General orrganic and biological chemistry structures off liffe 5th by karen timberlake06 worked examples

Sample Problem 6.1 Ions a Write the symbol and name for the ion that has protons and 10 electrons b Write the symbol and name for the ion that has 20 protons and 18 electrons Solution a The element with seven protons is nitrogen In an ion of nitrogen with 10 electrons, the ionic charge would be 3–, [(7+) + (10–) = 3–] The ion, written as N3–, is the nitride ion b The element with 20 protons is calcium In an ion of calcium with 18 electrons, the ionic charge would be 2+, [(20+) + (18–) = 2+] The ion, written as Ca2+, is the calcium ion Study Check 6.1 How many protons and electrons are in each of the following ions? a S2– b Al3+ Answer a 16 protons, 18 electrons b 13 protons, 10 electrons General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.2 Writing Symbols for Ions Consider the elements aluminum and oxygen a Identify each as a metal or a nonmetal b State the number of valence electrons for each c State the number of electrons that must be lost or gained for each to achieve an octet d Write the symbol, including its ionic charge, and name for each resulting ion Solution Study Check 6.2 Write the symbols for the ions formed by potassium and sulfur Answer K+ and S2– General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.3 Writing Formulas from Ionic Charges Write the symbols for the ions, and the correct formula for the ionic compound formed when lithium and nitrogen react Solution Lithium, which is a metal in Group 1A (1), forms Li+; nitrogen, which is a nonmetal in Group 5A (15), forms N3– The charge of 3– is balanced by three Li+ ions 3(1+) + 1(3–) = Writing the cation (positive ion) first and the anion (negative ion) second gives the formula Li3N Study Check 6.3 Write the symbols for the ions, and the correct formula for the ionic compound that would form when calcium and oxygen react Answer Ca2+, O2–, CaO General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.4 Naming Ionic Compounds Write the name for the ionic compound Mg3N2 Solution Step Identify the cation and anion The cation, Mg2+, is from Group 2A (2), and the anion, N3–, is from Group 5A (15) Step Name the cation by its element name The cation Mg2+ is magnesium Step Name the anion by using the first syllable of its element name followed by ide The anion N3– is nitride Step Write the name for the cation first and the name for the anion second Mg3N2 magnesium nitride Study Check 6.4 Name the compound Ga2S3 Answer gallium sulfide General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.5 Naming Ionic Compounds with Variable Charge Metal Ions Antifouling paint contains Cu2O, which prevents the growth of barnacles and algae on the bottoms of boats What is the name of Cu2O? Solution Step Determine the charge of the cation from the anion General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.5 Naming Ionic Compounds with Variable Charge Metal Ions Continued Step Name the cation by its element name and use a Roman numeral in parentheses for the charge copper(I) Step Name the anion by using the first syllable of its element name followed by ide oxide Step Write the name for the cation first and the name for the anion second copper(I) oxide Study Check 6.5 Write the name for the compound with the formula Mn2S3 Answer manganese(III) sulfide General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.6 Writing Formulas for Ionic Compounds Write the correct formula for iron(III) chloride Solution Step Identify the cation and anion Iron(III) chloride consists of a metal and a nonmetal, which means that it is an ionic compound General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.6 Writing Formulas for Ionic Compounds Continued Step Balance the charges Step Write the formula, cation first, using subscripts from the charge balance FeCl3 Study Check 6.6 Write the correct formula for chromium(III) oxide Answer Cr2O3 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.7 Writing Formulas Containing Polyatomic Ions An antacid called Amphojel contains aluminum hydroxide, which treats acid indigestion and heartburn Write the formula for aluminum hydroxide Solution Step Identify the cation and polyatomic ion (anion) Cation Polyatomic ion (anion) aluminum hydroxide 3+ Al OH– Step Balance the charges Step Write the formula, cation first, using the subscripts from charge balance The formula for the compound is written by enclosing the formula of the hydroxide ion, OH–, in parentheses and writing the subscript outside theChemistry: right parenthesis © 2016 Pearson Education, Inc General, Organic, and Biological Structures of Life, 5/e Karen C Timberlake Sample Problem 6.7 Writing Formulas Containing Polyatomic Ions Continued Study Check 6.7 Write the formula for a compound containing ammonium ions and phosphate ions Answer (NH4)3PO4 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.10 Writing Formulas