Honors Chemistry

1. Honors Chemistry Chapter 8: Periodicity

2. 8.1 The Periodic Table • John Newlands (1864) • Arrange elements by mass • Properties repeat every 8th element • Law of Octaves • Ridiculed for musicalreference

3. 8.1 The Periodic Table • Dmitri Mendeleev (1869) • Periodic Law • Grouped elements byrepeating properties • Predicted properties of undiscovered elements • Problem – switched pairs of elements • Moseley – count by atomic #, not by mass

4. 8.2 Periodic Classification • Old vs. new numbering system • Representative Elements (main group) • Groups IA – VIIA, Unfilled s or p sublevels • Noble Gases • Group VIIIA, Filled p sublevel • Transition Metals • “B” Groups, Unfilled d sublevel • Lanthanides and Actinides • Unfilled f sublevel

5. 8.2 Periodic Classification • Valence Electrons • Electrons in outermost shell • Highest n quantum number reached • Involved in chemical bonding • Representing Free Elements • Metals – always use single atom (Na, Fe, Cu) • Most nonmetals – also monatomic (C, As, Kr) • Sulfur – actually S8, but we usually use just S • Phosphorous – exists as P4 • Diatomics – H2, N2, O2, F2, Cl2, Br2, I2

6. 8.2 Electron Configurations of Ions • Representative Elements • Try to get ns2 np6 (isoelectronic with noble gas) • Metals lose electrons (cations) • Nonmetals gain electrons (anions) • Find electron configurations of... • K+ • Al3+ • S2- • C4- • Sn2+

7. 8.2 Electron Configurations of Ions • Transition Metals • End with s2 dn • Remove the higher-level s electrons first = 2+ • Remove d’s one at a time until d5 or d0 • Often not isoelectronic with noble gas • Predict oxidation states of... • Fe • V • Cd • Ag

8. 8.3 Effective Nuclear Charge • Z = # of protons = nuclear charge • Decreases with distance from nucleus • Decreased by shielding effect • Zeff = Z – s • s = shielding constant • s increases with intervening shells

9. 8.3 Atomic Radius • “Size of an atom” • Half distance between adjacent nuclei • Radius increases down a group • Caused by increasing number of shells • Radius decreases across a period • Caused by increased Z on the same shells • Which is bigger: Ca or Sr? Ca or Zn?

10. 8.3 Atomic Radius

11. 8.3 Ionic Radius • Radius of a cation or anion • Anion (negative charge) – size increases • More electron repulsion • Cation (positive charge) – size decreases • Less electron repulsion • Isoelectronic ions • Size decreases with increasing positive charge • Size increases with increasing negative charge • Compare sizes of O2-, F-, Ne, Na+, Mg2+

12. 8.4 Ionization Energy • Minimum energy needed to remove an electron from an atom in its ground state • Measured in kJ/mol • Measures how tightly electrons are held • Multiple ionization energies • increases across a period • Increased nuclear force • decreases down a group • Increased dist. from nucleus

13. 8.4 Ionization Energy

14. 8.5 Electron Affinity • Measure of the energy change when an atom gains an electron • Measure of attraction for electrons • Also measured in kJ/mol • More difficult to measure than Eion • Same trends as Eion • increases across period • decreases down group

15. 8.6 Periodicity of Chemical Properties • Eion = atom’s attraction for its own e- • EA = atom’s attraction for other e- • Metals – low attraction – form cations • Nonmetals – high attraction – form anions • Diagonal relationships • Similarities between pairs in different groups • Likely caused by small size at the top of the group • Similar charge densities in cations

16. 8.6 Properties Across a Period • Need to compare similar compounds • Use oxides for comparison • Metal oxides • Ionic, High melting/boiling point • Basic • Nonmetal oxides • Molecular, Low melting/boiling • Acidic • Amphoteric • both acidic and basic prop.