2Ground State Electron Configurations of the Elements ns2np6Ground State Electron Configurations of the Elementsns1ns2np1ns2np2ns2np3ns2np4ns2np5ns2d10d1d54f5f8.2
3Electron Configurations of Cations and Anions Of Representative ElementsNa [Ne]3s1Na+ [Ne]Atoms lose electrons so that cation has a noble-gas outer electron configuration.Ca [Ar]4s2Ca2+ [Ar]Al [Ne]3s23p1Al3+ [Ne]H 1s1H- 1s2 or [He]Atoms gain electrons so that anion has a noble-gas outer electron configuration.F 1s22s22p5F- 1s22s22p6 or [Ne]O 1s22s22p4O2- 1s22s22p6 or [Ne]N 1s22s22p3N3- 1s22s22p6 or [Ne]8.2
4Cations and Anions Of Representative Elements +1+2+3-3-2-18.2
5Na+, Al3+, F-, O2-, and N3- are all isoelectronic with Ne Na+: [Ne]Al3+: [Ne]F-: 1s22s22p6 or [Ne]O2-: 1s22s22p6 or [Ne]N3-: 1s22s22p6 or [Ne]Na+, Al3+, F-, O2-, and N3- are all isoelectronic with NeWhat neutral atom is isoelectronic with H- ?H-: 1s2same electron configuration as He8.2
6Electron Configurations of Cations of Transition Metals When a cation is formed from an atom of a transition metal, electrons are always removed first from the ns orbital and then from the (n – 1)d orbitals.Fe: [Ar]4s23d6Mn: [Ar]4s23d5Fe2+: [Ar]4s03d6 or [Ar]3d6Mn2+: [Ar]4s03d5 or [Ar]3d5Fe3+: [Ar]4s03d5 or [Ar]3d58.2
70 < s < Z (s = shielding constant) Effective nuclear charge (Zeff) is the “positive charge” felt by an electron.Zeff = Z - s0 < s < Z (s = shielding constant)Zeff Z – number of inner or core electronsZeffCoreZRadius (pm)NaMgAlSi111213141012341861601431328.3
13Cation is always smaller than atom from which it is formed. Anion is always larger than atom from which it is formed.8.3
14The Radii (in pm) of Ions of Familiar Elements 8.3
15I1 first ionization energy Ionization energy is the minimum energy (kJ/mol) required to remove an electron from a gaseous atom in its ground state.I1 + X (g) X+(g) + e-I1 first ionization energyI2 + X+(g) X2+(g) + e-I2 second ionization energyI3 + X2+(g) X3+(g) + e-I3 third ionization energyI1 < I2 < I38.4
17Variation of the First Ionization Energy with Atomic Number Filled n=1 shellFilled n=2 shellFilled n=3 shellFilled n=4 shellFilled n=5 shell8.4
18General Trend in First Ionization Energies Increasing First Ionization EnergyIncreasing First Ionization Energy8.4
19Ionization Energy Trends DOWN a Group Ionization Energy decreases as you move down a group because the electrons that are being lost are in successively higher energy levels – further from the nucleus – requiring less energy to remove them.(Note – although the nuclear charge is greater (more protons), there is more shielding because of the additional electrons… so the overall effective nuclear charge doesn’t really change)
20Ionization Energy Trends DOWN a Group Which has a higher ionization energy, Na or Rb? Explain why.Which has a higher ionization energy, Br or Cl? Explain why.
21Ionization Energy Trends ACROSS a Period Ionization Energy increases as you move across a period because there is an increase in the charge on the nucleus, which increases the effective nuclear charge – requiring more energy to remove electrons from the same energy level.Note: The increase is not totally smooth. Between group 2 and 13 there is a ‘dip’ (decrease) in ionization energy because the electron removed from the element in group 13 is in a p-subshell which is slightly higher in energy than the s-subshells of group 2 and 1. This electron is slightly higher in energy already, so it takes less energy to remove it than it does to remove an electron from the s-subshell.A similar glitch occurs between groups 15 and 16. In group 15 the element has only 1 electron in each p-subshell. In group 16, one of the p-subshells has a pair of electrons. The resulting greater electron-electron repulsion counteracts the effect of the increased nuclear charge... which lowers the activation energy.
22Ionization Energy Trends ACROSS a Period Which has a lower ionization energy, Na or Cl? Explain why.Which has a higher ionization energy, B or Be? Explain why.Which has a higher ionization energy, O or N? Explain why.
23Electronegativity Trends – Why? Down a Group – EN decreasesValence electrons further from nucleusEffective nuclear charge isn’t changingAtom’s ability to attract an electron further away from the nucleus is diminishingAcross a Period – EN increasesCharge on nucleus increases (more protons)Electrons in valence shell are more attracted to nucleus – closerAtom’s ability to attract an electron is increased due to closer distance to nucleus and increase effective nuclear charge.
24Electronegativity Trends – Why? Which has a higher electronegativity, Na or Rb? Explain why.Which has a higher electronegativity, Br or Cl? Explain why.
25Melting Point Trends – Why? Down a Metal Group – MPt decreases slightlyValence electrons further from nucleusEffective nuclear charge isn’t changingAtom’s ability to attract an electron further away from the nucleus is diminishingAcross a Period – MPt increases… then decreases (MPt reflects strength of forces between particles in solid vs liquid states.Gps 1&2 - Strength of metallic bond increases with inc nuclear charge, inc # mobile valence electrons, atomic radius decreasesGps 14 – giant covalent structures… v. strong covalent bonding in all directionsGps – molecular structures… nonpolar… only weak van der Waals forces… mpt depends on mass and size of moleculesGp 18 – single atoms, v wk vdWaals… very low mpt
26Melting Point Trends – Why? Which has a higher melting point, Na or Rb? Explain why.Which has a higher melting point, Na or Cl2? Explain why.Which has a higher melting point, C or O2? Explain why.