1. Chemical Bonding the chemical vessel of the tree of life

2. VOCABULARY Electronegativity: The relative attraction of an atom for a shared pair of electrons. Electronegativity: The relative attraction of an atom for a shared pair of electrons. Electron Affinity: The energy change that occurs when an electron is acquired by a neutral atom: Electron Affinity: The energy change that occurs when an electron is acquired by a neutral atom: Neutral nonmetal atom + e - → anion + Energy Neutral nonmetal atom + e - → anion + Energy Ionization Energy: The energy required to remove an electron from a neutral atom. Ionization Energy: The energy required to remove an electron from a neutral atom. Neutral metal atom + Energy → cation + e - Neutral metal atom + Energy → cation + e -

3. Vocabulary Chemical Bond: mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together. Chemical Bond: mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together. Chemical Compound: two or more elements chemically combined in the same ratio each time. Chemical Compound: two or more elements chemically combined in the same ratio each time. Chemical Formulas: shows the kinds & numbers of atoms in the smallest representative unit of the substance. Chemical Formulas: shows the kinds & numbers of atoms in the smallest representative unit of the substance.

4. What happens when atoms bond? When atoms bond, their valence electrons are redistributed. When atoms bond, their valence electrons are redistributed. The way they are redistributed determines the type of bond. The way they are redistributed determines the type of bond.

5. Three Bond Types 1. IONIC BONDING: chemical bonding that results from the electrical attraction between cations and anions.  e - transfer b/w metals & nonmetals  think salts, rocks & minerals in earth’s crust 2. COVALENT BONDING: results from the sharing of electron pairs between two atoms.  e - sharing b/w two or more nonmetals  think oceans, atmosphere, living tissue 3. METALLIC BONDING:  e - sea; all valence e - are mobile throughout  why metals are good conductors and malleable

6. Three Bond Types

7. Chemical Formulas - Ionic Formulas for ionic compounds are written such that the combined ions are in a ratio that gives neutrality. Subscripts are placed when needed. For example, magnesium ions and chloride ions combine to form one formula unit of the ionic compound magnesium chloride: Mg +2 and Cl -1 = MgCl 2 (See Ch 7)

8. Chemical Formulas - Covalent Molecular compounds are usually named using Greek prefixes to indicate the number of each type of atom present in the molecule. For example, the nonmetals nitrogen and oxygen could bond covalently to form a molecule of N 2 O 5, dinitrogen pentoxide. (See Ch 7)

9. Why do atoms bond? The Octet Rule: chemical compounds tend to form so that each atom, by gaining, losing or sharing e-, has a stable octet of electrons in its highest occupied Energy level. The Octet Rule: chemical compounds tend to form so that each atom, by gaining, losing or sharing e-, has a stable octet of electrons in its highest occupied Energy level.

10. Why do atoms bond? Changes that  PE and ↑ stability are favored in natural processes. Changes that  PE and ↑ stability are favored in natural processes. Two isolated atoms have greater PE and less stability than two bonded atoms. Two isolated atoms have greater PE and less stability than two bonded atoms. Compounds are more stable than the uncombined atoms. Compounds are more stable than the uncombined atoms. Bond formation releases Energy; spontaneous, exothermic. Bond formation releases Energy; spontaneous, exothermic. Bond breaking absorbs Energy; requires energy input, endothermic. Bond breaking absorbs Energy; requires energy input, endothermic.

11. Bond Length and Bond Energy Bond length: the distance between two bonded atoms at their MINIMUM POTENTIAL ENERGY (=maximum stability). Bond length: the distance between two bonded atoms at their MINIMUM POTENTIAL ENERGY (=maximum stability). Bond energy: the energy required to break a chemical bond and form neutral, isolated atoms. Bond energy: the energy required to break a chemical bond and form neutral, isolated atoms. Shorter bond lengths = higher bond energy. Shorter bond lengths = higher bond energy.

13. Bond Character Bonds are classified according to how the valence are distributed around the nuclei of the combining atoms. Bonds are classified according to how the valence are distributed around the nuclei of the combining atoms.

