Zumdahl’s Chapter 2

1. Zumdahl’s Chapter 2 Atoms, Molecules, and Ions

2. History of Chemistry Mass & Proportions Dalton Theory Subatomic Particles Structure of the Atom Molecules and Ions Periodic Table Symbols and Organization Naming Compounds Binary ionic molecule Binary covalent compounds Polyatomic ions Chapter Contents

3. History of Chemistry • Democritus (5th Century BC) atomic postulate • Lucretius (1st Century AD) “atoms and the void” • Priestly (18th Century AD) discovers oxygen • Lavoisier (18th) diamond=carbon

4. Conservation of Mass and Chemical Proportions • Mass unchanged in chemical reactions • Implies atoms conserved in reactions • Elements combine in definite, simple proportions by mass. •  Molecules are • atoms in definite • proportions! - Dalton

5. John Dalton (1808) • Elements are collections of identical, miniscule atoms. • Different elements differ in their atoms. • Compounds are combinations of different elements. • Under reaction, compounds rearrange their atoms.

6. Subatomic Components • J.J. Thompson (1897) “cathode rays are electrons” (e–) and finds e/m ratio • Robert Millikan (1909) measures e and hence melectron known at 9.1110-31 kg • E. Rutherford (1906) bounces  (He2+) off Au tissue proving protons (p+) in nucleus • F.A. Aston (1919) “weighs” atomic ions • J. Chadwick (1939) observes neutrons (no charge) by decomposition (to p+, e–, and ).

7. Structure of the Atom • Nucleons (protons and neutrons) of almost the same mass (1.6710-27 kg) live in nucleus (R~2 fm). • Electrons occupy the full atomic radius (R~50 pm), shielding the nucleus. • Electron and proton count identical in neutral atom.

8. 3579Br Z=35 is bromine’s atomic number (count of protons) A=79 is its mass number (count of all nucleons) So 3579Br has 79–35 or 44 neutrons 3581Br exist too in equal #s. So isotope average A=80 Symbology of an Atom

9. Molecules and Ions • Atoms in molecules share (covalent) or steal (ionic) electrons to bond. • Stolen electrons lead to attraction of unlike charged ions (ionic bonding) • Directional electron “clouds” lead to molecular shapes. • Molecules can be ionic as well as atoms.

10. Z increases linearly from 1H upper left Groups (columns) have similar chemistry Alkali metals, alkaline earths, transition metals, halogensandnoble gases Periodic Table

11. IONIC Cation named first. If atom 1 makes only one cation: Strontium chloride SrCl2 If atom 1 makes several cations: Iron(III) chloride FeCl3 COVALENT Less electronegative element named first Most electronegative gets “anionic” –ide Greek prefixes show proportions: Dichlorine heptoxide Cl2O7 Mono prefix is never used for first atom. Naming Compounds

12. Polyatomic Ions • Few polyatomic cations • Most common: ammonium (NH4)+ • Many polyatomic anions • NO3– nitrate, C2O42– oxalate, HSO4– hydrogen sulfate, H2PO4– dihydrogen phosphate, Cr2O72– dichromate • ClO–hypochlorite, ClO2– chlorite, ClO3– chlorate, ClO4–perchlorate

13. Al2(S2O3)3 P4O10 Cu(NO2)2 NaMnO4 CS2 Fe2(CrO4)3 HCl (gas) PH4BrO2 Aluminum thiosulfate Tetraphosphorous decaoxide Copper(II) nitrite Sodium permanganate Carbon disulfide Iron(III) chromate Hydrogen chloride Phosphonium bromite Naming Exercise