III. Periodic Trends, Part 2 (p. 140 - 154) Ch. 5 - The Periodic Table III. Periodic Trends, Part 2 (p. 140 - 154)

F. Electron Affinity Electron Affinity: the energy released when an electron is added to an atom to form a negative ion Cl + e-  Cl- + energy Electron affinity is the energy change associated with creating ANIONS (-). (E.A. is a measure of how much an atom wants to GAIN an electron.)

F. Electron Affinity Note the difference! Ionization Energy: the energy required to remove an electron to form a positive ion Na + energy  e- + Na+ Ionization energy is the energy change associated with creating CATIONS (+). (I.E. is a measure of how much an atom wants to LOSE an electron.)

F. Electron Affinity Electron Affinity increases up and to the right, but only to column 17. F Cl Br I At Noble gases have LOW E.A. because they already have full octets. (They don’t want to add an electron and/or gain a negative charge.)

F. Electron Affinity Increases to the RIGHT (up to group 17) in a period Increases UP in a group

F. Electron Affinity Why larger going up? Fewer energy levels = smaller radius = greater attractive force Why larger to the right? Increased valence & Zeff = greater attractive force Why low values for noble gases? They don’t WANT another electron– they already have full octets.

F. Electron Affinity If E.A. and I.E. have opposite definitions, why do the trend directions match? The elements that really want to gain an electron are usually the same elements that really DON’T want to lose an electron.

G. Electronegativity Electronegativity: the attraction of an atom for electrons shared in a bond When two atoms share electrons, the sharing is not always equal. The atom with greater e-neg pulls the shared electrons toward it, resulting in a polar (unequal) bond.

G. Electronegativity Increases to the RIGHT (up to group 17) in a period Increases UP in a group

G. Electronegativity Again, the trend only goes right to Group 17. The top 3 noble gases (the INERT gases) do not have electronegativity values, because they do not form bonds.

H. Reactivity Reactivity: the tendency of a substance to undergo chemical reaction, either by itself or with other materials, and to release energy. In general, reactivity increases as element get closer to a stable, full octet configuration. This makes reactivity greatest in Group 1 and Group 17, as they are closest to Group 18 (the noble gases).

H. Reactivity Metal reactivity (metallic character): is based on an element’s willingness to LOSE valence electrons. Increases down and to the left, as ionization energy becomes lower.

H. Reactivity Nonmetal reactivity (nonmetallic character): is based on an element’s ability to gain valence electrons. Increases up and to the right, as electron affinity becomes greater.

H. Reactivity Noble gases are UNREACTIVE. Reactivity increases: Down and left in the metals. Up and right in the nonmetals

Be or Ba Se or Br Ba Br Examples Which atom has the greater reactivity? Be or Ba Se or Br Ba Br

N or Bi F or Ne N F Examples Which atom has the higher electron affinity? N or Bi F or Ne N F

S or Cl Al or Ga Cl Al Examples Which particle has the greater electronegativity? S or Cl Al or Ga Cl Al