs atomic number 55 atomic weight 132.905 a Group lA (Group 1) alkali metal element electron configuration [Xe]6si atomic radius 2.65 A ionic radius (Cs ) 1.84 A ionization potential 3.89 eV valence +1 natural isotope Cs-133 37 artificial isotopes ranging in mass numbers from 112 to 148 and half-lives 17 microseconds (Cs-113) to 2.3x10 years (Cs-135). 

Symbol Kr atomic number 36 atomic weight 83.80 a Group 0 (Group 18) element inert gas element electron configuration Is22s22p63s23p 3di°4s24p valence state 0 an uncommon valence state +2 exists for its difluoride first ionization potential 13.999 volt six stable natural isotopes are known most abundant isotope Kr-84. Natural isotopes and their abundances Kr-78 (0.354%), Kr-80 (2.20%), Kr-82 (11.56%), Kr-83 (11.55%), Kr-84 (56.90%), Kr-86 (17.37%). 

Symbol Mg atomic number 12 atomic weight 24.305 a Group II A (Group 2) alkaline-earth metal atomic radius 1.60A ionic radius (Mg2+) 0.72A atomic volume 14.0 cm /mol electron configuration [Ne]3s2 valence +2 ionization potential 7.646 and 15.035eV for Mg+ and Mg2+, respectively three natural isotopes Mg-24(78.99%), Mg-25(10.00%), Mg-26(11.01%). 

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