06 Chemical Bonding.pdf

Chemical Bonding  Lewis Theory Chemical Octet Rule Bonding Types of Bonding Outline Formula Chemical Writing Nomenclature Naming Compounds...

Chemical Bonding  Lewis Theory Chemical Octet Rule Bonding Types of Bonding Outline Formula Chemical Writing Nomenclature Naming Compounds Lewis Theory The Lewis Theory Valence electrons refers to a description of chemical bonding through Lewis symbols and Lewis Transfer and sharing of electrons structures in (Ionic and Covalent) accordance with a particular set of rules. Octet Lewis Theory 1. Outermost (valence) electrons, play a fundamental role in chemical bonding. Lewis Theory 2. Electrons are: a. transferred from one atom to another where positive and negative ions are formed and attract each other through electrostatic forces called ionic bonds. b. shared between atoms and these bonds are called covalent bonds. Lewis Theory 3. Electrons are transferred or shared in such a way that each atom acquires an especially stable electron configuration. Usually this is a noble gas configuration, one with eight outer-shell electrons, or an octet. Octet Rule Octet Rule – in forming bonds, main group elements gain, lose, or share electrons to achieve a stable electron configuration with eight valence electrons s2p6 → 8 electrons Same electronic configuration as a noble gas (closed shell configuration) Ex: for Ne, shell 2 is full (2s2 2p6) and shell 3 is empty, all electrons paired. Open shells, which has unpaired electrons, are less stable than closed shells. Types of Bonding Ionic bonding – electron transfer Covalent bonding – electron sharing Metallic bonding – electron pooling  Metallic bonds are an idealized type of bonding based on the attraction between metal ions and a delocalized “sea” of their valence electron. Ex: Na, Mg, Al Types of In general, metal atoms are relatively large and have a small number of outer electrons Bonding that are shielded from the nuclear charge by filled inner levels. Metals lose electrons easily (low IE) but do not gain them easily (small or positive EA) Electrons are delocalized and move freely throughout the piece of metal.  Ionic bonds exist between atoms that have high EN difference Ex: NaCl, ENs are 0.93 and 3.16, respectively Types of Na will tend to give one electron and Cl will accept the electron Bonding Na will become Na+, Cl will become Cl- They will both follow a noble gas configuration Na+ = [Ne] and Cl- = [Ar] Ionic Bond Ionic bonds exist between atoms that have high EN difference Ions are electrically charged atom or group of atoms Atoms that lose electron(s) and become positively charged are cations Cations are smaller than parent atom Atoms that gain electron(s) and become negatively charged are anions Anions are larger than parent atom Ionic Bond Binary ionic compound – composed of just two elements Typically forms when metals react with nonmetals Metal becomes cation, nonmetal becomes anion All binary ionic compounds are solids at standard state Monatomic ion – cation or anion derived from a single atom Polyatomic ion – cation or anion derived from a small group of atoms Ionic compounds are neutral (no net charge).  Covalent bonds exist between atoms with high EN values Ex: Cl2, CCl4 Types of Usually occurs between nonmetals Bonding Bond pair – pair of electrons in covalent bond Lone pair – pair of electrons not involved in bond formation  Covalent Bond Covalent bonds exist between atoms with high EN values Single covalent bond – sharing of a single pair of electrons Ex: Cl2, CCl4 Double covalent bond – sharing of two pairs of electrons Ex: O2, CO2 Triple covalent bond – sharing of three pairs of electrons Ex: N2, CO Coordinate/Dative covalent bond – sharing of a pair of electrons coming from the same atom Ex: NH4+, H3NBF3 Covalent vs Ionic Most covalent substances consist of molecules. Ex: water: H2O molecules are next to each other Under ordinary conditions, no molecules exist in a sample of an ionic compound. Ex: table salt: continuous array of oppositely charged Na+ and Cl- ions, not a collection of NaCl molecules. Polyatomic Ions Polyatomic ions – consist of two or more atoms bonded covalently and have a net positive or negative charge. Ex: calcium carbonate: Ca2+ and CO32- Chemical Nomenclature Types of Chemical Formulas 1. Empirical 2. Molecular 3. Structural Chemical Nomenclature Empirical formula – shows the relative number of atoms of each element in the compound Simplest type of formula derived from the masses of the component elements Ex: hydrogen peroxide: HO Chemical Nomenclature Molecular formula – shows the actual number of atoms of