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Lecture Presentation Chapter 2 Atoms, Molecules, and Ions John D. Bookstaver St. Charles Community College Cottleville, MO © 2012 Pearson Education, Inc. Atomic Theory of Matter The theory that atoms are the fundamental building blocks of matter reemerged in the early nineteenth century, championed by John Dalton. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Dalton's Postulates Each element is composed of extremely small particles called atoms. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Dalton's Postulates All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Dalton's Postulates Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical Atoms, reactions. Molecules, © 2012 Pearson Education, Inc. and Ions Dalton's Postulates Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms. Atoms, © 2012 Pearson Education, Inc. Molecules, and Ions Law of Conservation of Mass The total mass of substances present at the end of a chemical process is the same as the mass of substances present before the process took place. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions The Electron • Streams of negatively charged particles were found to emanate from cathode tubes, causing fluorescence. • J. J. Thomson is credited with their discovery (1897). © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions The Electron Thomson measured the charge/mass ratio of the electron to be 1.76 108 coulombs/gram (C/g). Atoms, © 2012 Pearson Education, Inc. Molecules, and Ions Millikan Oil-Drop Experiment Once the charge/mass ratio of the electron was known, determination of either the charge or the mass of an electron would yield the other. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Millikan Oil-Drop Experiment Robert Millikan (University of Chicago) determined the charge on the electron in 1909. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Radioactivity • Radioactivity is the spontaneous emission of radiation by an atom. • It was first observed by Henri Becquerel. • Marie and Pierre Curie also studied it. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Radioactivity • Three types of radiation were discovered by Ernest Rutherford: particles particles rays © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions The Atom, circa 1900 • The prevailing theory was that of the “plum pudding” model, put forward by Thomson. • It featured a positive sphere of matter with negative electrons imbedded in it. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Discovery of the Nucleus Ernest Rutherford shot particles at a thin sheet of gold foil and observed the pattern of scatter of the particles. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions The Nuclear Atom Since some particles were deflected at large angles, Thomson’s model could not be correct. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions The Nuclear Atom • Rutherford postulated a very small, dense nucleus with the electrons around the outside of the atom. • Most of the volume of the atom is empty space. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Other Subatomic Particles • Protons were discovered by Rutherford in 1919. • Neutrons were discovered by James Chadwick in 1932. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Subatomic Particles • Protons and electrons are the only particles that have a charge. • Protons and neutrons have essentially the same mass. • The mass of an electron is so small we ignore it. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Symbols of Elements Elements are symbolized by one or two letters. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Symbols of Elements All atoms of the same element have the same number of protons, which is called the atomic number, Z. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Symbols of Elements The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Structure of the Nucleus • Soddy discovered that the same element could have atoms with different masses, which he isotopes called _______ there are 2 isotopes of chlorine found in nature, one that has a mass of about 35 amu and another that weighs about 37 amu • The observed mass is a weighted average of the weights of all the naturally occurring atoms the atomic mass of chlorine is 35.45 amu 24 Isotopes • Isotopes are atoms of the same element with different masses. • Isotopes have different numbers of neutrons. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Isotopes • all isotopes of an element have the same number of protons, but different number of neutrons • isotopes of an element have different masses numbers (A) • isotopes are identified by their mass _______________ protons + neutrons 26 Isotopes • Cl-35 makes up about 75% of chlorine atoms in nature, and Cl-37 makes up the remaining 25% • the average atomic mass of Cl is 35.45 amu • Cl-35 has a mass number = 35, 17 protons and 18 neutrons (35 - 17) 35 17 Cl Atomic Symbol A = mass number Z = atomic number AX Z 27 Atomic Mass Atomic and molecular masses can be measured with great accuracy using a mass spectrometer. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Average Mass • Because in the real world we use large amounts of atoms and molecules, we use average masses in calculations. • Average mass is calculated from the isotopes of an element weighted by their relative abundances. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Periodic Table • The periodic table is a systematic catalog of the elements. • Elements are arranged in order of atomic number. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Periodic Table • The rows on the periodic chart are periods. • Columns are groups. • Elements in the same group have similar chemical properties. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions The Modern Periodic Table • Elements with similar chemical and physical properties are in the same column Families Groups • columns are called _______ or ________ – designated by a number and letter at top Periods • rows are called _______ • Main Group = ‘A’ groups • Transition Elements = ‘B’ groups – all metals • Bottom rows = Inner Transition Elements 32 Atoms, Molecules, and Ions Periodicity When one looks at the chemical properties of elements, one notices a repeating pattern of reactivities. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Groups These five groups are known by their names. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Important Groups – IA, Alkali Metals • hydrogen usually placed here, though it doesn’t belong • soft, low melting points,low density • flame tests Li = red, Na = yellow, K = violet • very reactive, never find uncombined in nature 35 lithium sodium potassium rubidium cesium Atoms, Molecules, and Ions Important Groups – IIA, Alkaline Earth Metals • harder, higher melting, and denser than alkali metals beryllium • flame tests Ca = red, Sr = red, Ba = magnesium yellow-green calcium • reactive, but less strontium than corresponding barium alkali metal 36 Atoms, Molecules, and Ions Important Groups – VIIA, Halogens • nonmetals • F2 & Cl2 gases; Br2 liquid; I2 solid • all diatomic • very reactive fluorine chlorine bromine iodine 37 Atoms, Molecules, and Ions Important Groups – VIIIA, Noble Gases • all gases at room temperature, – very low melting and boiling points • very unreactive, practically inert • very hard to remove electron from or give an electron to 38 Atoms, Molecules, and Ions Periodic Table Nonmetals are on the right side of the periodic table (with the exception of H). © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Nonmetals • poor conductors of heat • poor conductors of electricity • solids are brittle • gain electrons in reactions to become anions • upper right on the table – except H 40 Atoms, Molecules, and Ions Periodic Table Metalloids border the stair-step line (with the exception of Al, Po, and At). © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Metalloids • show some properties of metals and some of nonmetals • also known as semiconductors Properties of Silicon shiny conducts electricity does not conduct heat well brittle 42 Atoms, Molecules, and Ions Periodic Table Metals are on the left side of the chart. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Metals • solids at room temperature, except Hg • reflective surface – shiny • conduct heat • conduct electricity • malleable – can be shaped • ductile – drawn or pulled into wires • lose electrons and form cations in reactions • about 75% of the elements are metals • lower left on the table 44 Atoms, Molecules, and Ions Atomic Structures of Ions • Metals form cations • For each positive charge the ion has 1 less electron than the neutral atom Na atom = 11 p+ and 11 e-, Na+ ion = 11 p+ and 10 e Ca atom = 20 p+ and 20 e-, Ca2+ ion = 20 p+ and 18 e- • Cations are named the same as the metal sodium Na Na+ + 1esodium ion calcium Ca Ca2+ + 2ecalcium ion • The charge on a cation can be determined from the Group number on the Periodic Table Group 1A 1+, Group 2A 2+, (Al, Ga, In) 3+ 45 Atomic Structures of Ions • Nonmetals form anions • For each negative charge the ion has 1 more electron than the neutral atom F = 9 e-, F- = 10 e P = 15 e-, P3- = 18 e- • Anions are named by changing the ending of the name to -ide fluorine F + 1e- Ffluoride ion oxygen O + 2e- O2oxide ion • The charge on an anion can be determined from the Group number on the Periodic Table Group 7A 1–, Group 6A 2– 46 Atomic Structures of Ions + - Ion p e Cl– 17 19 18 18 2– 16 18 2+ 38 36 K+ S Sr 47 Classifying Materials • atomic elements = elements whose particles are single atoms (i.e. Cu) • molecular elements = elements whose particles are multi-atom molecules (i.e. O2) • molecular compounds = compounds whose particles are molecules made of only nonmetals (i.e. CO2) • ionic compounds = compounds whose particles are cations and anions (i.e. NaCl) 48 Molecular Elements • Certain elements occur as 2 atom molecules • Rule of 7’s there are 7 common diatomic elements find the element with atomic number 7, N make a figure 7 by going over to Group 7A, then down don’t forget to include H2 VIIA H2 N2 7 O2 F2 Cl2 Br2 I2 49 Ionic Compounds cation + _________ anion • _______ • no individual molecule units, instead have a 3-dimensional array of cations and anions made of formula units 50 Molecular View of Elements and Compounds 51 Nomenclature Common Names - Exceptions • • • • • water H2O = _______ ammonia NH3 = ___________ CH4 = methane __________ salt NaCl = table __________ sugar C12H22O11 = table ____________ 52 Chemical Formulas The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Chemical Formulas Molecular compounds are composed of molecules and almost always contain only nonmetals. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Diatomic Molecules • These seven elements occur naturally as molecules containing two atoms: – Hydrogen – Nitrogen – Oxygen – Fluorine – Chlorine – Bromine – Iodine © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Types of Formulas • Empirical formulas give the lowest wholenumber ratio of atoms of each element in a compound. • Molecular formulas give the exact number of atoms of each element in a compound. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Types of Formulas • Structural formulas show the order in which atoms are bonded. • Perspective drawings also show the three-dimensional array of atoms in a compound. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Ions • When atoms lose or gain electrons, they become ions. – Cations are positive and are formed by elements on the left side of the periodic chart. – Anions are negative and are formed by elements on the right side of the periodic chart. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Ionic Bonds Ionic compounds (such as NaCl) are generally formed between metals and nonmetals. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Writing Formulas • Because compounds are electrically neutral, one can determine the formula of a compound this way: – The charge on the cation becomes the subscript on the anion. – The charge on the anion becomes the subscript on the cation. – If these subscripts are not in the lowest wholenumber ratio, divide them by the greatest common Atoms, factor. Molecules, © 2012 Pearson Education, Inc. and Ions Common Cations © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Common Anions © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions • Ionic Nomenclature Major Classes metal + nonmetal metal first in formula Binary Ionic compounds with polyatomic ions • Molecular 2 nonmetals Binary Molecular (or Binary Covalent) Acids – formula starts with H though acids are molecular, they behave as ionic when dissolved in water may be binary or oxyacid 63 Metal Cations • Type I metals whose ions can only have one possible charge IA, IIA, (Al, Ga, In) determine charge by position on the Periodic Table IA = 1+, IIA = 2+, (Al, Ga, In = 3+) • Type II metals whose ions can have more than one possible charge mostly transition metals 64 Type I Binary Ionic Compounds • Contain Metal Cation + Nonmetal Anion • Metal listed first in formula & name 1. name metal cation first, name nonmetal anion second 2. cation name is the metal name 3. nonmetal anion named by changing the ending on the nonmetal name to -ide 65 Type II Binary Ionic Compounds • • Contain Metal Cation + Nonmetal Anion Metal listed first in formula & name 1. name metal cation first, name nonmetal anion second 2. metal cation name is the metal name followed by a Roman Numeral in parentheses to indicate its charge 3. nonmetal anion named by changing the ending on the nonmetal name to -ide 66 Examples • • • • • • • lithium chloride LiCl = _________________ chloride AlCl3 = aluminum ____________________ oxide PbO = lead(II) ______________ oxide PbO2 = lead(IV) _______________ manganese(III) oxide Mn2O3 = _______________________ zinc chloride ZnCl2 = ______________ chloride AgCl = silver _______________ 67 Example – Name the following compounds: Na2SO4 sodium sulfate Fe(NO3)3 iron(III) nitrate 68 Binary Molecular Compounds of 2 Nonmetals 1. Name first element in formula first use the full name of the element 2. Name the second element in the formula