Ionic and Molecular Compounds

Transcription

1 Ionic and Molecular Compounds Chapter 6 Ch. 6 Ionic and Molecular Compounds 6.1 Ions: Transfer of Electrons 6.2 Writing Formulas for Ionic Compounds 6.3 Naming and Writing Ionic Formulas 6.4 Polyatomic Ions 6.5 Molecular Compounds: Sharing Electrons 6.6 Lewis Structures for Molecules and Polyatomic Ions 6.7 Electronegativity and Bond Polarity 6.8 Shapes and Polarity of Molecules 6.9 Attractive Forces in Compounds

2 6.1 Ions: Transfer of Electrons Learning Goal Write the symbols for the simple ions of the representative elements. Ionic and Covalent Bonds Chemical bonds are formed when atoms lose, gain, or share valence electrons to completely fill their outermost electron shell. Ionic bonds occur when valence electrons of a metal atom are transferred to the atom of a nonmetal. Covalent bonds occur when nonmetal atoms share electrons to attain a noble gas arrangement.

3 Ionic and Covalent Bonds Positive Ions: Metals Lose Electrons In ionic bonding, ions form when atoms gain or lose their valence electrons to form a stable electron configuration. Metals: have low ionization energies. readily lose one or more of their valence electrons to form ions with a positive charge. lose electrons until they have the same number of valence electrons as the nearest noble gas, usually eight valence electrons.

4 Positive Ions: Loss of Electrons When sodium atoms in Group 1 are neutral, they have 11 electrons and 11 protons. They lose one electron to have the same number of valence electrons as neon and a filled energy level. They will form an ion with 10 electrons, 11 protons, and an ionic charge of 1+: Na +. Positive Ions: Loss of Electrons When magnesium atoms in Group 2 are neutral, they have 12 electrons and 12 protons. They will lose 2 electrons to have the same number of valence electrons as neon and a filled energy level. They form an ion with 10 electrons, 12 protons, with an ionic charge of 2+: Mg 2+.

5 Negative Ions: Nonmetals Gain Electrons Nonmetals Have high ionization energies readily gain one or more valence electrons to form ions with a negative charge. gain electrons until they have the same number of valence electrons as the nearest noble gas, usually eight valence electrons. Negative Ions: Gain of Electrons When chlorine atoms in Group 17 are neutral, they have 17 electrons and 17 protons. They will gain one electron to have the same number of valence electrons as argon. They form an ion with 18 electrons, 17 protons, and a charge of 1 : Cl.

6 Formulas, Names of Common Ions Ionic Charges, Group Numbers We can use the group numbers in the periodic table to determine the charges for the ions.

7 Chemistry Link to Health: Important Ions in the Body Ions are important in regulating body functions. Ion Occurrence Function Source Na + K + Ca 2+ Mg 2+ Principal cation outside the cell Principal cation outside the cell Cation outside the cell; found in bones Cation outside the cell; found in bones Regulation and control of body fluids Regulation of body fluids and cellular functions Major cation in bones, needed for muscle contractions Essential for certain enzymes, muscles, and nerve control Salt, cheese, pickles Bananas, potatoes, orange juice, milk Milk, yogurt, cheese, greens, spinach Chlorophyll, nuts, grains Study Check Write the formula and symbol of an ion with 16 protons and 18 electrons.

8 Study Check Consider the elements calcium and chlorine. 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 acquire an octet. D. Write the symbol, including its ionic charge, and name of each resulting ion. Ch. 6 Ionic and Molecular Compounds 6.1 Ions: Transfer of Electrons 6.2 Writing Formulas for Ionic Compounds 6.3 Naming and Writing Ionic Formulas 6.4 Polyatomic Ions 6.5 Molecular Compounds: Sharing Electrons 6.6 Lewis Structures for Molecules and Polyatomic Ions 6.7 Electronegativity and Bond Polarity 6.8 Shapes and Polarity of Molecules 6.9 Attractive Forces in Compounds

9 6.2 Writing Formulas for Ionic Compounds Learning Goal Using charge balance, write the correct formula for an ionic compound. Properties of Ionic Compounds Ionic compounds consist of positive and negative ions. have attractions called ionic bonds between positively and negatively charged ions. have high melting points. are solids at room temperature.

