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Chapter 2 (Essentials of General Chemistry, 2nd Edition) (Ebbing and Gammon) Atoms, Molecules and Ions Atomic Theory of Matter John Dalton (British Chemist) - basic theory of modern chemistry - all matter whether element, compound or mixture is composed of small particles called atoms - purpose of atomic theory: to provide explanation of the structure of matter in terms of different combinations of very small particles Karen Hattenhauer (Fall 2007) 2 Postulates of Dalton s Atomic Theory 1.) All matter is composed of indivisible atoms. An atom is an extremely small particle of matter that retains its identity during chemical reactions. 2.) An element is a type of matter composed of only one kind of atom, each atom of a given kind having the same properties. 3.) A compound is a type of matter composed of atoms of two or more elements chemically combined in fixed proportions. 4.) A chemical reaction consists of the rearrangement of the atoms present in the reacting substances to give new chemical combinations present in the substances formed by the reaction. Karen Hattenhauer (Fall 2007) 3 1 Atomic Symbols and Models Atomic symbol - a one- or two-letter notation used to represent an atom corresponding to a particular element - convention: first letter capital second letter lowercase - origin: from the name of the element from a name in another language (Latin) Atomic Models - Dalton used spheres to represent atoms and used combinations of these spheres to represent compounds - still used today but more refined Karen Hattenhauer (Fall 2007) 4 Representations of Molecules Karen Hattenhauer (Fall 2007) 5 Deductions from Dalton s Atomic Theory Explains: 1.) difference between element and compound 2.) Law of Mass Conservation - states that total mass remains constant during a chemical reaction 3.) Law of Definite Proportions - compound is type of matter containing atoms of two or more elements is definite proportions 4.) Law of Multiple Proportions - when two elements form more than one compound, the masses of one element in these compounds for a fixed mass of the other element are in rations of small whole numbers Karen Hattenhauer (Fall 2007) 6 2 The Structure of the Atom Two Particles: 1.) nucleus (atom s central core) - positively charged - contains most of atoms mass 2.) electron (outside atom s central core) - negatively charged - very light Karen Hattenhauer (Fall 2007) 7 Discovery of the Electron Cathode-ray Tube (J. J. Thomson- 1897) - used experimental apparatus to conclude that cathode ray consists of beam of negatively charged particles (or electrons) charge-to-mass ratio calculation (e/m) - ratio of e- electric charge to its mass modern (excepted value): e/m = 1.758820 x 108 C/g e = magnitude of charge of e- in coulombs (C) m = mass of e- in grams Karen Hattenhauer (Fall 2007) 8 A Cathode-ray Tube Karen Hattenhauer (Fall 2007) 9 3 Measuring the Mass of an Electron Oil-drop Experiment (Robert A. Millikan 1909) - experiment used to obtain the charge on an electron (1.602 x 10-19 coulombs) - using charge-to-mass ratio (by Thomson) e = 1.758820 x 108 C/g m then m= e = 1.602176 x 10-19 C 8 1.758820 x 10 g/C 1.758820 x 108 C/g = 9.109382 x 10-28 g Karen Hattenhauer (Fall 2007) 10 Millikan s Oil-drop Experiment Karen Hattenhauer (Fall 2007) 11 Nuclear Model of Atom Ernest Rutherford (British Physicist - 1911) - proposed that metal atom he was studying must be almost entirely empty space with mass concentrated in tiny central core - showed that atoms consisted of a positively charged nucleus at the center of the atom, around which negatively charged electrons move - nucleus occupies only very small portion of space of atom nuclei diameters 10-3 picometers atomic diameters 100 picometers Karen Hattenhauer (Fall 2007) 12 4 The Rutherford Scattering Experiment Karen Hattenhauer (Fall 2007) 13 Nuclear Structure: Isotopes Structure of Nucleus: 1.) proton -a nuclear particle having a positive charge equal to that of the electron and has a mass more than 1800 times that of the electron 2.) neutron - a nuclear particle having a mass almost identical to that of the proton but no electric charge Note: characterize nucleus by atomic number (Z) and mass number (A) Karen Hattenhauer (Fall 2007) 14 Atomic Composition atomic