for Molecular Compounds Continued Study Check 6.10 Write the formula for the molecular compound iodine pentafluoride Answer IF5 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.11 Naming Ionic and Molecular Compounds Identify each of the following compounds as ionic or molecular and give its name: a K3P b NiSO4 c SO3 Solution a K3P, consisting of a metal and a nonmetal, is an ionic compound As a representative element in Group 1A (1), K forms the potassium ion, K+ Phosphorus, as a representative element in Group 5A (15), forms a phosphide ion, P3– Writing the name of the cation followed by the name of the anion gives the name potassium phosphide b NiSO4, consisting of a cation of a transition element and a polyatomic ion SO 42–, is an ionic compound As a transition element, Ni forms more than one type of ion In this formula, the 2– charge of SO 42– is balanced by one nickel ion, Ni2+ In the name, a Roman numeral written after the metal name, nickel(II), specifies the 2+ charge The anion SO42– is a polyatomic ion named sulfate The compound is named nickel(II) sulfate c SO3 consists of two nonmetals, which indicates that it is a molecular compound The first element S is sulfur (no prefix is needed) The second element O, oxide, has subscript 3, which requires a prefix tri in the name The compound is named sulfur trioxide Study Check 6.11 What is the name of Fe(NO3)3? Answer iron(III) nitrate General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.12 Drawing Lewis Structures Draw the lewis structure for PCl3, phosphorus trichloride, used commercially to prepare insecticides and flame retardants Solution Step Determine the arrangement of atoms In PCl3, the central atom is P because there is only one P atom Cl Step P Cl Cl Determine the total number of valence electrons We use the group number to determine the number of valence electrons for each of the atoms in the molecule Step Attach each bonded atom to the central atom with a pair of electrons Each bonding pair can also be represented by a bond line © 2016 Pearson Education, Inc General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake Sample Problem 6.12 Drawing Lewis Structures Continued Step Place the remaining electrons using single or multiple bonds to complete the octets Six electrons (3 × e–) are used to bond the central P atom to three Cl atoms Twenty valence electrons are left 26 valence e– – bonding e– = 20 e– remaining We use the remaining 20 electrons as lone pairs, which are placed around theouter Cl atoms and on the P atom, such that all the atoms have octets Study Check 6.12 Draw the Lewis structure for Cl2O Answer General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.13 Drawing Lewis Structures for Polyatomic Ions Sodium chlorite, NaClO2, is a component of mouthwashes, toothpastes, and contact lens cleaning solutions Draw the Lewis structure for the chlorite ion, ClO2– Solution Step Determine the arrangement of atoms For the polyatomic ion ClO 2–, the central atom is Cl because there is only one Cl atom For a polyatomic ion, the atoms and electrons are placed in brackets, and the charge is written outside to the upper right [O Cl O]– Step Determine the total number of valence electrons We use the group numbers to determine the number of valence electrons for each of the atoms in the ion Because the ion has a negative charge, one more electron is added to the valence electrons General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.13 Drawing Lewis Structures for Polyatomic Ions Continued Step Attach each bonded atom to the central atom with a pair of electrons Each bonding pair can also be represented by a line, which indicates a single bond Step Place the remaining electrons using single or multiple bonds to complete the octets Four electrons are used to bond the O atoms to the central Cl atom, which leaves 16 valence electrons Of these, 12 electrons are drawn as lone pairs to complete the octets of the O atoms The remaining four electrons are placed as two lone pairs on the central Cl atom Study Check 6.13 Draw the Lewis structure for the polyatomic ion NH2– Answer General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.14 Drawing Lewis Structures with Multiple Bonds Draw the Lewis structure for carbon dioxide, CO2, in which the central atom is C Solution Step Determine the arrangement of atoms O C O Step Determine the total number of valence electrons Using the group number to determine valence electrons, the carbon atom has four valence electrons, and each oxygen atom has six valence electrons, which gives a total of 16 valence electrons Step Attach each bonded atom to the central atom with a pair of electrons O : C : O or O—C—O Step Place the remaining electrons to complete octets Because we used four valence electrons to attach the C atom to two O atoms, there are 12 valence electrons remaining 16 valence e– – bonding e– = 12 e– remaining General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.14 