10 NaCl, An Ionic Compound Sodium chloride is more commonly known as table salt. The magnification of NaCl crystals shows the arrangement of Na + and Cl ions in an NaCl crystal. Formulas of Ionic Compounds In a chemical formula, the symbols and subscripts are written in the lowest whole-number ratio of the atoms or ions. the sum of ion charges equals zero. the total positive charge = total negative charge.

11 Subscripts in Formulas Writing Ionic Formulas from Ion Charges To balance ionic charge in an ionic compound, total positive charge = total negative charge

12 Study Check Write the ionic formula of the compound formed with Ba 2+ and Cl ions. Study Check Select the correct formula for each of the following ionic compounds. 1. Na + and O 2 A. NaO B. Na 2 O C. NaO 2 2. Al 3+ and Cl A. AlCl 3 B. AlCl C. Al 3 Cl 3. Mg 2+ and N 3 A. MgN B. Mg 2 N 3 C. Mg 3 N 2

13 Ch. 6 Ionic and Molecular Compounds 6.1 Ions: Transfer of Electrons 6.2 Writing Formulas for Ionic Compounds 6.3 Naming and Writing Ionic Formulas 6.4 Polyatomic Ions 6.5 Molecular Compounds: Sharing Electrons 6.6 Lewis Structures for Molecules and Polyatomic Ions 6.7 Electronegativity and Bond Polarity 6.8 Shapes and Polarity of Molecules 6.9 Attractive Forces in Compounds 6.3 Naming and Writing Ionic Compounds Learning Goal Given the formula of an ionic compound, write the correct name; given the name of an ionic compound, write the correct formula.

14 Naming Ionic Compounds When naming an ionic compound, the name of the metal is written first and is the same as the name of the element. the name of the nonmetal is the first syllable of the nonmetal name + ide ending and is written second. a space is placed between the name of the metal and nonmetal ion. Names of Some Ionic Compounds

15 Naming Ionic Compounds, K 2 O Name the ionic compound K 2 O. Study Check Write the names of the following compounds. A. CaO B. Al 2 O 3 C. MgCl 2

16 Metals with Variable Charge Transition metals except for Zn 2+, Cd 2+, and Ag + form two or more positive ions (cations). A Roman numeral equal to the ion charge is placed in parentheses immediately after the metal name. Cu 2+ copper(ii) Pb 2+ lead(ii) Cu + copper(i) Pb 4+ lead(iv) Fe 2+ iron(ii) Cr 2+ chromium(ii) Fe 3+ iron(iii) Cr 3+ chromium(iii) Metals with Variable Charge

17 Determination of Variable Charge Determine the charge of the metal ion in: MnF 2 Ion Charges, Periodic Table

18 Naming Ionic Compounds with Variable Charge Metals, FeCl 2 Name the ionic compound FeCl 2. Study Check Name the following ionic compound containing a variable charge metal. SnO 2

19 Writing Formulas from the Name of an Ionic Compound The formula for an ionic compound is written from, the first part of the name that describes the metal ion. the second part of the name that specifies the nonmetal ion. Subscripts are added to balance the charge. Writing Formulas from the Name of an Ionic Compound Write the formula for iron(iii) chloride.

20 Study Check Write chemical formulas for the following compounds: A. nickel(ii) sulfide B. aluminum chloride C. iron(iii) oxide Ch. 6 Ionic and Molecular Compounds 6.1 Ions: Transfer of Electrons 6.2 Writing Formulas for Ionic Compounds 6.3 Naming and Writing Ionic Formulas 6.4 Polyatomic Ions 6.5 Molecular Compounds: Sharing Electrons 6.6 Lewis Structures for Molecules and Polyatomic Ions 6.7 Electronegativity and Bond Polarity 6.8 Shapes and Polarity of Molecules 6.9 Attractive Forces in Compounds

21 6.4 Polyatomic Ions Learning Goal Write the name and formula for an ionic compound containing a polyatomic ion. Polyatomic Ions An ionic compound may contain a polyatomic ion (many-atom ion) as one its cations or anions. A polyatomic ion is a group of covalently bonded atoms that has an overall ionic charge. Most polyatomic ions are made up of nonmetals (SO, NO, ClO ) Almost all of them have negative charges (-1, -2, -3, etc) NH