with an -ide as if it were an anion, however, remember these compounds do not contain ions! 3. Use a prefix in front of each name to indicate the number of atoms a) Do not use the prefix mono- on the first element 69 Subscript - Prefixes mono• 1 = ________; not used on first nonmetal • • • • • • • • • • 2 = di_______ 3 = tri_______ 4 = tetra_______ Example – Name the 5 = penta_______ following compound: 6 = hexa_______ boron trifluoride BF 3 7 = hepta_______ 8 = octa_______ 9 = nona_______ 10 = deca_______ 70 drop last “a or o” if name begins with vowel Acids • Contain H+ cation in aqueous solution • Binary acids have H+ cation and nonmetal anion • Oxyacids have H+ cation and polyatomic anion containing oxygen 71 Acids • acids are molecular compounds that often behave like they are made of ions • All names have acid at end • Binary Acids = hydro prefix + stem of the name of the nonmetal + ic suffix 72 • Oxyacids Acids if polyatomic ion ends in –ate = name of polyatomic ion with –ic suffix if polyatomic ion ends in –ite = name of polyatomic ion with –ous suffix 73 Example – Name the following compounds: HCl hydrochloric acid H2SO4 sulfuric acid H2SO3 sulfurous acid 74 Inorganic Nomenclature • Write the name of the cation. • 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. • If the cation can have more than one possible charge, write the charge as a Roman numeral in parentheses. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Patterns in Oxyanion Nomenclature • When there are two oxyanions involving the same element: – The one with fewer oxygens ends in -ite. – The one with more oxygens ends in -ate. • NO2− : nitrite; SO32− : sulfite • NO3− : nitrate; SO42− : sulfate © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Patterns in Oxyanion Nomenclature • Central atoms on the second row have bond to at most three oxygens; those on the third row take up to four. • Charges increase as you go from right to left. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Patterns in Oxyanion Nomenclature • The one with the second fewest oxygens ends in -ite. – ClO2− : chlorite • The one with the second most oxygens ends in -ate. – ClO3− : chlorate © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Patterns in Oxyanion Nomenclature • The one with the fewest oxygens has the prefix hypo- and ends in -ite. – ClO− : hypochlorite • The one with the most oxygens has the prefix per- and ends in -ate. – ClO4− : perchlorate © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Acid Nomenclature • If the anion in the acid ends in -ide, change the ending to -ic acid and add the prefix hydro- . – HCl: hydrochloric acid – HBr: hydrobromic acid – HI: hydroiodic acid © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Acid Nomenclature • If the anion in the acid ends in -ite, change the ending to -ous acid. – HClO: hypochlorous acid – HClO2: chlorous acid © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Acid Nomenclature • If the anion in the acid ends in -ate, change the ending to -ic acid. – HClO3: chloric acid – HClO4: perchloric acid © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Nomenclature of Binary Compounds • The less electronegative atom is usually listed first. • A prefix is used to denote the number of atoms of each element in the compound (mono- is not used on the first element listed, however) . © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Nomenclature of Binary Compounds • The ending on the more electronegative element is changed to -ide. – CO2: carbon dioxide – CCl4: carbon tetrachloride © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Nomenclature of Binary Compounds • If the prefix ends with a or o and the name of the element begins with a vowel, the two successive vowels are often elided into one. N2O5: dinitrogen pentoxide © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Nomenclature of Organic Compounds • Organic chemistry is the study of carbon. • Organic chemistry has its own system of nomenclature. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Nomenclature of Organic Compounds The simplest hydrocarbons (compounds containing only carbon and hydrogen) are alkanes. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Nomenclature of Organic Compounds The first part of the names just listed correspond to the number of carbons (meth- = 1, eth- = 2, prop- = 3, etc.). © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions Nomenclature of Organic Compounds • When a hydrogen in an alkane is replaced with something else (a functional group, like -OH in the compounds above), the name is derived from the name of the alkane. • The ending denotes the type of compound. – An alcohol ends in -ol. © 2012 Pearson Education, Inc. Atoms, Molecules, and Ions