che106_lecture5 - Chemistry 106 Lecture 5 Topics ...

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Unformatted text preview: Chemistry 106 Lecture 5 Topics: Periodic Table Molecules, Ions, Compounds Chapter 2.5 – 2.8 Announcements Ø།  Reminder: Second Homework and Tutorial sets are due on the MasteringChemistry website on Friday, September 16. The Periodic Table •  In 1869, Dmitri Mendeleev discovered that if the known elements were arranged in order of atomic number, they could be placed in horizontal rows such that the elements in the ver/cal columns had similar properOes. The Periodic Table Periodicity When one looks at the chemical properOes of elements, one noOces a repeaOng paQern of reacOviOes. Periods and Groups •  The periodic table is a tabular arrangement of elements in rows and columns, highlighOng the regular repeOOon of properOes of the elements. –  A period consists of the elements in one horizontal row of the periodic table. –  A group consists of the elements in any one column of the periodic table. –  The groups are usually numbered. –  The eight “A” groups are called main group (or representaOve) elements. The Periodic Table Groups run vertical (columns) Periods run horizontal (rows) The Periodic Table •  Periods and Groups –  The “B” groups are called transi/on elements. –  The two rows of elements at the boQom of the table are called inner transi/on elements. –  Elements in any one group have similar properOes. The Periodic Table The “halogens” all have similar properties TransiOon Elements Inner TransiOon Elements The Periodic Table •  Periods and Groups –  The elements in group 1A, oZen known as the alkali metals, are soZ metals that react easily with water. –  The group 7A elements, known as the halogens, are also reacOve elements. –  The group 8A elements, known as the noble gases, generally are non- reac/ve. Table 2.3 Metals, Nonmetals, and Metalloids •  A metal is an element that has a luster (shine), a good conductor of heat and electricity, and oZen malleable and duc)le. Copper and gold are examples. •  A nonmetal is an element that does not exhibit the characterisOcs of the metal. Carbon and oxygen are examples. •  A metalloid, or semi- metal, is an element having both metallic and nonmetallic properOes. Silicon and germanium are good semiconductors. The Periodic Table Tying it all Together: Chemical Formulas •  The chemical formula of a substance is a notaOon using atomic symbols with subscripts to convey the relaOve proporOons of atoms of the different elements in a substance. •  Consider the formula of aluminum oxide, Al2O3. This formula indicates that the compound is composed of aluminum atoms and oxygen atoms in the raOo 2:3. Molecular Substances •  A molecule is a definite group of atoms that are chemically bonded together – that is, Oghtly connected by aQracOve forces. •  A molecular substance is a substance that is composed of molecules, all of which are alike. •  A molecular formula gives the exact number of atoms of elements in a molecule. •  Structural formulas show how the atoms are bonded to one another in a molecule. Molecular and Structural Formulas and Molecular Models Molecular vs. Empirical Formulas •  Molecular formulas give the exact number of atoms of each element in a compound. C6H6 •  Empirical formulas give the lowest whole- number raOo of atoms of each element in a compound. C6H6 C1H1 Molecular Formula Examples Write the molecular formula of each of these compounds. H2O4S or H2SO4 C6H6 Benzene C3H6O Element Ordering in Molecular Formulas The basic method for determining the order in which elements are listed in a molecular formula is covered by two rules: 1.  The number of carbon atoms is listed first, the number of hydrogen atoms listed second, the number of all other elements are then listed in alphabeOcal order. C3H6O 2.  