22 Polyatomic Ions Polyatomic Ions, Names, and Formulas

23 Names of Polyatomic Ions 1. Names of polyatomic ions end in ate. SO 2 4 sulfate PO 3 4 phosphate NO 3 nitrate 2. When a related ion has one less oxygen, its name ends in ite. SO 2 3 sulfite PO 3 3 phosphite NO 2 nitrite Names of Polyatomic Ions 3. Exceptions to these rules are the following: CN cyanide OH hydroxide 4. Halogens form 4 polyatomic ions with oxygen. Each has a 1 charge. ClO 4 perchlorate ClO 3 chlorate ClO 2 chlorite ClO hypochlorite

24 Writing Formulas for Compounds Containing Polyatomic Ions When writing formulas for ionic compounds containing polyatomic ions, we use the same rules of charge balance as those for simple ionic compounds. Magnesium nitrate Writing Formulas with Polyatomic Ions Write the formula for aluminum nitrite

25 Study Check Write the formula for sodium phosphate. Naming Compounds with Polyatomic Ions When naming ionic compounds containing polyatomic ions, first write the positive ion, usually a metal. write the name of the polyatomic ion second. Recognizing polyatomic ions in a chemical formula helps to name it correctly.

26 Compounds with Polyatomic Ions Study Check Select the correct formula for each. 1. aluminum nitrate A. AlNO 3 B. Al(NO) 3 C. Al(NO 3 ) 3 2. copper(ii) nitrate A. CuNO 3 B. Cu(NO 3 ) 2 C. Cu 2 (NO 3 )

27 Study Check Select the correct formula for each. 3. iron(iii) hydroxide A. FeOH B. Fe 3 OH C. Fe(OH) 3 4. tin(iv) hydroxide A. Sn(OH) 4 B. Sn(OH) 2 C. Sn 4 (OH) Flow Chart, Naming Ionic Compounds

28 Study Check Name the following ionic compounds: A. Ca(NO 3 ) 2 B. FePO 4 Study Check Name each of the following compounds containing polyatomic ions. A. MgSO 3 B. MgSO 4 C. Pb 3 (PO 3 ) 2

29 Study Check Name each of the following compounds: A. Fe 2 (SO 4 ) 3 B. Ba 3 (PO 3 ) 2 C. NiCO 3 Ch. 6 Ionic and Molecular Compounds 6.1 Ions: Transfer of Electrons 6.2 Writing Formulas for Ionic Compounds 6.3 Naming and Writing Ionic Formulas 6.4 Polyatomic Ions 6.5 Molecular Compounds: Sharing Electrons 6.6 Lewis Structures for Molecules and Polyatomic Ions 6.7 Electronegativity and Bond Polarity 6.8 Shapes and Polarity of Molecules 6.9 Attractive Forces in Compounds

30 6.5 Molecular Compounds: Sharing Electrons Learning Goal Given the formula of a molecular compound, write its correct name; given the name of a molecular compound, write its formula. Covalent Bonds Molecular compounds form when atoms of two or more nonmetals share electrons and form a covalent bond. valence electrons are shared by nonmetal atoms to achieve stability. A molecule forms when two or more atoms share electrons.

31 Names and Formulas, Molecular Compounds When naming a molecular compound, the first nonmetal in the formula is named by its element name. second nonmetal is named using the first syllable of the name followed by ide. When a subscript indicates two or more atoms of an element, a prefix is shown in front of its name. Names and Formulas, Molecular Compounds Several compounds may be formed from the same two nonmetals: CO 2 = carbon dioxide CO = carbon monoxide The number of oxygen atoms present is indicated by the prefix. When the vowels o and o or a and o appear together, the first vowel is omitted. NO = nitrogen monoxide,

32 Common Molecular Compounds Naming Molecular Compounds, NCl 3 Name the molecular compound NCl 3.

33 Study Check Name the molecular compound B 2 O 3. Study Check Write the molecular formula for diphosphorus pentoxide.

34 Compounds, Ionic or Covalent? A compound is ionic if a metal and a nonmetal are bound together OR the compound begins with K 2 O: potassium oxide NH 4 NO 3 : ammonium nitrate A compound is covalent if 2+ nonmetals are bound together. N 2 O: dinitrogen oxide Flowchart, Naming Compounds

