Periodic trends

Atomic Radius Atomic radius is the distance from the center of an atom’s nucleus to its outermost electron. Radius

Atomic Radius Trend #1 Shielding Effect Hydrogen (1s1) Atoms get larger going down a group Lithium (1s2 2s1) Sodium (1s2 2s2 2p6 3s1) Shielding Effect

Atomic Radius Trend #2 1s2 2s2 2p2 1s2 2s2 2p1 1s2 2s2 2p3 Shrinking Effect

Atomic Radii of Representative Elements (nm) Li Be B C N O F Na Mg Al Si P S Cl K Ca Ga Ge As Se Br Sr Rb In Sn Sb Te I Cs Ba Tl Pb Bi Po At

Atomic Radius Atomic Radius increases Atomic Radius increases H Li K F Na K Fr F At Atomic Radius increases

Ionization Energy A + E A+ + e- Energy needed to remove one of atom’s electrons from its outermost shell A + E A+ + e- Reflection of how strongly an atom holds onto its outermost electron. Atoms with high ionization energies hold onto their electrons very tightly. Atoms with low ionization energies are more likely to lose one or more of their outermost electron.

Ionization Energy Ionization energy increases H Li Na K Fr F At Ionization energy increases Ionization energy increases

Metallicity Ability of an atom to lose an electron TREND: Increases from top to bottom Decreases from left to right

Electron Affinity A + e- A- + E Energy released when an atom gains an electron to form a negative ion/anion. A + e- A- + E Measure of an atom’s attraction, or affinity, for an extra electron. Electron affinity increases within a period from left to right. As one goes down a group, electron affinity decreases.

Electronegativity Ability of an atom to attract electrons in a chemical bond. H Li Na K Fr F At Electronegativity increases Electronegativity increases

Ionic Radius Anion (negative ion), its size increases, since the nuclear charge remains the same but the repulsion resulting from the additional electron(s) enlarges the domain of the electron cloud.

Ionic Radius Cation (positive ion) smaller than neutral atom, since removing one or more electrons reduces electron-electron repulsion but the nuclear charge remains the same, so the electron cloud shrinks. From top to bottom of a periodic group both the atomic radius and the ionic radius increases.

+ Ionic Radius Li F Li+ F-- Changes in size when Li reacts with F to form LiF

Tl Pb Ionic Radii of Representative Elements (nm) Rb Cs 1A 2A 3A 4A 5A Li Be O F B C P S Na Cl Mg Al Si As Se K Br Ca Ga Ge Sb Te Rb I Sr In Sn Bi Po Cs At Ba Tl Pb

Summary of Periodic Trends Metallicity inreases Atomic Radius increases/ Ionic size H Li Na K Fr F At Electronegativity increases Electron affinity increases Ionization energy increases Metallicity increases Atomic Radius increases/ ionic size Electronegativity increases Ionization energy increases Electron Affinity increases

Challenge Arrange the following groups of atoms in order of decreasing atomic size: B, Al, Ga Sn, Sb, Te Cd, Si, Ga As, P, Cl

Answers a. Ga, Al, B b. Sn, Sb, Te c. Cd, Ga, Si d. As, P, Cl e. Cl, O, F

Challenge 2. For each of the following pairs, predict which element has (1) the larger radius, and (2) the larger ionization energy: Na & Cl C & O Li & Rb As & F Ne & Xe N & Sb Sr & Si Fe & Br

Answers (1) Na, (2) Cl (1) C, (2) O (1) Rb, (2) Li (1) As, (2) F (1) Xe, (2) Ne (1) Sb, (2) N (1) Sr, (2) Si (1) Fe, (2) Br

Challenge 3. List the following ions in order of increasing ionic radius: N3-, Na+, F-, Mg2+, O2- 4. Indicate which one of the two species in each of the following pairs is smaller: Cl or Cl- Na or Na+ O2- or S2- Mg2+ or Al3+ Au+ or Au3+