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Understanding Atomic Theory and Structure of Matter in Chemistry

This chapter delves into the foundations of atomic theory and the structure of matter. We explore the contributions of early thinkers like Democritus and Aristotle, followed by Proust and Lavoisier's laws, including the Law of Definite Proportions and the Law of Conservation of Mass. Key modern discoveries by Thomson, Millikan, Rutherford, and Chadwick about electrons, protons, and neutrons shape our understanding of atomic structure. The chapter also covers isotopes, the periodic table, and the basics of molecules and ions, equipping you with essential knowledge in chemistry.

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Understanding Atomic Theory and Structure of Matter in Chemistry

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  1. Honors Chemistry Chapter 2: Atoms and Molecules

  2. 2.1 Atomic Theory • Ancient Greeks • Democritus – matter is discontinuous (atomos) • Aristotle – matter is continuous (hyle) • Joseph Proust (1799) • Law of Definite Proportions – samples of a compound are always composed of the same proportion by mass • Antoine Lavoisier • Law of Conservation of Mass

  3. 2.1 Atomic Theory • John Dalton (1803) • Elements are made of indivisible particles (atoms) which are identical • Compounds are composed of atoms of more than one element combined in whole-number ratios • Chemical reaction involves rearranging atoms, not creating or destroying them • Law of Multiple Proportions • Elements can form different compounds by combining in many whole-number ratios

  4. 2.2 Structure of the Atom • J. J. Thomson (1897) • Cathode Ray Tube Experiments • Discovered electron • e/m = -1.76 x 1011 C/kg • Plum Pudding Model • Robert Millikan (1908) • Resolved e/m ratio • Oil Drop Experiment • ee = -1.6022 x 10-19 C • me = 9.11 x 10-31 kg

  5. 2.2 Structure of the Atom • Radioactivity • Wilhelm Roentgen – discovered x-rays • Antoine Becquerel – discovered radioactivity • a, b, and g radiation • The Proton • Discovered in modified CRT (canal rays) • ep = +1.6022 x 10-19 C • mp = 1.67262 x 10-27 kg • The Neutron • Discovered by James Chadwick • mn = 1.6794 x 10-27 kg

  6. 2.2 Structure of the Atom • Ernst Rutherford (1910) • Attempt to find better model of the atom • Gold Foil Experiment • Performed by Geiger and Marsden • Discovered a nucleus in the atom • The Planetary Model • Nucleus composed of p+ and n • e- orbit nucleus • Held by electrostatic force

  7. 2.3 Particles and Isotopes • Atomic Number (Z) • Number of protons • Mass Number (A) • Number of protons + neutrons

  8. 2.3 Particles and Isotopes • Nuclear Symbols • 7← mass number Li3← atomic number • Protons = 3 • Electrons = 3 (same as p+ in neutral atom) • Neutrons = 7 – 3 = 4 • Listing Z is redundant and often not done • Isotopes • Same element, different mass number • Example: 35Cl and 37Cl

  9. 2.4 Periodic Table

  10. 2.4 Periodic Table • Navigating the Table • Period – row across the table • Group (or Family) – column down the table • Metals, nonmetals, and metalloids • Family Names • IA – Alkalai Metals • IIA – Alkaline Earth Metals • “B groups” – Transition Metals • VIA – Chalkogens • VIIA – Halogens • VIIIA – Noble Gases • Lanthanides and Actinides

  11. 2.5 Molecules and Ions • Molecules • Neutral atoms bonded together • Diatomic molecule – contains 2 atoms • H2, N2, O2, F2, Cl2, Br2, I2 • Ions • Atom or group of atoms with a charge • Cation – positive charge • Anion – negative charge • Monatomic ion – single atom • Polyatomic ion – group of atoms

  12. 2.5 Molecules and Ions • Monatomic Cations (metals) • Group IA: 1+ • Group IIA: 2+ • Group IIIA: 3+ (B and Al only) • Transition and Post-transition metals: • Ag: + Zn, Cd: 2+ • Most others can form multiple charges • Cu+ = copper (I) Cu2+ = copper (II) • Cuprous Cupric

  13. 2.5 Molecules and Ions • Monatomic Anions (nonmetals) • Group VIIIA: no charge (noble gases) • Group VIIA: 1- • Group VIA: 2- • Group VA: 3- • Group IVA: 4- • H: 1- • No Roman numerals! • Change ending to -ide

  14. 2.5 Molecules and Ions • Polyatomic ions • Oxoanions (element with oxygen): • First one discovered: change ending to –ate • -ite, per-, and hypo- used for other oxoanions • ClO4- perchlorateClO3- chlorateClO2- chloriteClO- hypochlorite • not all exist for every element • e.g., for N, nitrate and nitrite exist, but no others

  15. 2.5 Molecules and Ions • 1+ • NH4+ ammonium • Hg22+ mercury (I) • 1- • OH- hydroxide • CN- cyanide • MnO4- permanganate • SCN- thiocyanate • HCOO- formate • CH3COO- acetate • NO3-, FO3-, ClO3-, BrO3-, IO3-

  16. 2.5 Molecules and Ions • 2- • O22- peroxide • C2O42- oxalate • S2O32- thiosulfate • Cr2O72- dichromate • CO32-, SiO32-, CrO42-, SO42- • 3- • PO43-, AsO43-

  17. 2.6 Chemical Formulas • Molecular Formula • Molecular Formula – true formula for a molecule • Exact number of atoms in the molecule • E. g., O2, O3, NH3 • Structural formula – shows how atoms are attached to each other • H |H – N – H • Empirical Formula – shows simplest ratio of atoms • C6H12O6 CH2O

  18. 2.6 Chemical Formulas • Ionic Compounds • Two or more ions stuck together • Charges must neutralize • Sodium chloride = Na+ and Cl- • Equal charges, so NaCl • Magnesium chloride = Mg2+ and Cl- • Need 2 Cl-’s to cancel out each Mg2+ • MgCl2 • Simplify when needed, e. g., lead (IV) oxide • Try these: aluminum sulfide, iron (III) nitrate

  19. 2.7 Naming Compounds • Ionic Nomenclature • Name the ions involved! • K2SO4 = potassium sulfate • Try these: K2O, Ba(ClO3)2, CaCO3, FePO4 • Molecular Nomenclature • -ide ending • Greek prefixes for numbers: • Mono-, di-, tri-, tetra- penta-, hexa-, hepta-, octa-, nona-, deca- • Try these: CO2, CCl4, H2O, SO3, UF6

  20. 2.7 Naming Compounds • Acids • Produce H+ ions in water solution • Binary acids = hydro – ic acid • HCl = hydrochloric acid • Oxoacids = change ending of anion • -ate  -ic HClO3 = chloric acid • -ite  -ous HClO2 = chlorous acid • Some polyatomic anions are treated as binary • Try these: • HBr, HNO3, H2SO3, HClO4, CH3COOH

  21. 2.7 Naming Compounds • Bases • Produce OH- ions in water solution • Named as any other ionic compound • NaOH = sodium hydroxide • Ammonia (NH3) also produces OH- ions in water • Hydrates • Compounds with water molecules attached • BaCl2∙ 2 H2O barium chloride dihydrate • Try this: CuSO4∙ 5 H2O

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