35 Study Check Select the correct name for each compound. 1. SiCl 4 A. silicon chloride B. tetrasilicon chloride C. silicon tetrachloride 2. P 2 O 5 A. phosphorus oxide B. phosphorus pentoxide C. diphosphorus pentoxide 3. Cl 2 O 7 A dichlorine heptoxide B. dichlorine oxide C. chlorine heptoxide Study Check Identify each compound as ionic or covalent and give its correct name. A. SO 3 B. BaCl 2 C. (NH 4 ) 3 PO 3 D. Cu 2 CO 3 E. N 2 O 4

36 Ch. 6 Ionic and Molecular Compounds 6.1 Ions: Transfer of Electrons 6.2 Writing Formulas for Ionic Compounds 6.3 Naming and Writing Ionic Formulas 6.4 Polyatomic Ions 6.5 Molecular Compounds: Sharing Electrons 6.6 Lewis Structures for Molecules and Polyatomic Ions 6.7 Electronegativity and Bond Polarity 6.8 Shapes and Polarity of Molecules 6.9 Attractive Forces in Compounds 6.6 Lewis Structures for Molecules and Polyatomic Ions Learning Goal: Draw the Lewis structures for molecular compounds or polyatomic ions.

37 The Simplest Molecule, H 2 When two H atoms are far apart, they feel no attraction or repulsion to each other. As they approach each other, the electron on one H is attracted to the proton (nucleus) of the other. And vice versa. The attraction is stronger than the repulsion between the two electrons. A covalent bond forms from each H sharing its electron with the other, creating the molecule: H 2. Each H acts as if it has 2 electrons. This gives it the electron configuration of He and therefore is very stable. The Octet Rule Atoms are the most stable when they have the electron configuration of a noble gas. For H and He, that s 2 electrons For n=2 and n=3 (Li through Ar) that is 8 electrons (n=4 etc is higher. We won t worry about that now.) The Octet Rule: Most atoms want to have 8 valence electrons. Exceptions: H, He (2 valence electrons) B (can only have 6) n=3 can have more than 8 due to access to the 3d orbital.

38 Lewis Structures, Molecules A molecule is represented by a Lewis structure in which the valence electrons of all the atoms are arranged to give octets. The shared electrons, or bonding pairs, are shown as two dots or a single line between atoms. The nonbonding pairs, or lone pairs, are placed on the outside of the atoms. Lewis Structures, Molecules A molecule is represented by a Lewis structure in which the valence electrons of all the atoms are arranged to give octets.

39 Elements, Diatomic Molecules The elements hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine exist as diatomic molecules. Number of bonds The number of electrons a nonmetal atom shares and the number of covalent bonds it forms are equal to the number of electrons it needs to achieve a stable electron configuration. # of bonds = 8 number of valence e s

40 Guide to Drawing Lewis Structures 1. Sum the valance electrons from all the atoms. 2. Decide on atom connections and connect with a single bond. ( central atom is usually written first in the formula.) 3. Determine the number of valence electrons remaining Total valence electrons (step 1) minus # electrons used in bonding. 4. Complete the octets of terminal atoms (except H and He want 2) 5. Place leftover electrons on the central atom. 6. If no unassigned electrons remain, and the central atom doesn t have an octet, use multiple bonds. Drawing Lewis Structures Draw the Lewis structure for methane, CH 4 1. Sum the valance electrons from all the atoms. 2. Decide on atom connections and connect with a single bond. ( central atom is usually written first in the formula.) 3. Determine the number of valence electrons remaining Total valence electrons (step 1) minus # electrons used in bonding. 4. Complete the octets of terminal atoms (except H and He want 2) 5. Place leftover electrons on the central atom. 6. If no unassigned electrons remain, and the central atom doesn t have an octet, use multiple bonds.

