Atomic Radius and Ionization Energy: Trends and Relationships

1. Background • Losing an electron is called ionization • An ion is an atom that has either a net positive or net negative charge • Q: what would the charge be on an atom that lost an electron? Gained two electrons? • A: +1 (because your losing a -ve electron) • A: -2 (because you gain 2 -ve electrons)

2. Atomic Radius Trend • Group Trend – As you go down a column, atomic radius increases As you go down, e- are filled into orbitals that are farther away from the nucleus (attraction not as strong) • Periodic Trend – As you go across a period (L to R), atomic radius decreases As you go L to R, e- are put into the same orbital, but more p+ and e- total (more attraction = smaller size)

3. Ionization Energy • Ionization Energy – energy needed to remove outermost e-

4. Ionization energy • Ionization energy is the energy required to remove one outer electron from an atom • Note: atomic radius is the distance from the nucleus to the outer electron shell • Ignore H when looking at trends, look at many periods/groups when summarizing trends • Group Trend – As you go down a column, ionization energy decreases • As you go down, atomic size is increasing (less attraction), so easier to remove an e-

5. Ionization Energy As you go down, atomic size is increasing (less attraction), so easier to remove an e- • Periodic Trend – As you go across a period (L to R), ionization energy increases As you go L to R, atomic size is decreasing (more attraction), so more difficult to remove an e- (also, metals want to lose e-, but nonmetals do not)

6. Ionization energy vs. atomic number

7. Atomic radius vs. atomic number

8. 11p+ 12n° 11p+ 12n° 10p+ 10n° 7. Na has 11 electrons Na+ has 10 electrons Ne has 10 electrons • electron configuration of Na+ resembles Ne • Alkali metals become like noble gases • Radius increases because shells are added • Increased radius will make it easier to lose an electron because of greater distance between positive and negative charges

9. 9. Proton # increases. More protons means greater attraction between nucleus and outer electron thus higher ionization energy. The greater attraction also means that outer electrons are brought closer to the nucleus, thus smaller atomic radius results. Li (enc = 1) Be (enc = 2) B (enc = 3) + + + + + + + + + + + +

10. 9. Proton # increases (1). More protons means greater attraction between nucleus and outer electron (1) thus higher ionization energy. The greater attraction also means that outer electrons are brought closer to the nucleus, thus smaller atomic radius results. Li (enc = 1) Be (enc = 2) B (enc = 3) + + + + + + + + + + + +

11. Reactivity • Reactivity – tendency of an atom to react • Metals – lose e- when they react, so metals’ reactivity is based on lowest Ionization Energy (bottom/left corner) Low I.E = High Reactivity • Nonmetals – gain e- when they react, so nonmetals’ reactivity is based on high electronegativity (upper/right corner)