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Subtleties of the shell structure of the atom

Subtleties of the shell structure of the atom. Physically speaking why does the 4 s level in neutral atoms lie below the 3 d ?. The s orbital has a small fraction of its probability density close to the nucleus .

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Subtleties of the shell structure of the atom

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  1. Subtleties of the shell structure of the atom Physically speaking why does the 4s level in neutral atoms lie below the 3d? The s orbitalhas a small fraction of its probability density close to the nucleus. 3d orbitals do nothave such inner regions, as they only have planar nodes Hence an selectronfrom a highershell will sometimes occur at lower energy than a d electron in a lower shell

  2. Effective nuclear charge The charge that a 2s or 2p electron feels is different due to the shielding from the electrons in the 1s orbital E From Li to Ne, nuclear charge increases from 3 to 10 -1.77 -1.42 -2.78 2 s orbital penetrate into the 1s orbital and therefore are shieldedless on average than p orbitals -3.15 -3.51 -3.87 Note: Shielding effect increases as the numberofe’sincreases. This is the result of additional shielding from the 2 s and 2 p e’s Note: As Z*increasesorbitalsshrink towards nucleus as e’s are held more tightly dues to stronger electronic interactions.

  3. Consider the change in sizeof the atoms from Li to F Effect on atomic size Decrease strongly Consider the size change from Li to Rb • Consider the size change from F to I Increase significantly Consider the size change from F to I Increase gently

  4. Size of Atoms and Ions Atomic radiusdecreasesalong the period, and increases down the group The radius of an anion is larger than its neutral atom. Adding the extra electron increasesshielding without changing the charge of the nucleus. Ie.Z* is smaller. The radius of a cation is smaller than its neutral atom Removing the electron decreases shielding without changing the charge of the nucleus. ie.,Z* is larger. Valence electrons of a cations are in a lower energy shell than in the neutral atom, decreasing the ionic radius.

  5. Sizes of monatomic ions Anions are larger than cations This is always true across a period of the table Ions in each group of the table get larger in size down the group Isolectronicions decrease in size across the period, as Z* increases dramatically. Ex) N3- to F- Na+ to Al3+

  6. Ionization energy The energy that must be absorbed in order to remove a valence electron from a neutral atom in the gas phase

  7. e- e- e- e- e- 9+ 3+ e- e- e- e- e- e- e- Z* and its effect on size and IE Li F r = 71 pm > r = 152 pm Z*= 1.28 < Z*= 5.13 EA1 = 520 kJ/mol EA1 = 1681 kJ/mol <

  8. Periodic distribution of IE1 values List of the IE1 in kJ/mol for the elements IEincreases across the period Z* increases IEincreases up the group Shielding effect decreasesie.Z* increases

  9. Enthalpy of Electronic Attraction Energyreleased when an element attracts an extra electron into the lowest-energy unoccupied orbital to form an anion For large Z* e’s are held closely to the nucleus therefore e-n interactions will be stronger for an additional electron coming in. CompareLi (Z* = 1.28) with F (Z* = 5.13 ) Negative since energy is released DHEA always negative DHEAincreases in magnitude across period DHEAdecreases in magnitude down the group

  10. Electronegativity (c) i) How strongly does an element hold onto its own electrons ? ii) How strongly is an element able to attract electrons from other elements? A combination of ionization energyand enthalpy of electronic attraction. Which element(s) should have the highestelectronegativity? Which element(s) should have the lowestelectronegativity?

  11. Pauling Electronegativity General trend in element electronegativity

  12. The Periodic Table Dmitri Mendeleev, In 1869, noticed that elements exhibited similar behaviour, in groups, in the ratios in which they form molecules with H and O. Incomplete – noble gases are missing Blank spaces left for elements yet to be discovered. Elements arranged by increasing mass so that similar elements form columns In 1913, H.G.J. Moseley- the periodic table is more descriptive if the elements were in order of increasing atomic number rather than increasing mass. Order based on atomic mass causes misalignments.

  13. The Modern Periodic Table name & atomic weight Carbon 12.011

  14. “The properties of the elements are periodic functions of atomic number.” Law of Periodicity Group Period Similar chemical properties Repetition of properties Nonmetals – insulators not ductile Metalloids - Semiconductors Ductile ? Metals – Conducting, Ductile

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