Chapter 2 Atoms, Molecules, and Ions

Transcription

1 hapter 2 Atoms, Molecules, and Ions 2.1 The Atomic Theory of Matter Is there such thing like a indivisible particle of matter (atom)? Based on the following observations: 1. Law of conservation of mass/matter (Antoine Lavoisier). 2. Law of constant composition/definite proportions. (Joseph Proust). Dalton s Atomic Theory (page 42). What makes a good theory? ow was Dalton s theory a good theory? 2.2 The Discovery of Atomic Structure J. J. Thomson s experiment in Describe the experiment, its results and meaning. e found the charge/mass ratio. ow? e m = /g Robert Millikan determined the charge on the electron in Describe the experiment, its results and meaning. e = and then the mass would be: Based on his findings, Thomson came up with the Plum Pudding Model of the atom. Describe the model and reasoning behind it. Radioactivity (1896): the spontaneous emission of radiation by an atom. Three types of radiation were discovered. ow can you tell the charge and relative mass of the different particles? particles particles rays Ernest Rutherford s Experiment (1911). Describe the experiment, his findings and the reasoning behind the atomic model he proposed (the nuclear model). 1

2 2.3 The Modern view of Atomic Structure Protons were discovered by Rutherford in Neutrons were discovered by James hadwick in The Nuclear Atom Particle harge harge (Atomic Mass Mass (Atomic Relative Mass Scale) Scale) Proton (p + ) x x kg Neutron (n 0 ) x kg Electron (e - ) x x kg x Atoms have no net electrical charge. What does this mean? Isotopes Atomic number (Z) = # p + Mass number (A) = # p + + # n 0. Isotopes are atoms with the same Z, but different A ; 6 ; 6 ; 6 Isotope symbol Mass Number A Atomic Number ZX (Element s symbol) For arbon or (sometimes Z is omitted) Problem 1 Q. Give the number of each type of particle (p +, n 0 and e - ) for the following isotopes. a P b. O 18 8 Q. Write the isotope symbol for an atom of nickel (Z = 28) containing 32 neutrons. 2.4 Atomic Weights Atomic Mass Units (amu) are a more convenient unit: 1 amu = g An atom of -12 weighs exactly 12 amu. All other masses are measured relative to

3 The Periodic Table Shows a Weighted Average Example: hlorine. Atomic Weight = (isotope mass) (fractional isotope abundance) Atomic Weight = (35 amu ) + (37 amu ) = amu Example alculate the weighed-average atomic mass of Magnesium. Mg amu 78.99% amu 10.00% amu 11.01% % Mass spectrometer (p.52). What is the principle behind it and what information does it provide? Problem 2 Neon has the following three stable isotopes: Isotope Mass (amu) % Abundance 20 10Ne ? 21 10Ne % alculate the missing percent abundances Ne ? 3

4 2.5 The Periodic Table What is periodicity? ow do you know which elements are metallic, nonmetallic and semimetals and which are their properties? What elements are found as gases, liquids or solids at room temperature? 2.6 Molecules and Molecular ompounds What are molecules? Some compounds are molecular. ow can you tell? What information does a molecular formula provide? ertain elements occur as 2 atom molecules (diatomic). rule of 7 s (Memorize them!) Other elements occur as polyatomic molecules. P4, S8, Se8 Types of Formulas. What is the difference between empirical and molecular formulas? Empirical Formula Molecular Formula 66 (Benzene) 22 (Ethene) What information does a structural formula provide? What is the advantage of a perspective formula or 3D formula? 4

5 2.7 Ions and Ionic ompounds ow are ions formed? What is a cation and what is an anion? Ion harge and the Periodic Table The charge on an ion can often be determined from an element s position on the Periodic Table Metals always form positively charged ions (cations) For many main group metals, the charge = the group number Nonmetals form negatively charged ions (anions) For nonmetals, the charge = the group number 8 What is the origin of the charge of a particular atom? Practice What is the charge on each of the following ions? potassium cation sulfide anion calcium cation bromide anion aluminum cation ow can you identify an ionic compound? Formulas of ionic compounds Ions Present Formula ow do we know how many ions of each type are present? If the subscripts are not the lowest whole-number ratio, divide them by the greatest common factor. Formulas of Ionic ompounds Ions Formula Ions Formula Li + and N 3- a 2+ and l - Na + and S 2- Al 3+ and Br - Problem 3 Use the ions of the pairs of elements below to give the formula for their ionic compound. a. Ba and O b. Al and S c. K and P 5

