CHM 1020 Chp 5
CHM 1020 Chp 5 CHM 1020
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This 10 page Class Notes was uploaded by Rachel Belson on Thursday February 18, 2016. The Class Notes belongs to CHM 1020 at Wayne State University taught by Maryfrances Barber in Fall 2015. Since its upload, it has received 28 views. For similar materials see Survey of General Chemistry in Chemistry at Wayne State University.
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Date Created: 02/18/16
Chapter 5 Monday, February 15, 2016 8:14 PM 5.1 The Covalent Bond Model 1. Ionic bonds form between atoms of dissimilar elements (metal and nonmetal). Covalent bonds form between similar or even identical atoms. 2. Electron transfer is the mechanism by which ionic bonds form. Covalent bonds occur when electron pairs are shared. 3. Ionic compounds do not contain discrete molecules. Instead, such compounds consist of an extended array of alternating positive and negative ions. In covalently bonded compounds, the basic structural unit is a molecule. Indeed such compounds are called molecularcompounds. 4. All ionic compounds are solids at room temperature. Molecular compoundsmay be solids, liquids, or gases at room temperature. 5. An ionic solid, if soluble in water, forms and aqueous solution that conducts electricity. The electrical conductance is related to the presence of ions (charged particles) in the solution. A molecular compound, if soluble in water usually produces a nonconducting aqueous solution. Covalent Bond: chemical bond resulting from two nuclei attracting the same shared electrons. 5.2: Lewis Structures for Molecular Compounds Bonding electrons: pairs of valence electrons that are shared between atoms in a covalent bond. Nonbonding electrons: pairs of valence electrons on an atom that are not involved in electron sharing. 5.3 Single, Double, and Triple Covalent Bonds Single Covalent Bond: a covalent bond in which two atoms share one pair of electrons. Double Covalent Bond: a covalent bond in which two atoms share two pairs of electrons. Triple Covalent Bond: a covalent bond in which two atoms share three pairs of electrons. 5.4 Valence Electrons and Number of Covalent Bonds Formed Not all elementscan form double or triple bonds. They have to have at least two vacancies in an atoms valence electron shell. 5.5 Coordinate Covalent Bonds Coordinate Covalent bond: a covalentbond in which both electrons in a shared pair of electrons came from one of the two atoms in the bond. Once the bond is formed, there is no way of distinguishing the electrons' source. 5.6 Systematic Procedures for Drawing Lewis Dot Structures 1. Calculate the number of valence electrons available in the moleculeby adding together the valence electron counts for all atoms in the molecule. 2. Write the chemical symbols of the atoms in the moleculein the order in which they are bonded to one another, and then place a single covalentbond involving two electrons,between each pair of bonded atoms. a. Determining the central atom is key. The central atom is the atom that has the most other atoms bonded to it. For commonbinary molecular compounds, the central atom is the atom that appears only once in the formula. S in SO3. In molecular compounds containing hydrogen, oxygen, and an additional element, the additional element is the central atom. In that case, the oxygen is bonded to the central atom, and the hydrogen is bonded to the oxygen. Carbon is the central atom in nearly all carbon-containing compounds. Hydrogen or fluorine is never the central atom. 3. Add nonbonding electronpairs to the structure such that each atom bonded to the central atom has an octet of electrons. REMEMBER: hydrogen's "octet" is only two electrons. 4. Place any remaining electronson the central atom of the structure. 5. If there are not enough electrons to give the central atom an octet, then use one or more pairs of nonbonding electrons on the atoms bonded to the central atom to form a double or triple bond. 6. Count the total number of electronsin the completed Lewis structure to make sure it is equal to the number of valence electrons available for bonding, the number calculated in step one. 5.7 Bonding in Compounds with Polyatomic Ions Present Polyatomicsare drawn differently than other structures. The polyatomicion has parentheses drawn around it, and then the atoms bonded to the ion are connected outside the parentheses. 5.8 Molecular Geometry Molecular Geometry: the description of the three dimensional arrangement of atoms within a molecule. VSEPR Theory: set of procedures for predicting the molecular geometry of a molecule using the information contained in the molecule's Lewis structure. 1. Linear a. Two electron pairs (as far as possible from each other) are found on opposite sides of a nucleus, 180 degrees apart. 2. Trigonal planar a. Three electron pairs (as far as possible from each other) are found at the corners of an equilateral triangle. 120 degree angles between them. 3. Tetrahedral a. Minimizes repulsions among four sets of electron pairs. All four sides are identical equilateral triangles. The angle between any two electrons is 109 degrees. VSEPR Electron Group: a collectionof valence electronspresent in a localized region about the central atom in a molecule. These are single, double or triple bonds. A single, double, or triple bond are all equally counted as "one electron group," because each space takes up one region of space about the atom. All moleculeswith two VSEPR electron groups are linear. Moleculeswith three VSEPR electron groups are either trigonal planar or angular. a. Angular when all three groups are bonding b. Trigonal planar when one of three groups is nonbonding. Moleculeswith four VSEPR electron groups are tetrahedral (no nonbonding groups are present), trigonal pyramidal (one nonbonding group), or angular (two nonbonding groups). Exam 2 Page 1 nonbonding group), or angular (two nonbonding groups). When molecules have more than one central atom,the central atoms can be looked at separately and then combining the results. 5.9 Electronegativity Electronegativity: a measure of the relative attraction that an atom has for the shared electrons in a bond. Electronegativityvalues increase from left to right across periods and from bottom to top within groups 5.10 Bond Polarity Bond Polarity: a measure of the degree of inequality in the sharing of electrons between two atoms in a chemical bond. Nonpolar covalent bond: a covalentbond in which there is equal sharing of electrons between two atoms. Polar Covalent Bond: a covalentbond in which there is unequal sharing of electrons between two atoms. 1. Bonds that involved atoms with the same or very similar electronegativitiesare nonpolar covalentbonds. Electronegativitydifferences of .4 or less 2. Bonds with electronegativitydifferences greater than .4 but less than 1.5 are polar covalentbonds. 3. Bonds with an electronegativitydifference greater than 2 are called ionic bonds. 4. Bonds with an electronegativitydifference between 1.5 and 2 are considered ionic if the bond involvesa metal and a nonmetaland polar covalent if it contains 2 nonmetals. 5.11 Molecular Polarity Molecular polarity: a measure of the degree of inequality in the attraction of bonding electrons to various location within a molecule. Polar Molecule: a molecule in which there is an unsymmetricaldistribution of electronic charge. Nonpolar Molecule: a molecule in which there is a symmetricaldistribution of electroniccharge. 5.12 Recognizingand Naming Binary Molecular Compounds Binary Molecular Compound: a molecular compound in which only two nonmetallic elementsare present. a. Naming: the full name of the nonmetal of lower electronegativityis given first, followed by a separate word containing the stem of the name of the more electronegative nonmetal followedby the suffix -ide. b. Using prefixes is also necessary. ***when there is only 1 atom of the first named elementin the compound, only the element's name is written, without mono. 1 Mono 2 Di 3 Tri 4 Tetra 5 Penta 6 Hexa 7 Hepta 8 Octa 9 Nona 10 deca Exam 2 Page 2 Exam 2 Page 3 Exam 2 Page 4 Exam 2 Page 5 Exam 2 Page 6 Exam 2 Page 7 Exam 2 Page 8 Exam 2 Page 9 Exam 2 Page 10
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