41 Molecules, Lewis Structures Study Check Draw the Lewis structure for NH Sum the valance electrons from all the atoms. 2. Decide on atom connections and connect with a single bond. ( central atom is usually written first in the formula.) 3. Determine the number of valence electrons remaining Total valence electrons (step 1) minus # electrons used in bonding. 4. Complete the octets of terminal atoms (except H and He want 2) 5. Place leftover electrons on the central atom. 6. If no unassigned electrons remain, and the central atom doesn t have an octet, use multiple bonds.

42 Study Check Draw the Lewis structure for BF 3 1. Sum the valance electrons from all the atoms. 2. Decide on atom connections and connect with a single bond. ( central atom is usually written first in the formula.) 3. Determine the number of valence electrons remaining Total valence electrons (step 1) minus # electrons used in bonding. 4. Complete the octets of terminal atoms (except H and He want 2) 5. Place leftover electrons on the central atom. 6. If no unassigned electrons remain, and the central atom doesn t have an octet, use multiple bonds. Double and Triple Bonds A double bond occurs when atoms share two pairs of electrons. forms when there are not enough electrons to complete octets. A triple bond occurs when atoms share three pairs of electrons. forms when there are not enough electrons to complete octets.

43 Study Check Draw the Lewis structure for N Sum the valance electrons from all the atoms. 2. Decide on atom connections and connect with a single bond. ( central atom is usually written first in the formula.) 3. Determine the number of valence electrons remaining Total valence electrons (step 1) minus # electrons used in bonding. 4. Complete the octets of terminal atoms (except H and He want 2) 5. Place leftover electrons on the central atom. 6. If no unassigned electrons remain, and the central atom doesn t have an octet, use multiple bonds. Study Check Draw the Lewis structure for HCN. 1. Sum the valance electrons from all the atoms. 2. Decide on atom connections and connect with a single bond. ( central atom is usually written first in the formula.) 3. Determine the number of valence electrons remaining Total valence electrons (step 1) minus # electrons used in bonding. 4. Complete the octets of terminal atoms (except H and He want 2) 5. Place leftover electrons on the central atom. 6. If no unassigned electrons remain, and the central atom doesn t have an octet, use multiple bonds.

44 Ch. 6 Ionic and Molecular Compounds 6.1 Ions: Transfer of Electrons 6.2 Writing Formulas for Ionic Compounds 6.3 Naming and Writing Ionic Formulas 6.4 Polyatomic Ions 6.5 Molecular Compounds: Sharing Electrons 6.6 Lewis Structures for Molecules and Polyatomic Ions 6.7 Electronegativity and Bond Polarity 6.8 Shapes and Polarity of Molecules 6.9 Attractive Forces in Compounds 6.7 Electronegativity and Bond Polarity Learning Goal: Use electronegativity to determine the polarity of a bond.

45 Electronegativity The electronegativity of an atom is its ability to attract the shared electrons in a bond. Electronegativity When the atoms in the bond are different, the more electronegative atom will hog the shared electrons in the covalent bond. The electrons will spend more time near the more electronegative atom.

46 Polarity of Bonds Differences in electronegativity of atoms dictate what kind of bond forms between the atoms. ΔEN = 0 a nonpolar covalent bond ΔEN = between 0 and 2 a polar covalent bond ΔEN 2 an ionic bond Nonpolar Covalent Bonds A nonpolar covalent bond occurs between nonmetals. It is an equal sharing of electrons by the two bonding atoms. ΔEN = 0 a nonpolar covalent General, Organic, bondand Biological Chemistry: Structures of Life, 5/e ΔEN = between 0 and 2 a polar covalent bond b d

47 Polar Covalent Bonds A polar covalent bond occurs between nonmetal atoms. It is an unequal sharing of electrons. has a moderate electronegativity difference. Electronegativity Atoms Difference Type of Bond O-Cl = 0.5 Polar covalent Cl-C = 0.5 Polar covalent O-S = 1.0 Polar covalent ΔEN = 0 a nonpolar covalent General, Organic, bondand Biological Chemistry: Structures of Life, 5/e ΔEN = between 0 and 2 a polar covalent bond b d Dipoles and Bond Polarity A polar covalent bond becomes more polar as the difference in electronegativity increases. The separation of charges in a polar bond is called a dipole. The positive and negative ends of the dipole are located by using the lowercase Greek letter delta with a positive or negative charge. an arrow that points from the positive to the negative end of the dipole.

