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ATOMS, MOLECULES, AND IONS Atomic Theory of Matter Modern atomic theory is based on the experimental work of many scientists over the course of many th years. Experimentation done as early as the 18 century resulted in generalizations which are summarized in what are called “laws”. Dalton’s Atomic Theory of Matter — ♦ ♦ ♦ ♦ ♦ Matter consists of individual atoms. All atoms of a given chemical element are identical. Different chemical elements have differing atoms of different mass. Atoms are indestructible – they retain their identity in reactions. Compounds are formed from a combination of elements in small whole number ratios. The Law of Constant Composition — the relative kinds and numbers of atoms are constant for a given compound. (e.g. water, H2 O, always contains 2 hydrogen atoms and 1 oxygen atom) The Law of Conservation of Mass — during a chemical reaction, the total mass before reaction is equal to the total mass after reaction. N2 + 3 H 2 → 2 NH 3 34 g 34 g The Law of Multiple Proportions — if two elements A and B combine to form more than one compound, then the mass of B that combines with the mass of A is a ratio of small whole numbers. (e.g. CO, CO2 ) Modern View of Atomic Structure Experiments by Thomson and Millikan confirmed the existence of electrons as the negatively charged –19 particles within an atom. Electrons have a charge of e = 1.6021773 × 10 C and a mass of –31 9.109390 × 10 kg. Later experiments by Rutherford determined that at the center of an atom is a positively charged, compact, heavy nucleus. The charge on the atomic nucleus is +Ze (Z is the atomic number of the atom). The fundamental unit of positive charge in the nucleus is the proton. ♦ Chemical identity of an atom is determined by the number of protons. ♦ The nucleus also contains neutral particles, neutrons, which are essential for the stability of the nucleus. They contribute to the mass of the atom but have no charge. Atomic Mass Units Angstroms (Å) Isotopes, Atomic Numbers, and Mass Numbers Z= N= A= Ex. 1 An isotope detected in a mass spectrometer has atomic number 82 and relative mass 205. Write the symbol for this isotope, and list the subatomic particles composing it. The Periodic Table Molecules and Molecular Compounds Chemical Formulas Empirical and Molecular Formulas Empirical Formula Molecular Formula Ex. 2 From the following list, find the groups of compounds that have the same empirical formula: C2H2, N2O4, C2H4, C6H6, NO2, C3H6, C4H8 Ions and Ionic Compounds A cation results when an atom or molecule loses electrons (giving it a positive charge). An anion results when an atom or molecule gains electrons (giving it a negative charge). Ionic Charges and Ionic Compounds Ex. 3 Predict formulas for compounds formed from a. Polonium (Po) and strontium (Sr) 2+ 3– b. Mg and PO4 c. Gallium (Ga) and fluorine (F) Naming Inorganic Compounds Ionic Compounds Cations Anions Ionic Compounds Acids Binary Molecular Compounds Ex. 4 Many familiar substances have common, unsystematic names. For each of the following, give the correct systematic name: a. saltpeter (KNO3) b. c. d. soda ash (Na2CO 3) lime (CaO) muriatic acid (HCl) e. Epsom salts (MgSO4) f. milk of magnesia (Mg(OH)2) Nomenclature Rules for Polyatomic Ions Polyatomic Oxoanions with Standard Names Key Element Formula Nitrogen NO3 NO2 SO4 Sulfur nitrate ion − nitrite ion 2– 2– − HSO3 Phosphorus PO4 sulfate ion hydrogen sulfate ion sulfite ion hydrogen sulfite ion − HSO4 SO3 Name of Ion − 3– phosphate ion hydrogen phosphate ion dihydrogen phosphate ion phosphite ion HPO4 2– H2 PO4 – 3– PO3 2– CO3 Carbon HCO3 Chlorine ClO4 ClO3 ClO2 carbonate ion hydrogen carbonate ion − – perchlorate ion chlorate ion chlorite ion hypochlorite ion – – – ClO Boron BO3 3− borate ion Polyatomic Ions with Non-Standard Names Key Element Carbon Formula − − NH 4 2– + H3 O hydronium ion hydroxide ion peroxide ion superoxide ion – OH O2 Metals 2– – MnO4 CrO4 oxalate ion ammonium ion + O2 acetate ion cyanide ion C2 O4 Oxygen – C2 H3 O2 (CH3 COO ) CN Nitrogen Name of Ion – 2– Cr2 O7 2– permanganate ion chromate ion dichromate ion Names of Common Acids Binary Acids Oxoacids Organic Acids HF hydrofluoric acid HClO4 perchloric acid HCOOH formic acid HCl hydrochloric acid HClO3 chloric acid CH3 COOH acetic acid HBr hydrobromic acid HClO2 chlorous acid C6 H5 COOH benzoic acid HI hydroiodic acid HClO hypochlorous acid HOOC–COOH oxalic acid HCN hydrocyanic acid H2 SO4 sulfuric acid H2 S hydrosulfuric acid H2 SO3 sulfurous acid HNO3 nitric acid HNO2 nitrous acid H3 PO4 phosphoric acid H2 CO3 carbonic acid Ex. 5 Ex. 6 Iodic acid has the molecular formula HIO3. Write the formulas for the following: a. the iodate anion b. the periodate anion c. the hypoiodite anion d. hypoiodous acid e. periodic acid From the following list of elements – Ar, H, Ga, Al, Ca, Br, Ge, K, O – pick the one that best fits each description; use each element only once: a. an alkali metal b. an alkaline earth metal c. a noble gas d. a halogen e. a metalloid f. a nonmetal listed in group IA g. a metal that forms a 3+ ion h. a nonmetal that forms a 2– ion i. an element that resembles aluminum