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Chapter Two: Atoms, Molecules & Ions Atomic Theory & Structure Isotopes, Numbers & Masses Periodic Table Molecules, Ions, Compounds & Formulas Naming Species Atomic Theory and Structure What is the smallest piece of matter possible? Democritus called the smallest particles “atomos” Dalton’s atomic theory of matter: -elements are composed of small particles -- atoms -all atoms of an element are identical -atoms are not created or destroyed chemically -compounds formed by chemical combination of two or more elements -a given compound has same relative number & type of atoms (law of constant composition) -atoms retain character during chemical rxns. only undergo rearrangement (conservation of matter) Law of Multiple Proportions If two elements, A & B, form more than one compound, the masses of B that can combine with a given mass of A are in a ratio of small whole numbers carbon dioxide 12 g of Carbon & 32 g of Oxygen O 2x 12 g of Carbon & 16 g of Oxygen C O carbon monoxide C O Subatomic Particles -J.J. Thompson determined charge:mass ratio of e-, 1897 -Robert Millikan measured charge of e-, 1909 -Thompson developed “plum pudding” model of atom -Rutherford developed “nuclear” model of atom alpha particle source detector Modern Atomic Structure PARTICLE CHARGE * MASS (AMU) Proton +1 1.0073 Neutron 0 1.0087 Electron -1 5.486 x 10-4 * unit charge = 1.602 x 10-19 C (coulomb) amu (u) -- atomic mass unit = 1.66054 x 10-24 g Atomic Number number of protons in an atom defines an element shown as the symbol subscript 6C Mass Number total number of protons plus neutrons will vary between isotopes shown as the symbol superscript 12C Isotopes elements which have the same atomic number but different mass numbers 12C 6 13C 6 14C 6 are isotopes Periodic Table –Allows for organization of elements –Allows for grouping of elements in terms of physical and chemical characteristics Metals, Non-metals & Metalloids –Group 1A Alkali Metals –Group 2A Alkaline Earth Metals –Group 6A Chalcogens –Group 7A Halogens –Group 8A Nobel Gases –B Groups Transition Metals Know these !! Molecules and Molecular Compounds •Molecule — the smallest particle of a compound that can be identified as that compound — chemical combination of two or more atoms — a pure substance • Chemical Formula — a symbol representation of a molecule/compound — shows the type and ratio of atoms in a molecule type is given by symbol ratio is given by a subscript to right of symbol Examples: Molecule Ratio H2O 2:1 heteroatomic H2O2 2:2 heteroatomic CO2 1:2 heteroatomic CO 1:1 heteroatomic O2 - homoatomic • Formulas —Molecular Formulas Give the type and exact number of each type of atom —Empirical Formulas Give only the type and simplist ratio of atoms Molecular Formula H2O Empirical Formula H2O H2O2 HO C6H6 CH C2H6 CH3 — Structural Formulas Show which atoms are attached to which atoms C2H6O H H H C O C H H H dimethylether H H H C C H H ethanol O H Ions & Ionic Compounds • Some elements will either lose or gain one or more electrons to become charged species • Metals – typically lose electrons, become +, cations • Non-Metals – typically gain electrons, become -, anions Monatomic Ions – made from a single element • Na Na+ + 1e• Cl + 1e- Cl- 11 p+ 11 e- 17 p+ 17 e- 1e- Na Cl + 1e- + Na+ Cl- 11 p+ 10 e- 17 p+ 18 e- Hints to Determine Ion Charges • Hydrogen +1 • Oxygen -2 • Group IA +1 • Group IIA +2 • Group VIA -2 • Group VIIA -1 Polyatomic Ions -- “molecules” which have a net positive or negative charge – CO32– NH4+ – OH- carbonate ion ammonium ion hydroxide ion Prediction of Charges -- all species tend toward the most stable state – Nobel gases are very stable – Elements add or lose electrons to “mimic” nobel gases Ionic Compounds • Oppositely charged ions form ionic compounds – held together by ionic bonds due to the electrostatic attraction between the opposite charges • Ionic compounds are always neutral species • Mg2+ and or Mg2Cl Cl- form MgCl2 not MgCl Naming Inorganic Compounds • Names of Monatomic Ions – cations are named for the elements Na+ is sodium ion Fe+2 is iron(II) ion (ferrous ion) Cu+ is copper(I) ion (cuprous ion) Al+3 is aluminum ion Fe+3 is iron(III) ion (ferric ion) Cu2+ is copper(II) ion (cupric ion) – anions are named for the root name of the element with the ending -ide O-2 is oxide ion H- is hydride ion Cl- is chloride ion N-3 nitride ion •Naming Polyatomic Ions • Know the names, charges and formulas of the important polyatomic ions – NH4+ ammonium ion – CO3-2 carbonate ion – SO4-2sulfate ion – OH- hydroxide ion – NO3- nitrate ion • Polyatomic ions are treated as separate entities or units • Naming and formula rules are the same as for compounds with monatomic ions Naming Binary Ionic Compounds • Cations always named first • Anions always named last – NaCl sodium chloride – BaCl2 barium chloride • for cations which have more than one possible charge, the charge of the ion must be given in the name – Fe2O3 – FeO iron(III) oxide iron(II) oxide • Combinations must be neutral! • Examples: – 2 Na+ and Na2CO3 1 CO3-2 is sodium carbonate – 2 NH4+ and 1 S-2 (NH4)2S is ammonium sulfide – 1 Ba+2 and 2 OHBa(OH)2 is barium hydroxide – 3 Mg+2 and 2 PO4-3 is magnesium phosphate Mg3(PO4)2 – 1 Na+ , 1 H+ and 1 CO3-2 is sodium hydrogen carbonate or sodium bicarbonate, NaHCO3 Acids • A compound that produces hydrogen ions (H+) when dissolved in water • tastes sour • turns litmus red • has a pH less than 7 • typically the formula begins with one or more H’s – HCl(aq) – H2SO4(aq) – HC2H3O2(aq) hydrochloric acid sulfuric acid acetic acid Binary Acids • Acids which contain H and another nonmetallic element • Naming -- to the root name of the nonmetallic element: – add the prefix hydro– add suffix -ic acid • HF(aq) hydrofluoric acid • HBr(aq) hydrobromic acid • HCl(aq) hydrochloric acid Note! Oxyacids • Acids which contain H and O and another element (or H and a polyatomic anion containing O) • Naming -- to the polyatomic ion name – if the suffix is -ate, change it to -ic – if the suffix is -ite, change it to -ous – add acid to the end of the name • HNO3 nitric acid HNO2 nitrous acid • H2SO4 sufuric acid H2SO3 sulfurous acid • You must know polyatomic ion Binary Molecular Compounds • Chemical combinations of non-metals and nonmetals (no ions involved) • The more metallic element is named first • The second element (less metallic) is named with the ending -ide • Because there are no ions to use to determine relative ratio of atoms we must indicate the number of each atom by a prefix – N2O3 dinitrogen trioxide – SO3 sulfur trioxide Name the Following: • CaI2 calcium iodide • Cu2O copper(I) oxide • CuO copper(II) oxide • Cl2O7 dichlorine heptaoxide • HClO3 chloric acid note Write Formulas for the Following: • calcium hypochlorite Ca(ClO)2 • Mg+2 and ClO2- Mg(ClO2)2 • carbon tetrachloride CCl4 • NH4+ and SO4-2 (NH4)2SO4