each element in the compound Ex: hydrogen peroxide: H2O2 Chemical Nomenclature Structural formula – shows the number of atoms and the bonds between them Ex: hydrogen peroxide: H – O – O – H Chemical Nomenclature Monatomic Ions Members of a periodic table group have the same ionic charge For s-block cations, ion charge = group number Ex: Group 1: Na+, Group 2: Ba2+ Naming: element name + (cat)ion For p-block anions, ion charge = group number minus 18 Ex: Group 16: S2- Naming: ends with –ide Chemical Nomenclature Chemical Nomenclature Binary ionic compounds Cation: name of metal Anion: root name of nonmetal plus suffix –ide Binary ionic compound name: Cation + Anion Ex: sodium chloride, calcium bromide Chemical Nomenclature Binary ionic compounds Name the ionic compound formed and write their molecular formulas from the following pairs of elements: a. Magnesium and nitrogen b. Iodine and cadmium c. Strontium and fluorine d. Sulfur and caesium  Chemical Nomenclature Compounds with Metals that can form more than one ion Many metals, particularly the transition elements (d-block), can form more than one ion, each with its own particular charge. Names of compounds containing these elements include a Roman numeral with parentheses immediately after the metal ion’s name to indicate its ionic charge. In common names, the Latin root of the metal is followed by either of two suffixes: -ous for the ion with the lower charge -ic for the ion with the higher charge Ex: iron: Fe2+ = iron(II) = ferrous; Fe3+ = iron(III) = ferric Ex: iron(II) chloride = ferrous chloride; iron(III) chloride = ferric chloride Chemical Nomenclature Chemical Nomenclature Compounds with Metals that can form more than one ion Give the systematic and common names (if applicable) for the formulas or the formulas for the names of the following compounds: a. tin(II) fluoride b. CrI3 c. Ferric oxide d. CoS Chemical Nomenclature Chemical Nomenclature Chemical Nomenclature Chemical Nomenclature Chemical Nomenclature Acid names from Anion names When naming acids and writing their formulas, we consider them as anions connected to the number of hydrogen ions (H+) needed for charge neutrality. The two common types of acids are binary acids and oxoacids Chemical Nomenclature Acid names from Anion names Binary acid solutions form when certain gaseous compounds dissolve in water. Ex: gaseous hydrogen chloride (HCl) dissolves in water, it forms a solution whose name consists of the following parts: or hydrochloric acid. This naming pattern holds for many compounds in which hydrogen combines with an anion that has an –ide suffix. Chemical Nomenclature Acid names from Anion names Oxoacid names are similar to those of the oxoanions, except for two suffix changes: -ate in the anion becomes -ic in the acid -ite in the anion becomes –ous in the acid The oxoanion prefixes hypo- and per- are kept. Ex: BrO4-: perbromate; HBrO4: perbromic acid Chemical Nomenclature Acid names from Anion names Name the following anions and give the names and formulas of the acids derived from them: a. Br- b. IO3- c. CN- d. SO42- e. NO2- Chemical Nomenclature Names and Formulas of Binary Covalent Compounds Several are so familiar, such as ammonia (NH3), methane (CH4), and water (H2O), that we use their common names, but most are named in a systematic way: 1. The element with the lower group number in the periodic table is the first word in the name; the element with the higher group number is the second word. (Exception: When the compound contains oxygen and any of the halogens chlorine, bromine, and iodine, the halogen is named first.) 2. If both elements are in the same group, the one with the higher period number is named first. Chemical Nomenclature Names and Formulas of Binary Covalent Compounds Several are so familiar, such as ammonia (NH3), methane (CH4), and water (H2O), that we use their common names, but most are named in a systematic way: 3. The second element is named with its root and the suffix -ide. 4. Covalent compounds have Greek numerical prefixes to indicate the number of atoms of each element in the compound. The first word has a prefix only when more than one atom of the element is present; the second word usually has a numerical prefix. Chemical Nomenclature Names and Formulas of Binary Covalent Compounds 1. What is the formula of carbon disulfide? 2. What is the name of PCl5? 3. Give the name and formula of the compound whose molecules each consist of two N atoms and four O atoms. Chemical Nomenclature Naming Alkanes Alkanes – organic compounds that consist entirely of single- bonded carbon and hydrogen atoms. Any questions?