The Periodic Table and Ionic Bonding: Part 5-Periodic Table Trends 1

Objectives -Describe what electron affinity is and how it is related to ion formation -Explain how trends in electron affinity are shown in the periodic table 2

Periodic Trend #4: Electron Affinity (E.A) Electron affinity- energy released when an atom gains an electron and the higher it is the greater attraction an atom had for it General Formula X (atom) + electron ---> X -1 (ion) + energy Specific Formula Cl + electron ---> Cl kcal/mole Negative ion with 1 more electron than proton A negative ion = anion Larger than the original atoms

ACROSS PERIODS electron affinity INCREASES to a maximum in Group VII then is a minimum in Group VIII ATOM: Na -> Cl Ar E.A.: > (kcal/mole) DOWN GROUPS electron affinity usually DECREASES due to the positive nucleus being less attracted to the electrons further away Periodic Trend #4: Electron Affinity (E.A)

Nonmetals will gain enough electrons to have a stable electron structure like a noble gas or core atom (s 2 p 6 ) Group VII atoms (s 2 p 5 ) gain 1 electron & form -1 ions Group VI atoms (s 2 p 4 )gain 2 electrons & form -2 ions Group V atoms s 2 p 3 )gain 3 electrons & form -3 ions Periodic Trend #4: Electron Affinity (E.A)

Atom e configuration Ion e configuration Cl 1s 2 2s 2 2p 6 3s 2 3p 5 Cl -1 1s 2 2s 2 2p 6 3s 2 3p 6 S 1s 2 2s 2 2p 6 3s 2 3p 4 S -2 1s 2 2s 2 2p 6 3s 2 3p 6 P 1s 2 2s 2 2p 6 3s 2 3p 3 P -3 1s 2 2s 2 2p 6 3s 2 3p 6 not stable stable [Ar] Periodic Trend #4: Electron Affinity (E.A)

Ion Summary GROUPIIIIIIIVVVIVIIVIII Electron Configuration Ends in: s1s1 s2s2 s2p1s2p1 s2p2s2p2 s2p3s2p3 s2p4s2p4 s2p5s2p5 s2p6s2p6 Electrons Lost Electrons Gained Ion Formed Remember that the group number tells you how many valence electrons there are!!! *Note – there are some exceptions to this chart!

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Exceptions 9 Exceptional elements The elements in this table can form more than one type of ion When naming these compounds, the type of ion is expressed in the name with a roman numeral These are all transition elements and they can form a variety of ions!

Relating IE, EA and Metallic Properties *Note – there are some exceptions High in metallic properties = low ionization energy = low electron affinity Low in metallic properties = high ionization energy = high electron affinity

Objectives -Describe what electron affinity is and how it is related to ion formation -Explain how trends in electron affinity are shown in the periodic table 11