Drawing Lewis Structures with Multiple Bonds Continued The 12 remaining electrons are placed as six lone pairs of electrons on the outside O atoms However, this does not complete the octet of the C atom To obtain an octet, the C atom must share lone pairs of electrons from each of the O atoms When two bonding pairs occur between atoms, it is known as a double bond Study Check 6.14 Draw the Lewis structure for HCN, which has a triple bond Answer General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.15 Bond Polarity Using electronegativity values, classify each of the following bonds as nonpolar covalent, polar covalent, or ionic: O—K, Cl—As, N—N, P—Br Solution For each bond, we obtain the electronegativity values and calculate the difference in electronegativity Study Check 6.15 Using electronegativity values, classify each of the following bonds as nonpolar covalent, polar covalent, or ionic: a P—Cl b Br—Br c Na—O Answer a polar covalent (0.9) b nonpolar covalent (0.0) c ionic (2.6) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.16 Shapes of Molecules Predict the shape of a molecule of SiCl4 Solution Step Draw the Lewis structure Using 32 e–, we draw the bonds and lone pairs for the Lewis structure of SiCl4 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.16 Shapes of Molecules Continued Step Arrange the electron groups around the central atom to minimize repulsion To minimize repulsion, the electron-group geometry would be tetrahedral Step Use the atoms bonded to the central atom to determine the shape Because the central Si atom has four bonded pairs and no lone pairs of electrons, the SiCl4 molecule has a tetrahedral shape Study Check 6.16 Predict the shape of SCl2 Answer The central atom S has four electron groups: two bonded atoms and two lone pairs of electrons The shape of SCl is bent, 109° General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.17 Predicting Shape of an Ion Use VSEPR theory to predict the shape of the polyatomic ion NO 3– Solution Step Draw the Lewis structure The polyatomic ion, NO3–, contains three electron groups (two single bonds between the central N atom and O atoms, and one double bond between N and O) Note that the double bond can be drawn to any of the O atoms Step Arrange the electron groups around the central atom to minimize repulsion To minimize repulsion, three electron groups would have a trigonal planar geometry Step Use the atoms bonded to the central atom to determine the shape Because NO3– has three bonded atoms, it has a trigonal planar shape Study Check 6.17 Use VSEPR theory to predict the shape of ClO2– Answer With two bonded atoms and two lone pairs of electrons, the shape of ClO2– is bent with a bond angle of 109° General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.18 Polarity of Molecules Determine whether a molecule of OF2 is polar or nonpolar Solution Step Determine if the bonds are polar covalent or nonpolar covalent From Figure 6.6, F and O have an electronegativity difference of 0.5 (4.0 – 3.5 = 0.5), which makes each of the O—F bonds polar covalent General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.18 Polarity of Molecules Continued Step If the bonds are polar covalent, draw the Lewis structure and determine if the dipoles cancel The Lewis structure for OF2 has four electron groups and two bonded atoms The molecule has a bent shape in which the dipoles of the O—F bonds not cancel The OF2 molecule would be polar Study Check 6.18 Would a PCl3 molecule be polar or nonpolar? Answer polar General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 6.19 Attractive Forces Between Particles Indicate the major type of molecular interaction—dipole–dipole attractions, hydrogen bonding, or dispersion forces— expected of each of the following: a HF b Br2 c PCl3 Solution a HF is a polar molecule that interacts with other HF molecules by hydrogen bonding b Br2 is nonpolar; only dispersion forces provide attractive forces c The polarity of the PCl3 molecules provides dipole–dipole attractions Study Check 6.19 Why is the melting point of H2S lower than that of H2O? Answer The attractive forces between H2S molecules are dipole–dipole attractions, whereas the attractive forces between H2O molecules are hydrogen bonds, which are stronger and require more energy to break General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc ... charge, and name for each resulting ion Solution Study Check 6.2 Write the symbols for the ions formed by potassium and sulfur Answer K+ and S2– General, Organic, and Biological Chemistry: Structures. .. the cation and anion Iron(III) chloride consists of a metal and a nonmetal, which means that it is an ionic compound General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake... represented by a bond line © 2016 Pearson Education, Inc General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake Sample Problem 6.12 Drawing Lewis Structures Continued