48 Ionic Bonds An ionic bond occurs between metal and nonmetal ions. is a result of electron transfer. has a large electronegativity difference (2.0 or more). Electronegativity Atoms Difference Type of Bond Cl-K = 2.2 Ionic N-Na = 2.1 Ionic ΔEN = 0 a nonpolar covalent General, Organic, bondand Biological Chemistry: Structures of Life, 5/e ΔEN = between 0 and 2 a polar covalent bond b d Electronegativity and Bond Types ΔEN = 0 ΔEN = 0 to 2 ΔEN = 2+

49 Study Check Use the electronegativity difference to identify the type of bond (nonpolar covalent [NP], polar covalent [P], or ionic [I]) between the following: A. K N B. N O C. Cl Cl D. H Cl Ch. 6 Ionic and Molecular Compounds 6.1 Ions: Transfer of Electrons 6.2 Writing Formulas for Ionic Compounds 6.3 Naming and Writing Ionic Formulas 6.4 Polyatomic Ions 6.5 Molecular Compounds: Sharing Electrons 6.6 Lewis Structures for Molecules and Polyatomic Ions 6.7 Electronegativity and Bond Polarity 6.8 Shapes and Polarity of Molecules 6.9 Attractive Forces in Compounds

50 6.8 Shapes and Polarity of Molecules Learning Goal: Predict the three-dimensional structure of a molecule, and classify it as polar or nonpolar. VSEPR Theory Valence Shell Electron-Pair Repulsion Theory (VSEPR) describes the orientation of electron groups around the central atom. states that electron groups are arranged as far apart as possible around the central atom. states that the specific shape of a molecule is determined by the number of atoms attached to the central atom.

51 Linear (2 bond locations) In a molecule of CO 2 two electron groups are placed around the central atom, carbon. the repulsion is minimized by placing the two groups on opposite sides of the carbon atom, giving this a linear arrangement with bond angles of 180. the shape with two electron groups around the central atom is linear. Triganol Planar (3 bond locations) In a molecule of formaldehyde, H 2 CO 3, three electron groups are placed around the central atom, carbon. the repulsion is minimized by placing the three groups as far apart as possible at bond angles of 120. the shape with three electron groups around the central atom is trigonal planar.

52 Bent (2 bond locals + 1 electron pair) In a molecule of SO 2, there are three electron groups around the central atom S: The repulsion is minimized by placing the three electron groups as far apart as possible. The shape with two bonds and a lone pair on the central atom is bent with a bond angle of 120. Tetrahedral (4 bond locations) In a molecule of CH 4 four electron groups are attached to H atoms around the central atom, carbon. the repulsion is minimized by placing the four electron groups at corners of a tetrahedron with bond angles of 109. the shape with four bonds on the central atom is called tetrahedral.

53 Trigonal Pyrimidal (3 bond locals + 1 electron pair) In a molecule of NH 3 four electron groups, three bonds to H atoms and one lone pair, are around the central atom, N. the repulsion is minimized by placing the four electron groups at corners of a tetrahedron with bond angles of 109. the shape with three bonds and a lone pair on the central atom is called trigonal pyrimidal. Bent (type 2) (2 bond locals + 2 e- pairs) In a molecule of H 2 O four electron groups, two bonds to H atoms and two lone pairs, are around the central atom, O. the repulsion is minimized by placing the four electron groups at corners of a tetrahedron with bond angles of 109. the shape with two bonds and two lone pairs on the central atom is called bent.

54 Molecular Shapes, Electron-Groups Guide to Predicting Molecular Shape 1. Draw the Lewis structure. 2. Determine electron-group geometry based on total number of electron locations on the central atom. (bonds and electron pairs) Single, double, triple bond all equal one electron location Every electron pair equals one electron location. 3. Determine the molecular shape based on how many ATOMS are bonded to the central atom.

55 Predicting molecular shapes Predict the shape of a molecule of H 2 S. Study Check State the number of electron groups and lone pairs and use VSEPR theory to determine the shape of the following molecules or ions as tetrahedral, trigonal pyramidal, or bent. A. PF 3 B. H 2 O C. CCl 4

56 Polarity of Molecules Nonpolar molecules such as H 2, Cl 2, and O 2 are nonpolar because they contain nonpolar bonds. Polar bonds can be nonpolar if the polar bonds (dipoles) cancel in a symmetrical arrangement, such as in CO 2 and CF 4.