If there is no carbon in the molecule, then just list all the elements alphabeOcally (even hydrogen). Element Ordering in Molecular Formulas Ordering of elements in a formula may also be done by lisOng the most metallic element first, followed by the less metallic. Organic and Inorganic Compounds •  Chemical compounds are classified as organic or inorganic. •  Organic compounds are compounds that contain carbon combined with other elements, such as hydrogen, oxygen, and nitrogen. •  Inorganic compounds are compounds composed of elements other than carbon. Organic Compounds •  Organic compounds (carbon containing) are an important class of molecular substances. •  Organic compounds make up the majority of all known compounds. •  The simplest organic compounds are hydrocarbons, or compounds containing only hydrogen and carbon. •  Common examples include methane, CH4, ethane, C2H6, and propane, C3H8. (Part of the alkane family.) Some Simple Hydrocarbons Methane Ethane Propane The hydrocarbons above do not smell, so ethanethiol is added to them so that leaks can be detected. Ionic Substances •  Although many substances are molecular, others are composed of ions. •  An ion is an electrically charged parOcle obtained from an atom or chemically bonded group of atoms by adding or removing electrons. •  Sodium chloride is a substance made up of ions. Ionic Substance Example A ball- and- sOck model of a porOon of a sodium chloride (NaCl) crystal. A Space- Filling Model HighlighOng the Packing Arrangement of the Sodium and Chloride Ions in a Solid Sodium Chloride Crystal Photograph Showing Crystals of Sodium Chloride The cubic shape of the packing arrangement of the Na+ and Cl- ions is preserved at the macroscopic scale. Source: ©E.R. Degginger Ionic Substances •  When an atom picks up extra electrons, it becomes a nega)vely charged ion, called an anion. •  An atom that loses electrons becomes a posi)vely charged ion, called a ca/on. •  An ionic compound is a compound composed of caOons and anions. Ionic Substances: NaCl CaOon Anion Ionic Substances •  The formula of an ionic compound is wriQen by giving the smallest possible whole- number raOo of different ions in the substance. •  The formula unit of the substance is the group of atoms or ions explicitly symbolized by its formula. WriOng Ionic Formulas 3 x +2 = +6 +6 + - 6 = 0 2 x - 3 = - 6 •  Because compounds are electrically neutral (charges add up to zero), one can determine the formula of a compound this way: –  The charge on the caOon becomes the subscript on the anion. –  The charge on the anion becomes the subscript on the caOon. –  If these subscripts are not in the lowest whole- number raOo, divide them by the greatest common factor. Ionic compounds •  Most ionic compounds contain metal and nonmetal atoms; for example, NaCl. •  You name an ionic compound by giving the name of the ca/on followed by the name of the anion. Metal Nonmetal Which CombinaOon is Likely to Produce an Ionic Compound? A.  C and H B.  S and Cl C.  Ca and F D.  Br and I E.  Xe and F Which CombinaOon is Likely to Produce an Ionic Compound? A.  C and H B.  S and Cl C.  Ca and F D.  Br and I E.  Xe and F Monatomic Ions •  When atoms lose or gain electrons, they become ions. •  A monatomic ion is formed from a single atom. –  Ca/ons are posiOve and are formed by elements on the le6 side of the periodic chart. –  Anions are negaOve and are formed by elements on the right side of the periodic chart. Rules for PredicOng Charges on Monatomic Ions •  Most of the main group metals form ca)ons with the charge equal to their group number. –  Na is in Group 1A and has +1 charge. –  Mg is in Group 2A and has a +2 charge. •  The charge on a monatomic anion for a nonmetal equals the group number minus 8. –  O is in Group 6B and has a - 2 charge. –  F is in Group 7B and has a - 1 charge. •  Most transi/on elements form more than one ion, each with a different charge. TransiOon Element CaOons The transiOon element ions are someOmes difficult to idenOfy without addiOonal informaOon since there are oZen mulOple ions that may exist. Rules for Naming Monatomic Ions •  Monatomic caOons are named aZer the element. For example, Al3+ is called the aluminum ion. •  If there is more than one caOon of an element, a Roman numeral in parentheses denoOng the charge on the ion is used. This oZen occurs with transiOon elements. Such as Iron(II) and Iron(III). •  The names of