08+Covalent+Bonding

= = 8.1 Molecular Compounds 8.2 The Nature of Covalent Bonding 8.3 Bonding Theories 8.4 Polar Bonds and Molecules
 * How are the melting points and boiling points of molecular compounds different from those of ionic compounds?
 * What information does a molecular formula provide?
 * What is the result of electrons sharing in covalent bonds?
 * How do electron dot structures represent shared electrons?
 * How do atoms form double or triple covalent bonds?
 * How are coordinate covalent bonds different from other covalent bonds?
 * How is the strength of a covalent bond related to its bond dissociation energy?
 * How are oxygen atoms bonded in ozone?
 * What are some expectations to the octet rule?
 * How are atomic and molecular orbitals related?
 * How does VSEPR theory help predict the shape of molecules?
 * In what ways is orbital hybridization useful in describing molecules?
 * How do electronegativity values determine the charge distribution in a polar bond?
 * What happens to polar molecules between a pair of oppositely charged metals plates?
 * How do intermolecular attractions compare with ionic and covalent bonds?
 * Why do network solids have high melting points?

=Outlined Notes= 8.1 Molecular Compounds > A. Molecules and Molecular Compounds >> 1. __Covalent bond__- Atoms held together by sharing electrons >> 2. __Molecule__- A neutal group of atoms joined together by covalent bonds. >> 3. __Diatomic molecule-__ a molecule consisting of two atoms. >>> (a) Example: Oxygen >> 4. __Molecular compound__- A compound composed of molecules >>> (a) Example: Water 5. * Molecular compounds tend to have a relatively low meltind and boiling points than ionic compounds. B. Molecular Formulas 1. __Molecular formula__- The chemical formula of a molecular compound. (a) Example: Water- H2O 2. * A molecular formula shows how many atoms of each element a molecule contians.

8.2 The Nature of Covalent Bonding A. The Octet Rule in Covalent Bonding 1.* In colvalent bonds, electrons sharing usually occurs so that atoms attain the electron configurations of noble gases. B. Single Covalent Bonds 1. __Single covalent bond-__ Two atoms held together by sharing a pair of electrons 2. *An electron dot structure such as H:H represents the shared pair of electrons of the covalent bond by two dots. 3. __Structural formula-__ Represents the covalent bonds by dashes (H - H) and shows the arrangement of covalently bonded atoms. 4. __Unshared pair-__ A pair of valence elections that is not shared between atoms (a) Also known as a lone pair or a nonbonding pair B. Double and Triple Covalent Bonds 1.* Atoms form double or triple covalent bonds if they can attain a noble gas structure by sharing two pairs or three pairs of electrons. 2. __Double covalent bond__- A bond that involes two shared pairs of electrons. 3. __Triple covalent bond-__ A bond formed by sharing three pairs of electrions. C. Coordinate Covalent Bonds 1. __Corrdinate covalent bond-__ A covalent bond in which one atom contributes bothe bonding electrons 2.* In a coordinate covalent bond, the shared electron pair comes from one of the bonding atoms. 3. __Polyatomic ion-__ atightly bound group of atoms that has a positive or negative change and behaves as a unit. C. Bond Dissociation Energies 1. __Bond dissociation energy-__ The energy required to break the bond between two covalently bonded atoms 2.* A large bond dissociation energy corresponds to a strong covalent bond. D. Resonance 1.* The actual bonding of oxygen atoms in ozone is hybrid, or mixture., of the extremes represented by the resonance forms. 2. __Resonance structure-__ A structure that occurs when it is possible to draw two or more valid electron dot structures that have the same number of electron pairs for a molecule or ion. 3. *Ozone consists of one single coordinate covalent bond and one dounble covalent bond. E. Exceptions to the Octet Rule 1.* The octet rule cannot be satisfied in molecules whose total number of valence electrons is an odd number. There are also molecules in which an atom has fewer, or more, than a complete octet of valence electrons.

8.3 Bonding Theories A. Molecular Orbitals 1. __Molecular orbitals-__ orbitals that apply to the entire molecule. 2.*Just as an atomic orbital belongs to a paritcular atom, a molecular orbital belongs to a molecule as a whole. 3.__Bonding orbitals-__ A molecular orbital that can be occupied by two electrons of a covalent bond 4.__Sigma bond-__ When two atomic orbitals combine to form a molecular orbital that is symmetrical around the azis connectiong two atomic nuclei (a) Symbol: σ 5. __Pi bond__- When a pi molecular orbital is filled with two electrons B. VSEPR Theory 1.* Valence-shell electron pair repulsion theory- The repulsion between electron pairs causes molecular shapes to adjust so that the valece-electron pairs stay as far apart as possible. 2.__Hybridization-__ Several atomic orbitals mix to form the same total number of equicalent hybrid orbitals.

8.4 Polar Bonds and Molecules A. Bond Polarity 1. __Nonpolar covalent bond-__ When the atom in the bond pull equally (as occurs when identical atoms are bonded), the bonding electrons are shared equally. (a) Examples: Hydrogen, Oxygen, Nitrogen, and diatomic halogen molecules 2. __Polar covalent bond/Polar bond-__ A covalent bond between atoms in which the electrons are shared unequally. 3.* The more electronegative atom attracts electrons more strongly and gains a slightly negative charge. The less electonegative atom has a slightly positive charge. B. Polar Molecules 1.__Polar molecule-__ One end of the molecule is slightly negative and the other end is slightly positive. (a) The presence of a polar bond in a molecule often makes the entire molecule polar. C. Attractions Between Molecules 1.* Intermolecular attractions are weaker than either ionic or covalent bonds. 2. __Van der Waals forces-__ The two weakest attractions between molecules (a) Named after Dutch chemist, Johannes ven der Waals 3. __Dipole interactions-__ the weakest of all molecular interactions, are caused by the motion of electrons. 4. __Hydrogen bonds__- attractive forces in which a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electon pair of aother electronegative atom. D. Intermolecular Attractions and Molecular Properties 1. __Network solids-__ solids in which all of the atoms are covalently boned to each other. 2.* Melting a network solid would require breaking covalent bonds throughout the solid.

=Reference Pages=









=Practice Problems= Determine the number of valence electrons in neutral atoms of the following elements: (a) Si (b) Mn (c) Sb (d) Pb

=Assignments=

=Labs=
 * [|http://74.125.47.132/search?q=cache:H7J07Cjm5ZkJ:www.pkwy.k12.mo.us/homepage/jjauss/File/chemistry_I/Bonding/Ionic_vs._Covalent_Lab(1).pdf+Covalent+Bonding+labs&cd=1&hl=en&ct=clnk&gl=us] Ionic Vs. Covalent Bonding**

=Sample Test= [|Review Questions - http://www.sciencegeek.net/Chemistry/taters/Unit3review.htm] [] [] [] [] []

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