57 Polarity of Molecules Polar molecules such as HCl are polar because one end of the molecule is more negatively charged than the other. the polar bonds in the molecule do not cancel each other. the electrons are shared unequally in the polar covalent bond. In a polar molecule such as H 2 O, there are two lone pairs and two bonds around the central atom. are dipoles that do not cancel since the shape is bent, making the molecule positive at one end and negative at the other end. is a partial negative charge on the central atom.

58 Polarity of Molecules In a polar molecule such as NH 3, there is one lone pair and three bonds around the central atom. are dipoles that do not cancel since the shape is trigonal pyramidal, making the molecule positive at one end and negative at the other end. is a partial negative charge on the central atom. Guide to Determining the Polarity of a Molecule

59 Determination of Polarity Determine if the molecule OF 2 is polar or nonpolar. Study Check Identify each of the following molecules as polar or nonpolar. A. PBr 3 B. HBr C. CH 4

60 Ch. 6 Ionic and Molecular Compounds 6.1 Ions: Transfer of Electrons 6.2 Writing Formulas for Ionic Compounds 6.3 Naming and Writing Ionic Formulas 6.4 Polyatomic Ions 6.5 Molecular Compounds: Sharing Electrons 6.6 Lewis Structures for Molecules and Polyatomic Ions 6.7 Electronegativity and Bond Polarity 6.8 Shapes and Polarity of Molecules 6.9 Attractive Forces in Compounds 6.9 Attractive Forces in Compounds Learning Goal: Describe the attractive forces between ionic compounds, polar covalent molecules, and nonpolar covalent molecules.

61 Attractive Forces Intramolecular forces: attractive forces between atoms within compounds Polar covalent bonds Nonpolar covalent bonds Ionic bonds Intermolecular forces: attractive forces between different molecules. London dispersion forces Dipole-dipole interactions Hydrogen bonds London dispersion Forces London dispersion forces are weak attractions between nonpolar molecules. caused by temporary dipoles that develop when molecules bump into each other. weak but make it possible for nonpolar molecules to form liquids and solids.

62 Dipole-dipole interactions Dipole-dipole interactions are Attractions between polar molecules. Hydrogen Bonds Hydrogen bonds are the strongest intermolecular attraction. occur between hydrogen atoms bonded to F, O, or N, and a lone pair on F, O, or N.

63 Comparison of Bonding and Attractive Forces Melting Points and Attractive Forces Melting points of compounds are related to the strength of attractive forces between molecules or compounds. are lower due to weak forces such as dispersion forces. are higher due to stronger attractive forces such as hydrogen bonding. are highest in ionic compounds due to the strong attractive forces between ions in the compound.

64 Melting Points and Attractive Forces Study Check Identify the main type of attractive forces that are present in liquids of the following compounds: ionic bonds, dipole-dipole, hydrogen bonds, or London dispersion forces. A. NCl 3 B. H 2 O London dispersion nonpolar molecules Dipole-dipole between 2 polar molecules Hydrogen bond X-H --- X (X=N, O, or F) Ionic Bond metal and nonmetal

65 Study Check Identify the main type of attractive forces that are present in liquids of the following compounds: ionic bonds, dipole-dipole, hydrogen bonds, or London dispersion forces. C. Br-Br D. KCl E. NH 3 London dispersion nonpolar molecules Dipole-dipole between 2 polar molecules Hydrogen bond X-H --- X (X=N, O, or F) Ionic Bond metal and nonmetal Ch. 6 Ionic and Molecular Compounds 6.1 Ions: Transfer of Electrons 6.2 Writing Formulas for Ionic Compounds 6.3 Naming and Writing Ionic Formulas 6.4 Polyatomic Ions 6.5 Molecular Compounds: Sharing Electrons 6.6 Lewis Structures for Molecules and Polyatomic Ions 6.7 Electronegativity and Bond Polarity 6.8 Shapes and Polarity of Molecules 6.9 Attractive Forces in Compounds

66 Concept Map