6 Names of ommon Ions Memorize: Their Structure, harge and Name (see the handout on common ions). Look for patterns. Polyatomic Ions 2.8 Naming ompounds 1. lassify the compound: a) Ionic metal and nonmetal (contains ions). b) Acid formula begins with. c) Binary molecular two nonmetals. d) Organic contains,, possibly O, N (carbon based). 2. Use appropriate rules to name the compound. Naming Ionic ompounds a. Write the name of the cation. (Name of the element). b. If the anion is an element, change its ending to -ide; if the anion is a polyatomic ion, simply write the name of the polyatomic ion. c. If the cation can have more than one possible charge, write the charge as a Roman numeral in parentheses. d. Name the cation, then the anion. (We do not need to specify how many of each there are. Why?) Naming Ionic ompounds ompound ontains Name BaBr2 Ba 2+, Br KO K +,O Snl2 Sn 2+, l Snl4 Sn 4+, l PbO2 Pb 4+, O 2 MgSO4 Mg 2+, SO4 2 Fe3(PO4)2 Fe 2+, PO4 3 FePO4 Fe 3+, PO4 3 (N4)2O3 N4 +, O3 2 6

7 Problem 4 Problem 5 Name: Write the formulas: ai2 alcium hypochlorite K2SO4 (N4)2S uf uf2 Ag2O3 Sodium bicarbonate obalt (III) oxide Lithium phosphate Nickel (II) cyanide Aluminum nitrite r(no3)3 Naming Acids ontain + and an anion, but the formula is neutral overall. a. Binary acids (its anion ends in _ide ) ydro ic acid l ydrochloric acid Br ydrobromic acid 2S ydrosulfuric acid b. Oxyacids (anion ends in _ite or _ate.) The name is related to the name of the anion: If the anion ends in: _ate _ite acid ends in: _ic acid _ous acid NO3 NO3 nitrate nitric acid NO2 NO2 nitrite nitrous acid 2SO4 SO4 2 sulfate sulfuric acid 2SO3 SO3 2 sulfite sulfurous acid 3PO4 PO4 3 phosphate phosphoric acid Problem 6 Name: 23O2 ; I 2O3 ; lo4 7

8 Problem 7 Give the Formula: ydrofluoric acid ; hlorous acid ypochlorous acid ; hromic acid Naming Binary Molecular ompounds Made of two nonmetals, these compounds DO NOT contain ions. ommon names (exceptions): 2O Water N3 Ammonia P3 Phosphine To name Binary Molecular ompounds we use numeral prefixes. Why? - Name the first element. - Second element ends in _ide. - Don t use mono for the first element. Naming Binary Molecular ompounds O2 carbon dioxide O carbon monoxide (just one o ) N2O Pl5 N2O4 dinitrogen monoxide phosphorus pentachloride dinitrogen tetroxide ( a omitted) Naming Binary Molecular ompounds Note: Pure Substance Aqueous Solution l(g) hydrogen chloride hydrochloric acid 2S(g) hydrogen sulfide hydrosulfuric acid Problem 8 Name: Formulas: lf3 ; Phosphorus triiodide P4O10 ; Sulfur dichloride SO3 ; Xenon trioxide 8

9 Problem 9 Name: o(no2)2 ; Pl3 BrO3 ; aso3 N2F4 ; Zn(23O4) 2 F Problem 10 Formulas: Tin (IV) permanganate ; Sulfurous acid Lithium sulfite ; Dioxygen difluoride Silver oxide ; Periodic acid Nickel (II) carbonate 2.9 Organic ompounds Organic chemistry is the study of carbon; it has its own system of nomenclature. There are literally millions of organic compounds, which are divided in families (posses certain structural features that identify them). Alkanes contain and only and no multiple bonds (the simplest hydrocarbons) Methane Ethane Propane The family of alcohols: molecules that contain the O group. We use the ol ending. O O O 3O 25O 37O Methanol Ethanol 1-Propanol 9