Transcript CH 6
6-1 Introduction to Chem Bonding *a link between atoms that results from the mutual attraction of their nuclei for e- -Types of chem bonds 1. Ionic bond: transfer of e2. Covalent bond: sharing of e-’s -bonds between unlike atoms are never completely ionic and rarely completely covalent.(Pauling) 3. Metallic bonds: between metals *nonpolar-covalent bond: cov bond which the bonding e-’s are shared equally by the bonded atoms -resulting in a balanced distribution of elect charge *Polar: meaning that they have an uneven distribution of charge *Polar-cov bond: the united atoms have an unequal attraction for the shared e-’s -Why chem bonding occurs -if their PE is lowered by the change, two atoms will form a chem bond. 6-2 Covalent Bonding and Molecular Compounds *Molecule: smallest unit quantity of matter which can exist by itself and retains all the prop of the original substances *Diatomic molecule: 2 like atom *Molecular cmpnd: chem cmpnd whose simplest units are molecules *Chem formula: represents the #’s of atoms of each kind in a chem cmpnd by using atomic symbols and numerical subscripts A. Vocabulary CHEMICAL FORMULA IONIC COVALENT Formula Unit Molecular Formula NaCl CO2 *Molecular formula: shows types and numbers of atoms combined in a single molecule -Formation of covalent bond *Bond length: aver dist between 2 bonded atoms *Bond nrg: nrg required to break a chem bond and form neutral atoms -The Octet Rule *Octet rule: 8 e-’s in the highest nrg level -Lewis Structure (Gilbert Lewis) *pg 169 -Lewis Structure *Unshared pair: pair of e-’s that is not involved in bonding *single bond: cov bond produced by sharing of 1 pair of e-’s between 2 atoms *structural formula: indicates kind, number, arrangement, and bonds of the atoms in a molecule. -Multiple Covalent Bonds *Double bond: cov bond between 2 atoms produce by sharing 2 pairs of eEX -Multiple Covalent Bonds *Triple bond: cov bond between 2 atoms produced by sharing 3 pairs of eEx -Sample problem 6.3 -Polyatomic Ions *charged group of cov bonded atoms Ex 6.3 Ionic Bonding and Ionic Compounds *Ionic compound: composed of + and – ions combined so that the + and – charges are equal 6.3 Ionic Bonding and Ionic Compounds *Formula unit: simplest collection of atoms from which a cmpnds formula can be estab -Common ions: Na+, K+, Mg+2, Ca+2, Ba+2, -Formation of Ionic Bonds *Lattice nrg: nrg released when one mole of an ionic crystalline cmpnd is formed from gaseous ions -Ionic vs Covalent bonds -ionic bonds are stronger than cov bonds -cov bonds ~lower mp, bp, and hardness -Ionic vs Covalent bonds -ionic bonds ~hard and brittle ~carry a current when dissolved in water B. Types of Bonds IONIC COVALENT Bond Formation e- are transferred from metal to nonmetal e- are shared between two nonmetals Type of Structure crystal lattice true molecules Physical State solid liquid or gas Melting Point high low Solubility in Water yes usually not Electrical Conductivity yes (solution or liquid) no Other Properties odorous 6.4 Metallic Bonding -metals have a low ionization nrg and low electroneg. -two metals form at best a weak covalent bond 6.4 Metallic Bonding -metals tend to form what we call a sea of electrons 6.4 Metallic Bonding *Metallic bond: chem bond resulting from the attraction between + ions and surrounding mobile electrons -to compare strengths in metals vaporization heats are used B. Types of Bonds METALLIC Bond Formation e- are delocalized among metal atoms Type of Structure “electron sea” Physical State solid Melting Point very high Solubility in Water no Electrical Conductivity yes (any form) Other Properties malleable, ductile, lustrous -Nature of Metals -the motion of the e- sea helps explain why metals have certain properties *Malleability *Ductility -luster B. Types of Bonds RETURN B. Types of Bonds RETURN B. Types of Bonds Ionic Bonding - Crystal Lattice RETURN B. Types of Bonds Covalent Bonding - True Molecules Diatomic Molecule RETURN B. Types of Bonds Metallic Bonding - “Electron Sea” RETURN C. Bond Polarity Most bonds are a blend of ionic and covalent characteristics. Difference in electronegativity determines bond type. C. Bond Polarity Electronegativity Attraction an atom has for a shared pair of electrons. higher e-neg atom lower e-neg atom + C. Bond Polarity Electronegativity Trend (p. 151) Increases up and to the right. C. Bond Polarity Nonpolar Covalent Bond e- are shared equally symmetrical e- density usually identical atoms C. Bond Polarity Polar Covalent Bond e- are shared unequally asymmetrical e- density results in partial charges (dipole) + C. Bond Polarity Nonpolar Polar Ionic View Bonding Animations. C. Bond Polarity Examples: Cl2 3.0-3.0=0.0 Nonpolar HCl 3.0-2.1=0.9 Polar NaCl 3.0-0.9=2.1 Ionic 6.5 The properties of molecular compounds -VSEPR Theory *electrostatic repulsion between valence e- pairs surrounding an atom causes these pairs to be oriented as far apart as possible (table 6-5 pg 186) 1. 2. 3. 4. Linear Tetrahedral Trigonal pyramidal Bent -Hybridization(fig.6-23 p188) *mixing of two or more atomic orbitals of similar nrg’s on the same atom to give new orbital of equal nrg’s -Hybridization ex: CH4 -hybridization of s and p yield 4 new identical orbits *hybrid orbitals: orb of = nrg produced by the combination of 2 or more orb on the same atom -Intermolecular Forces *force of attraction between molecules -generally weaker than the bonds that join atoms in molecules, ions in ionic cmpnds, or metal atoms in solid metals ~dipole-dipole forces and molecular polarity -strongest intermol forces act between polar molecules *dipole: = but opp charges separated by a short distance. - arrow points toward the neg pole *DD force: forces of attraction between polar molecules ex: polar vs nonpolar ~hydrogen bonding *an intermolecular attraction between a H atom and an unshared pair of e-’s on a strongly electroneg. Atom ~hydrogen bonding -H bond represented by dotted lines connecting the H to the unshared e- pair of the electroneg atom ~london dispersion forces (Fritz London 1930) *attraction resulting from the constant motion of e-’s and the certain instantaneous dipoles and induced dipoles ~london dispersion forces -between all atoms and molecules -only intermolecular forces acting among noble-gas atoms and nonpolar molecules -LF increases with increasing mass of atoms and molecules