November 25, 2014 Chemical Bonding: Ch 7 and 8 Chemical Bonding A chemical bond is a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together. Why are most atoms bound together? Most atoms are at relatively high potential energy by themselves and are more stable when combined with other elements! http://www.youtube.com/watch?v=QXT4OVM4vXI We will be discussing ionic vs. covalent bonding. http://www.youtube.com/watch?v=UR4eG60jjQQ Chapter 7- Ionic Bonding http://www.youtube.com/watch?v=QqjcCvzWwww Chapter 8- Covalent Bonding Chemical Bonding-Vocabulary Chemical Bonding-Vocabulary Chemical Formula A chemical bond ionic covalent -Attractive force between atoms or ions that binds them Formula Unit Molecular Formula together as a unit. NaCl H2O -bonds form in order to: -decrease potential energy (PE) -increase stability Chemical Bonding-Vocabulary Chemical Bonding-Vocabulary Compound Ion 2 elements more than 2 elements 1 atom 2 or more atoms Binary Compound Ternary Compound Monoatomic Ion Polyatomic Ion + - NaCl NaNO3 Na NO3 November 25, 2014 B) Types of Bonds 1) Ionic Bonding Ionic Covalent Metallic electrons electrons electrons are transferred shared delocalized -Transfer of electrons from one atom to Bond Formation from metal to between two among metal nonmetal nonmetals atoms. another. Type of Structure crystal lattice true molecules "electron sea" Metal + Nonmetal Ionic Compound Physical State solid liquid or gas solid Valence electrons are usually the only electrons used in chemical bonds. Melting Point high low very high Solubility in yes usually not no Water Electrical yes (solution no yes (any form) Conductivity or liquid) malleable, Other Properties odorous ductile, lustrous NaCl, BaCl2, Example H2O, NO, NO2 Al, Fe, etc. CaO, etc. Example: Sodium Chloride The chemical formula: NaCl Steps: because Na+1 and Cl-1 1. Look at the charge 2. Determine the ratio Atoms of metals tend to lose their valence electrons, leaving of charges a complete octet in the next-lowest energy level. 3. Criss-Cross the charges and simplify Atoms of some non-metals tend to gain electrons or to to the lowest ratio. share electrons with another nonmetal to achieve a complete octet. Nomenclature of Ionic Compounds Practice Problems: 1. Keep the name of the cation the same and change the name of the anion to an -ide ending. Determine the charge of the ions and the final formula unit of the following: a) NaCl= sodium chloride b) CaCl2= calcium chloride 1. potassium and iodine c) BaF2= 2. aluminum and oxygen d) KCl= 3. magnesium and chlorine e) MgO= November 25, 2014 Coordination patterns and packing depends on the size of the ions. Remember the trends from the Periodic Table! http://www.youtube.com/watch?v=KNgRBqj9FS8 Body Centered Cubic Oxidation Numbers (Honors) Every atom has 8 neighbors -Can figure out from the formula Ex: (Na, K, Fe) -Unpaired electrons in d orbitals http://www.youtube.com/watch?v=ZVqocQLAEr0 Face Centered Cubic Fe: (+2 and +3) Every atom has 12 neighbors Ex: (Ag, Au, Al, Pb) http://www.youtube.com/watch?v=Rm-i1c7zr6Q&feature=related Hexagonal close-packed Every atom ALSO has 12 neighbors but is pattern is different. Ex: (Zn, Mg, and Cd) Section 7.3 Bonding in Metals *Similar to structure of ionic! The valence electrons of metal atoms can be modeled as a Bonding in Metals sea of electrons. The valence electrons are mobile and can drift freely from Metallic bonds: one part of the metal to another. consist of the attraction of the free-floating valence The electrons can drift because of the vacant d orbitals just electrons for the positively charged metal ions. below their highest energy level. These orbitals can overlap and the overlapping is what causes the electrons to move about freely. http://www.drkstreet.com/resources/metallic-bonding-animation.swf November 25, 2014 Crystalline Structure of Metals Alloys: Mixtures composed of two or more elements, at least one of which is a metal. *Alloys are important because their properties are often superior to those of their component elements. Types of Alloys 3) Covalent Bonding Substitutional- atoms of different Electrons shared between nonmetals components are of similar size. Ex: Brass Interstitial- solute atoms occupy "gaps" because they are different sizes. Ex: Carbon for steel Potential Energy Diagram B(r)illiant Harvard Nerds Mr. BrINClHOF Often Find 4. 