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Electron affinity cont.

Electron affinity cont. As e- add to the same p sublevel of atoms with increasing nuclear charge. E- affinities become more negative across each period within the p block. Exception between groups 14 and 15

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Electron affinity cont.

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  1. Electron affinity cont. • As e- add to the same p sublevel of atoms with increasing nuclear charge. • E- affinities become more negative across each period within the p block. • Exception between groups 14 and 15 • Adding an e- to a carbon atom gives a half-filled p sublevel, this occurs more easily than forcing an e- to pair with another e- in an orbital of the already half-filled

  2. Group trends • E- add with greater difficulty down a group. • Because of an increase in effective nuclear charge down a group, which increases e- affinity. • Increase in atomic radius down a group, decreases e- affinities. • Exception – heavy transition metals, tend to be the same size or even decrease in radius down a group.

  3. Adding e- to negative ions • For an isolate ion in the gas phase, it is always more difficult to add a second e- to an already negatively charged ion. • Second e- affinities are all positive. • Certain p-block nonmetals tend to form negative ions that have noble gas configurations. • With halogens it is difficult to add another e- because they have noble gas configuration after becoming a negative one ion.

  4. Ionic radii • Cation – positive ion, loss of one or more electrons. – leads to decrease in atomic radius • Anion – negative ion, addition of one or more e-, leads to an increase in atomic radius. (positive charge remains the same)

  5. Period trends • Metals tend to form cations. • Nonmetals at the upper right tend to form anions. • Cationic radii decrease across a period because the e- cloud shrinks due to the increasing nuclear charge acting on the e-. • Anionic radii decrease across each period for the elements in groups 15-18. (same reason why cation radius decrease)

  6. Valence electrons • Electrons available to be lost, gained, or shared in the formation of chemical compounds. • Usually located in incompletely filled main-energy levels. • What sublevel are the valence e- located? • Group 1 and 2 • Transition elements • Group 13-18

  7. electronegativity • Linus Pauling devised a scale of numerical values reflecting the tendency of an atom to attract electrons. • Electronegativity – measure of the ability of an atom in a chemical compound to attract e- from another atom in the compound. • Most electronegative element is Flourine • Why not At?

  8. Period trends • Electronegativities tend to increase across each period • alkali and alkaline-earth metals are the least electronegative.

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