Chemical Bonding ©2011 University of Illinois Board of Trustees

Why do atoms form bonds? To lower the chemical potential energy ©2011 University of Illinois Board of Trustees

What is a Chemical Bond? Chemical Bond – The force that holds two atoms together.  Electrostatic force between oppositely charged particles.  There are three types of bonds: Ionic Covalent Metallic $ What about polar covalent? ©2011 University of Illinois Board of Trustees

Ionic Occurs between metals and nonmetals Involves the transfer of electron(s) The metal donates electron(s) to the nonmetal This results in formation of: (+) Cation (-) Anion Picture made on WebMO ©2011 University of Illinois Board of Trustees

Electrostatic attraction between cation and anion create the ionic bond. An electron is transferred from a cation to an anion in an ionic bond. Ionic Bonding ©2011 University of Illinois Board of Trustees

Lattice Structure ©2011 University of Illinois Board of Trustees

Covalent nonmetals Occurs between nonmetals sharing Involves the sharing of electron(s) Bond is overlap of electron clouds Two Types  Polar  Nonpolar ©2011 University of Illinois Board of Trustees

Polar Covalent Bond A covalent bond where the electrons are unequally shared. “Polar” means that the molecule has slightly positive and slightly negative poles. Caused by differences in electronegativities of elements that are bonded. H Cl Image from: htm&h=800&w=1000&sz=76&hl=en&start=23&um=1&tbnid=NpyhUO2LywGwRM:&tbnh=119&tbnw=149&prev=/images%3Fq%3Delectron%2Bdensity%2Bdiagrams%26start%3D20%26ndsp%3D20%26um%3D1%26 hl%3Den%26safe%3Dstrict%26rls%3DGWYG,GWYG: ,GWYG:en%26sa%3DN ©2011 University of Illinois Board of Trustees

Polar Covalent Image from: ©2011 University of Illinois Board of Trustees

Nonpolar Covalent Bond The electrons are equally shared. There are no partial charges or attractions between the molecules. H H Image made using WebMO ©2011 University of Illinois Board of Trustees

Nonpolar Covalent Image from: ©2011 University of Illinois Board of Trustees

Quick Review Increasing Electronegativity Difference Bonding CovalentIonic Sharing Polar Sharing Nonpolar ©2011 University of Illinois Board of Trustees

Metallic Bonding Bonding between metals Electrostatic attraction between electrons and metal ions Electrons = delocalized  “Sea of electrons” ©2011 University of Illinois Board of Trustees

% Ionic Character Tells you if your compound will be ionic, polar covalent, or nonpolar covalent ©2011 University of Illinois Board of Trustees

Electronegativity Image from: ©2011 University of Illinois Board of Trustees

Determining % Ionic Character % Ionic Character tells you to what degree a bond is covalent or ionic. It can be determined by subtracting the electronegativities of the elements in the bond. Bonds with electronegativity differences between  0  0.2 are nonpolar covalent  0.2  1.7 are polar covalent  1.7  higher are ionic ©2011 University of Illinois Board of Trustees

Examples What type of bond exists between NO, N 2, NaCl, and CaO?  N-O = = 0.40 = polar covalent  N-N = = 0 = nonpolar covalent  Na-Cl = = 2.23 = ionic  CaO = = 2.44 = ionic ©2011 University of Illinois Board of Trustees

Properties of Ionic Compounds Crystalline solids (made of ions) chem.ps.uci.edu/~potma/COSMOS/Lectur e6.ppt ©2011 University of Illinois Board of Trustees

Properties of Ionic Compounds High melting and boiling points Image from Microsoft Office ClipArt ©2011 University of Illinois Board of Trustees

Properties of Ionic Compounds Conduct electricity when melted Image from Microsoft Office ClipArt ©2011 University of Illinois Board of Trustees

Properties of Ionic Compounds Conduct electricity when dissolved in water Pickle Video ©2011 University of Illinois Board of Trustees

Properties of Ionic Compounds Many soluble in water but not in nonpolar liquids Animation Image from Microsoft Office ClipArt ©2011 University of Illinois Board of Trustees

Properties of Covalent Compounds Chlorine Gas Gases, liquids, or solids (made of molecules) Diamonds Water Images from Microsoft Office ClipArt ©2011 University of Illinois Board of Trustees

Properties of Covalent Compounds Low melting and boiling points Picture from: eeting/photo# ©2011 University of Illinois Board of Trustees

Properties of Covalent Compounds Poor electrical conductors in all phases Picture from: ©2011 University of Illinois Board of Trustees

Properties of Covalent Compounds Many soluble in nonpolar liquids but not in water ©2011 University of Illinois Board of Trustees

Properties of Metallic Compounds Strong Malleable Ductile Metallic Lustre Conductor of heat & electricity Images from Microsoft Office ClipArt ©2011 University of Illinois Board of Trustees

Chemical Bonding Quiz ©2011 University of Illinois Board of Trustees