Size of Atoms - Trends

Atomic Radii Li Na K Rb Cs Cl S P Si Al Br Se As Ge Ga I Te SbSn In Tl Pb Bi Mg Ca Sr Ba Be F O N C B IA IIA IIIA IVA VA VIA VIIA = 1 Angstrom

Li Na K Rb Cs La Xe Kr Zn Cl F He H 3d transition series 4d transition series atomic number atomic radius

Periodic Trends in Atomic Radii LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World, 1996, page 175

Relative Size of Atoms Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 350

Attraction and Repulsion of Electrical Charges ++ Particles with opposite charges attract one another. Particles with like charges repel one another

Coulombic Attraction Coulombic Attraction 1) Charge opposites attract like repels 2) Distance A B C D

Shielding Effect Kernel electrons block the attractive force of the nucleus from the valence electrons + nucleus Valence Electrons Electron Shield “kernel” electrons

Shielding Effect and Effective Nuclear Charge + _ _ _ Mg = [Ne]3s 2 attractions repulsions Hill, Petrucci, General Chemistry An Integrated Approach 2nd Edition, page 336 Mg

Decreasing Atomic Size Across a Period As the attraction between the (+) nucleus and the (–) valence electrons , the atomic size . Greater coulombic attraction. From left to right, size decreases because there is an increase in nuclear charge and Effective Nuclear Charge (# protons – # core electrons). Each valence electron is pulled by the full ENC (ENC = 1) (ENC = 2) + Li Be (ENC = 3) B 1s22s11s22s1 1s22s21s22s2 1s22s22p11s22s22p1 Li Be B

Sizes of ions: electron repulsion Valence electrons repel each other When an atom becomes a anion (adds an electron to its valence shell) the repulsion between valence electrons increases without changing ENC Thus, F – is larger than F Fluorine atom F 1s 2 2s 2 2p F 1- 1s 2 2s 2 2p 6 +1e Fluorine ionFluoride ion

Atomic Radius of Atoms Na K Rb Cs Cl S P Si Al Br Se As Ge Ga I Te SbSn In Tl Pb Bi Mg Ca Sr Ba Be F O N C B

Atomic Radii Li Na K Rb Cs Cl S P Si Al Br Se As Ge Ga I Te SbSn In Tl Pb Bi Mg Ca Sr Ba Be F O N C B IA IIA IIIA IVA VA VIA VIIA = 1 Angstrom IA IIA IIIA IVA VA VIA VIIA = 1 Angstrom Li 1+ Be 2+ Na 1+ Mg 2+ Ba 2+ Sr 2+ Ca 2+ K 1+ Rb 1+ Cs 1+ Cl 1- N 3- O 2- F 1- S 2- Se 2- Br 1- Te 2- I 1- Al 3+ Ga 3+ In 3+ Tl 3+ Ionic Radii

Atomic Radii Li Na K Rb Cs Cl S P Si Al Br Se As Ge Ga I Te SbSn In Tl Pb Bi Mg Ca Sr Ba Be F O N C B IA IIA IIIA IVA VA VIA VIIA = 1 Angstrom He Ne Ar Kr Xe Rn VIIIA

IA IIA IIIA IVA VA VIA VIIA = 1 Angstrom Li 1+ Be 2+ Na 1+ Mg 2+ Ba 2+ Sr 2+ Ca 2+ K 1+ Rb 1+ Cs 1+ Cl 1- N 3- O 2- F 1- S 2- Se 2- Br 1- Te 2- I 1- Al 3+ Ga 3+ In 3+ Tl 3+ Ionic Radii

Trends in Atomic and Ionic Size Li Na K 60 Li + 95 Na+ 133 K+ e e e F-F- 136 Cl Br F Cl Br e e e MetalsNonmetals Group 1 Al e e e Group 13 Group 17 Cations are smaller than parent atomsAnions are larger than parent atoms Al 3+

152 Li 60 Li + e Li + e e e e Li Lithium atom Lithium ion Li Lithium atom Li Energy

IA IIA IIIA IVA VA VIA VIIA Li 1+ Be 2+ Na 1+ Mg 2+ Cl 1- N 3- O 2- F 1- S 2- Se 2- Br 1- Te 2- I 1- Al 3+ Ga 3+ In 3+ Tl 3+ Ca 2+ K 1+ Sr 2+ Rb 1+ Cs 1+ Ba 2+ Li Na K Rb Cs Cl S P Si Al Br Se As Ge Ga I Te SbSn In Tl Pb Bi Mg Ca Sr Ba BeBCNOF = 1 Angstrom Atomic Radii Ionic Radii Cations: smaller than parent atoms Anions: LARGER than parent atoms

The Octet Rule and Common Ions Oxygen atom O 1s 2 2s 2 2p 4 Fluorine atom F 1s 2 2s 2 2p 5 Sodium atom Na 1s 2 2s 2 2p 6 3s 1 Magnesium atom Mg 1s 2 2s 2 2p 6 3s Oxygen ion O 2- 1s 2 2s 2 2p 6 Fluorine ion F 1- 1s 2 2s 2 2p 6 Sodium ion Na 1+ 1s 2 2s 2 2p 6 Magnesium ion Mg 2+ 1s 2 2s 2 2p Neon atom Ne 1s 2 2s 2 2p 6 +1e - -1e - -2e - +2e

Isoelectronic Species Oxygen ion O 2- 1s 2 2s 2 2p 6 Fluorine ion F 1- 1s 2 2s 2 2p 6 Sodium ion Na 1+ 1s 2 2s 2 2p 6 Magnesium ion Mg 2+ 1s 2 2s 2 2p Neon atom Ne 1s 2 2s 2 2p 6 Isoelectronic Isoelectronic - all species have the same number of electrons. Can you come up with another isoelectronic series of five elements? p = 8 n = 8 e = 10 p = 9 n = 9 e = 10 p = 10 n = 10 e = 10 p = 11 n = 11 e = 10 p = 12 n = 12 e = 10

Lewis Structure Na Cl X oo oo o o o HCN o X X X X      Na H CN Cl Na H CN Gilbert Lewis “Lewis Dot Notation”

Atomic Radius vs. Atomic Number Li Na K Rb Cs La Xe Kr Zn Cl F He H 3d transition series 4d transition series atomic number atomic radius