number (Z) - number of protons in nucleus of an atom - charge of nucleus of particular atom is equal to number of protons element substance whose atoms all have the same atomic number atomic number (Z) = number of protons mass number (A) - total number of protons and neutrons in a nucleus A = number of protons + number of neutrons Karen Hattenhauer (Fall 2007) 15 5 Atomic Composition: Nuclear Symbol nuclide atom characterized by a definite atomic number and mass number atomic no. - subscript at lower left of the element symbol mass no. - superscript at upper left of the element symbol A X Z where: X = element symbol A = mass number Z = atomic number isotopes atoms whose nuclei have the same atomic number but different mass numbers (ie. nuclei have the same number of protons but different numbers of neutrons) Karen Hattenhauer (Fall 2007) 16 Atomic Mass Units mass spectrometer - instrument to measure relative atomic masses atomic mass unit (amu) - convenient unit used for reporting mass of atoms - mass of atom is compared to a carbon-12 isotope which is assigned a mass of exactly 12 atomic mass units (amu) - therefore, 1 amu = 1/12 mass of a carbon-12 atom atomic mass (of an element) - the average atomic mass for the naturally occurring element, expressed in atomic mass units Karen Hattenhauer (Fall 2007) 17 Diagram of a Simple Mass Spectrometer Figure 2.8: Showing the Separation of Neon Isotopes Karen Hattenhauer (Fall 2007) 18 6 Periodic Table of the Elements Dmitri Mendeleev and J. Lothar Meyer - tabular arrangement of elements in rows and columns, highlighting the regular repetition of properties of the elements - today arrangement of elements by atomic number (represents element by symbol, atomic number and atomic mass) Organization of the periodic table A.) i.) periods consists of elements in any one horizontal row of periodic table ii.) groups consists of elements in any one column of periodic table Karen Hattenhauer (Fall 2007) 19 A modern form of the periodic table Figure 2.11 Karen Hattenhauer (Fall 2007) 20 Numbers and Labels Two systems: 1.) labels the groups with Roman numerals and A s and B s i.) North America (IA) ii.) Europe (AI) Categories within periodic table: - main-group elements: A groups - transition elements: B groups - inner-transition elements: lanthanides (1st row) actinides (2nd row) 2.) International Union of Pure and Applied Chemistry (IUPAC) has convention with columns numbered 1 to 18 Karen Hattenhauer (Fall 2007) 21 7 Similarity in Chemical Properties Group 1A (Alkali metals) - shiny and soft - react violently with H2O - not found in nature in pure form (highly reactive) - exception - hydrogen Group 7A (Halogens) -colorful, corrosive nonmetals - found in nature only in combination with other elements Karen Hattenhauer (Fall 2007) 22 Metals, Nonmetals and Metalloids Categories: i.) metals - substance or mixture that has a characteristic luster (ie. silvery shine) - all solid at R.T. (except mercury (Hg)) - generally malleable and ductile rather than brittle (easily shaped) - good conductors of heat and electricity Karen Hattenhauer (Fall 2007) 23 ii.) nonmetals - element that does nor exhibit the characteristic of a metal - eleven gases, one liquid (Br), five solids (C, P, S, Se, I) - many are brightly colored but none are silvery - solids are hard and brittle rather than malleable - poor conductors of heat and electricity Karen Hattenhauer (Fall 2007) 24 8 iii.) semimetal (metalloid) - border staircase line in periodic table (seven of nine elements adjacent to boundary between metals and nonmetals and include B, Si, Ge, As, Sb, Te, At) - properties intermediate btw metals and nonmetals - semiconductors (eg. silicon and germanium) Karen Hattenhauer (Fall 2007) 25 Chemical Formulas Molecular and Ionic Substances: chemical formula - notation that uses atomic symbols with numerical subscripts to convey the relative proportions of atoms of the different elements in the substance - no subscript - the number 1 is understood Karen Hattenhauer (Fall 2007) 26 Molecular Substances molecule definite group of atoms that are chemically bonded together molecule substance substance composed of molecules that are all alike molecular formula gives exact number of different atoms of an element in a molecule structural formula chemical formula