3. 2. 1. C(l)hemistry Interesting Most elements can form diatomics, HOWEVER, only at very high temperatures. Kinetic Theory (Random movement) 1. The separated atoms do not affect each other. 2. Potential energy decreases as the atoms are drawn together. The "7" exist free at normal conditions. 3. Potential energy is at a minimum when attractive forces are balanced by repulsive forces. 4. Potential increases when repulsion between like charges outweighs attraction between opposite charges. November 25, 2014 The Nature of Covalent Bonding 1. Single Covalent Bond In covalent bonds, electron sharing usually occurs so that Structural formula: atoms attain the electron configurations of noble gases. Represents the covalent bonds by dashes and shows the arrangement of covalently bonded atoms. One dash represents two electrons. Why would atoms want to do that? We will be looking at three different types of covalent Unshared Pair: bonds: 1. Single Covalent A pair of valence electrons that are not shared between atoms. 2. Double and Triple Covalent (lone pair or nonbonding pair). 3. Coordinate Covalent 2. Double and Triple Covalent Bonds 3. Coordinate Covalent Bonds Atoms form double or triple covalent bonds if they can attain Coordinate Covalent Bond: a noble gas structure by sharing two pairs or three pairs of electrons. A covalent bond in which one atom contributes both bonding electrons. Double covalent bond: A bond that involves two shared pairs of electrons In a coordinate covalent bond, the shared electron pair comes from one of the bonding atoms. Triple covalent bond: A bond formed by sharing three pairs of electrons. Electron-Dot Notation (Lewis Dot Structures) Lewis Structures-Steps Why the exceptions?? 1. Find the total # of valence electrons Incomplete Octet: (Group 3A) 2. Arrange atoms-singular atom is usually in the middle (usually carbon) 3. Form bonds between atoms (2 electrons) Group 3A: Boron 1s2 2s2 2p1 (only 3 valence electrons) 4. Distribute remaining electrons to give each atom an octet. Expanded Octet: (3rd Period) 5. If there are not enough electrons to go around, you will have to make double or triple bonds. Beyond the 3rd period with the "d" orbitals · Don't forget the exceptions. · Boron and Aluminum only need 6 Sulfur: [Ne]3s2 3p4 (6 valence electrons) · Sulfur and Phosphorus can have an expanded octet. Odd-Electron Molecules (Radicals) (NO and NO2 ) November 25, 2014 Lewis Structures-Practice Polyatomic Ions -a tightly bound group of atoms that have a positive or NH3 negative charge and behaves as a unit. The charge is on the whole ion but the individual components can be held together covalently. CO2 + Example is the ammonium ion (NH4 ) Polyatomic Ions-Practice Exceptions to Lewis Structures 1. Odd number of valence electrons - ClO4 *Central atom will not have an octet *Examples: ClO2 and NO 2. Central atom with less than eight electrons *These compounds tend to be very reactive *Examples: BF3, BH3 3. Central atom with more than eight electrons *Most common exception + *Expanded octet NH4 *extra electrons fill in the empty d-sublevel *Examples: SF6, XeF4 Resonance Resonance-Practice O3 SO3 November 25, 2014 Bond Dissociation Energies Bond Dissociation Energy: Nomenclature (Intro) The energy required to break the bond between two covalently bonded atoms. The larger the bond dissociation energy, the stronger the bond Example: C2H2 vs. C2H6 Nomenclature (Intro) Nomenclature (Intro) Name the following binary molecular compounds: 1. SF6 is sulfur hexafluoride 2. CO 3. CO2 4. N2 O 5. Cl2 O8 Resonance (Honors Only) Formal Charge is used to determine the best overall resonance structure. Handout.