the monatomic anions use the stem name of the element followed by the suffix –ide. For example, Br- is called the bromide ion. Table 2.4 Common CaOons Table 2.5 Common Anions Inorganic/Ionic Nomenclature (Naming) •  Write the name of the caOon. •  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 caOon can have more than one possible charge, write the charge as a Roman numeral in parentheses. Naming Binary Ionic Compounds •  NaF – Sodium Fluoride •  LiCl – Lithium Chloride •  MgO – Magnesium Oxide •  FeO – Iron(II) Oxide Polyatomic Ions •  A polyatomic ion is an ion consisOng of two or more atoms chemically bonded together and carrying a net electric charge. − NO 3 nitrate − NO 2 nitrite SO 4 2− sulfate SO 3 2− sulfite Common Polyatomic Ions Naming and Polyatomic Ions Na2SO4 Sodium Sulfate AgCN Silver Cyanide Ca(ClO)2 Calcium Hypochlorite Na2SO3 Sodium Sulfite Cd(OH)2 Cadmium Hydroxide KClO4 Potassium Perchlorate PaQerns in Oxyanion Nomenclature •  When there are two oxyanions (anions containing oxygen) involving the same element: –  The one with fewer oxygens ends in - ite. •  NO2− : nitrite; SO32− : sulfite –  The one with more oxygens ends in - ate. •  NO3− : nitrate; SO42− : sulfate PaQerns in Oxyanion Nomenclature What about more complicated oxyanions? How are they named? •  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 PaQerns in Oxyanion Nomenclature What about intermediate oxygen counts? How are they named? •  The one with the second fewest oxygens ends in - ite. – ClO2− : chlorite •  The one with the second most oxygens ends in - ate. – ClO3− : chlorate Which is the correct name for NaOCl, the acOve ingredient in Clorox bleach? a.  sodium chlorate b.  sodium chlorite c.  sodium perchlorate d.  sodium hypochlorite Which is the correct name for NaOCl, the acOve ingredient in Clorox bleach? a.  sodium chlorate b.  sodium chlorite c.  sodium perchlorate d.  sodium hypochlorite Binary Molecular Compounds •  A binary compound is a compound composed of only two elements. •  Binary compounds composed of a metal and a non- metal are usually ionic and are named as ionic compounds. •  Binary compounds composed of two nonmetals are usually molecular and are named using a prefix system. Binary Molecular Compounds •  The name of the compound has the elements in the order given in the formula. •  You name the first element using the exact element name. •  Name the second element by wriOng the stem name of the element with the suffix “–ide.” •  If there is more than one atom of any given element, you add a prefix. Table 2.6 lists the Greek prefixes used. Binary Molecular Compounds •  Here are some examples of prefix names for binary molecular compounds. –  SF4 sulfur tetrafluoride –  ClO2 chlorine dioxide –  SF6 s ulfur hexafluoride –  Cl2O7 dichlorine heptoxide Two successive vowels are oZen combined. Binary Molecular Compounds Nitrogen trifluoride Oxygen difluoride Diphosphorous tetrahydride #1) The more metallic element comes first in names. #2) If the elements are in the same group, place the higher atomic number first. Acids •  Acids are tradiOonally defined as compounds that yield a H+ caOon and some anion when dissolved in water. •  Binary acids consist of a hydrogen ion and any single anion. For example, HCl is hydrochloric acid (H+ and Cl- in water soluOon). •  An oxoacid is an acid containing hydrogen, oxygen, and another element. An example is HNO3, nitric acid (H+ and NO3- in water soluOon). 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 Acid Nomenclature •  If the anion in the acid ends in - ate, change the ending to - ic acid. –  HClO3: chloric acid –  HClO4: perchloric acid Acid Nomenclature •  If the anion in the acid ends in - ite, change the ending to - ous acid. –  HClO: hypochlorous acid –  HClO2: chlorous acid Oxoanions and Oxoacids Next Lecture •  Topics: ReacOons and Stoichiometry •  Text Reading: 3.1 - 3.2 ...
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This note was uploaded on 10/04/2011 for the course CHE 106 taught by Professor Freedman during the Fall '08 term at Syracuse.

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