Periodic Properties of Elements Chapter 7 part I

Periodic trends in Orbitals

Periodic Trends in Electron Orbitals

Exceptions to the rules  Chromium and Copper do not follow the expected electron configuration.  Cr is expected to be [Ar]4s 2 3d 4  Cu is expected to be [Ar]4s 2 3d 9

Ionization energy  The energy required to remove one electron from a gaseous element or ion.

Ionization Energy (kJ/mol) 1st2nd3rd4th5th Li Be B C

Ionization energy  First ionization energy is the energy required to remove the highest energy electron.  As the number of protons increase, generally it is more difficult to remove an electron until a shell is completed.

Periodic Trends in Ionization Energy

Questions  Which of these atoms has the largest 1st ionization energy?  2nd?  Which has the smallest?  Why?  1s 2 2s 2 2p 6  1s 2 2s 2 2p 6 3s 1  1s 2 2s 2 2p 6 3s 2

Solution  Ne (1s 2 2s 2 2p 6 ) has the highest 1st ionization energy as it has a complete s p shell.  Na (1s 2 2s 2 2p 6 3s 1 ) has the lowest 1st due to shielding.  2nd: Highest Na+(1s 2 2s 2 2p 6 )  2nd: Lowest Mg+(1s 2 2s 2 2p 6 3s 1 ) due to shielding.  What is shielding?  Shielding is the description of a complete electron shell (core electrons) and its “neutralizing” of the positive charge of the nucleus. This causes outer shell electrons to be bound less strongly to the atom.

Electron Affinity  The energy change associated with the addition of an electron to an atom in its gaseous state.

Electron Affinity  Is often referred to as the energy released when an atom accepts an electron.  The more negative the number the more energy released.

Atomic radius  These values are obtained by measuring the distance between atoms in chemical compounds.  These values may be smaller than the 90% of the electron density. Why?

Atomic radius of ions  When electrons are added to an atom one would expect an increase in the radius.  One would also expect a decrease in radius when an electron is removed.

Atomic radius  But why does the radius of the atom decrease with each increase in atomic number???

Other trends: Metallic Character