that shows how atoms are bonded to one another - sometimes condensed in writing Karen Hattenhauer (Fall 2007) 27 9 molecular models - atoms in molecule mot only connected in definite ways but exhibit spatial arrangements as well - ball-and-stick and space-filling models Note: - some elements have simple formulas - some elements consist of very large, indefinite number of atoms bonded together Karen Hattenhauer (Fall 2007) 28 Molecular and Structural Formulas and Molecular Models Figure 2.12 Karen Hattenhauer (Fall 2007) 29 Class of Molecular Substances monomers small molecules that are linked together to form polymers polymers - very large molecules that are made up of a number of smaller molecules repeatedly linked i.) natural wool and silk ii.) synthetic Nylon, Kevlar, Nomex, Teflon - plastics and rubbers Karen Hattenhauer (Fall 2007) 30 10 Organic Compounds - class of molecular substances that contain carbon combined with other elements, such as hydrogen, oxygen and nitrogen hydrocarbon - simplest organic compounds - those compounds containing only hydrogen and carbon - extensively used as sources of energy - starting materials for plastics functional group - reactive portion of a molecule that undergoes predictable reactions - determines chemistry of organic molecules inorganic compounds - composed of elements other than carbon Karen Hattenhauer (Fall 2007) 31 Some Organic Functional Groups Karen Hattenhauer (Fall 2007) 32 Ionic Substances ion an electrically charged particle obtained from an atom or molecule by adding or removing electrons i.) anion negatively charged ion - atom that picks up extra electron(s) - nonmetals tend to gain electron(s) ii.) cation positively charged ion - atom that loses electron(s) - metal atoms tend to lose electron(s) Note: ions may consist of two or more atoms chemically bonded but having an excess or deficiency of electron(s) Karen Hattenhauer (Fall 2007) 33 11 Ionic Compounds ionic compound compound composed of cations and anions - held together by strong attraction between positive (+ve) and negative (-ve) charges - always written by giving smallest possible integer number of different ions in a substance formula unit the group of atoms or ions explicitly symbolized in formula Karen Hattenhauer (Fall 2007) 34 Naming Simple Compounds chemical nomenclature - systematic naming of chemical compounds Ionic Compounds - substances composed of ions - positive ion name (metal) is given first followed by the name of the negative ion (nonmetal) Types of ions: i.) monatomic ion - an ion formed from a single atom ii.) polyatomic ion - an ion consisting of two or more atoms chemically bonded together and carrying a net electric charge Karen Hattenhauer (Fall 2007) 35 Monatomic Ions Predicting the Charges of Monatomic Ions 1.) Most of the main-group metallic elements have one monatomic cation with a charge equal to the group number in the periodic table (the Roman numeral) 2.) Some metallic elements have more than one cation. These elements have common cations with a charge equal to the group number minus 2, in addition to having a cation with a charge equal to the group number. 3.) Most transition elements form more than one cation. Most of these elements have one ion with a charge of +2. 4.) The charge on a monatomic anion for a nonmetallic main group element equals the group number minus 8. Karen Hattenhauer (Fall 2007) 36 12 Main-group cations and anions Common transition metals ions Karen Hattenhauer (Fall 2007) 37 Naming Monatomic Ions 1.) Monatomic cations are names after the element. If there is more than one monatomic cation of an element, a Roman numeral in parentheses is used to denote the charge on the ion. 2.) The names of monatomic anions are obtained from a stem name of the element followed by the suffix ide. Table 2.5 Karen Hattenhauer (Fall 2007) 38 Polyatomic Ions cations mercury (I) cation and ammonium cation anions i.) oxoanions (oxyanions) - consist of oxygen with another element -named with stem name from nonmetal element and a.) for element that forms two oxoanions - suffix -ate - oxoanion with greater no. of O - suffix -ite - oxoanion with fewer no. of O b.) for element that forms more than two oxoanions - prefix per- - oxoanion with largest no. of O - prefix hypo- -oxoanion with fewest no. of O Karen Hattenhauer (Fall 2007) 39 13 ii.) acid anions - oxoanions bonded to one or more hydrogen ions (H+) iii.) thiosulfate ion - root ion SO42- (sulfate); thio- means an oxygen atom has been replaced by a sulfur Karen Hattenhauer (Fall 2007) 40 Common Polyatomic Ions Table 2.6 Table 2.6 Karen Hattenhauer (Fall 2007) 41 Binary Molecular Compounds Binary compound compound composed of only two elements i.) ionic compound composed of metal and nonmetal ii.) binary molecular compound two nonmetals or metalloids named using prefix system - usually named using the order given in formula (nonmetals and metals approximately in order of increasing nonmetallic character) a.) 1st element more metallic b.) 2nd element more nonmetallic Karen Hattenhauer (Fall 2007) 42 14 Naming Binary Molecular Compounds 1.) Name of compound usually has elements in order given in formula. 2.) Name the first element using the exact element name. 3.) Name the second element by writing the stem name of the element with the suffix ide. 4.) Add prefix, derived from the Greek, to each element name to denote subscript of element in formula. Note: generally, prefix mono- is not used, unless needed to distinguish two compounds of the same two elements Karen Hattenhauer (Fall 2007) 43 Greek Prefixes Table 2.7 Karen Hattenhauer (Fall 2007) 44 Acids and Anions acid molecular compound that yields hydrogen ions, H+, and an anion for each acid molecule when the acid dissolves in water oxoacids - acid containing hydrogen, oxygen and another element - when dissolved in water, an oxoacid yields one or more H+ ions and polyatomic oxoanions - named as related to oxoanions: i.) -ate suffix replaced by -ic acid ii.) -ite suffix replaced by -ous acid iii.) per- and hypo- prefixes are retained Karen Hattenhauer (Fall 2007) 45 15 Oxoanions and Oxoacids Table 2.8 Table 2.8 46 Karen Hattenhauer (Fall 2007) Binary Molecular Compounds - binary compounds of hydrogen and nonmetals yield acidic solutions when dissolved in water - name these solutions using the prefix hydro- and suffix ic with the stem name of the nonmetal, followed by the word acid - denote solution by formula of binary compound compound followed by (aq) aqueous (water ) solution HCl(g) dissolves in water HCl (aq) (H+, Cl-) hydrogen chloride HBr(g) hydrochloric acid dissolves in water HBr (aq) (H+, Br-) hydrogen bromide hydrobromic acid Karen Hattenhauer (Fall 2007) 47 Hydrates - compound that contains water molecules weakly bound in its crystal - named from the anhydrous compound followed by the word hydrate with a prefix to indicate the number of water molecules per formula unit of the compound eg. CuSO4·5H2O copper (II) sulfate pentahydrate - anhydrous substance in copper (II) sulfate Karen Hattenhauer (Fall 2007) 48 16 Writing Chemical Equations chemical equation symbolic representation of a chemical reaction in terms of chemical formulas i.) reactants formulas on left side of equation ii.) products formulas on right side of equation iii.) arrow reacts to form or yields coefficients number in front of formula give relative number of formula units involved in reaction (Note: coefficient of 1 is understood, not written) states or phases of substances indicated using labels (g) gas, (l) liquid, (s) solid, (aq) - aqueous Karen Hattenhauer (Fall 2007) 49 Symbols over the reaction arrow: i.) if reactants are heated to make a reaction go, place the Greek symbol delta ( ) over the arrow 2 NaNO3 (s) 2 NaNO2 (s) + O2 (g) ii.) catalyst a substance that speeds up a reaction without undergoing any net change itself - the element symbol of the catalytic substance is often placed over the arrow 2 H2O2 (aq) Pt 2 H2O (l) + O2 (g) Karen Hattenhauer (Fall 2007) 50 Balancing Chemical Equations balanced numbers of atoms of each element are equal on both sides of the arrow (this is achieved when coefficients in chemical equation are given correctly) chemical reaction recombination of atoms; none are destroyed and none are created Note: 1.) write the coefficients so that they are the smallest whole numbers possible 2.) balance first the atoms for elements that occur in only one substance on each side of the equation Karen Hattenhauer (Fall 2007) 51 17 This document was created with Win2PDF available at http://www.daneprairie.com. 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