14. Polarity Non polar covalent: equal sharing Non polar covalent: equal sharing e - shared equally only if the bonding elements are identical as in the diatomic gases, or very similar, as in the hydrocarbon methane, CH 4 e - shared equally only if the bonding elements are identical as in the diatomic gases, or very similar, as in the hydrocarbon methane, CH 4 Polar covalent: unequal sharing, creates poles with partial charges Polar covalent: unequal sharing, creates poles with partial charges If atoms with different EN values form a covalent bond, the shared e - are more strongly attracted to the atom that has a higher EN. If atoms with different EN values form a covalent bond, the shared e - are more strongly attracted to the atom that has a higher EN.

15. Bond Type by Electronegativity Difference You can estimate the bond type by subtracting the difference in EN values of the bonding atoms. You can estimate the bond type by subtracting the difference in EN values of the bonding atoms. ∆EN electronegativity difference BondType ≤0.4 Non Polar Covalent Between 0.5 to 1.7 Polar Covalent ≥1.7Ionic

16. Purely Ionic Bonds Strong attractive forces b/w ions with opposite charges (cations & anions) Strong attractive forces b/w ions with opposite charges (cations & anions) Large ∆EN means valence are completely transferred from cation to anion. Large ∆EN means valence are completely transferred from cation to anion. MANY, MANY ions arrange in a pattern called a crystal lattice. MANY, MANY ions arrange in a pattern called a crystal lattice.

17. Purely Ionic Bonds Ions combine to give a neutral compound; the simplest combining ratio of the ions is the empirical formula & represents one formula unit in a large crystal lattice. Ions combine to give a neutral compound; the simplest combining ratio of the ions is the empirical formula & represents one formula unit in a large crystal lattice. A formula unit is the simplest collection of atoms from which the chemical formula can be established. A formula unit is the simplest collection of atoms from which the chemical formula can be established.

18. One representative unit of the crystal lattice = one formula unit = NaCl Crystal Lattice: the orderly arrangement of ions in an ionic compound. Crystal Lattice: the orderly arrangement of ions in an ionic compound. Lattice Energy: the energy released when one mole of an ionic compound is formed from gaseous ions. Lattice Energy: the energy released when one mole of an ionic compound is formed from gaseous ions. Lattice energy is negative when energy is released Lattice energy is negative when energy is released

19. Ionic Bonding Ions arrange in an extensive crystal lattice Ions arrange in an extensive crystal lattice One formula unit = NaCl One formula unit = NaCl

21. Properties of Ionic Substances Non-conducting, hard, brittle solids at room temperature Non-conducting, hard, brittle solids at room temperature Soluble in water Soluble in water High melting & boiling points High melting & boiling points Will conduct if molten or dissolved in water b/c ions become mobile = electrolytes: a substance that dissolves in water to give a solution that conducts electricity Will conduct if molten or dissolved in water b/c ions become mobile = electrolytes: a substance that dissolves in water to give a solution that conducts electricity

22. Why “Brittle” Means the crystal will crack or cleave when stress (like a hammer) is applied. Means the crystal will crack or cleave when stress (like a hammer) is applied. Cannot be deformed (not malleable) because the ions in lattice not free to slide over each other. Cannot be deformed (not malleable) because the ions in lattice not free to slide over each other.

23. Why Non-Conducting as a Solid? Why high melting points? The ions are rigidly trapped in the crystal lattice with very strong forces of attraction between them. The ions are rigidly trapped in the crystal lattice with very strong forces of attraction between them. The melting point of NaCl is 801°C. The melting point of NaCl is 801°C.

24. Metallic Bonding Occurs within a sample of metal atoms Occurs within a sample of metal atoms Results from the attraction between positive metal ions & the surrounding e-, which are mobile. Results from the attraction between positive metal ions & the surrounding e-, which are mobile. The valence e- are delocalized & shared by all the atoms b/c metals have vacant orbitals The valence e- are delocalized & shared by all the atoms b/c metals have vacant orbitals This arrangement is not possible in This arrangement is not possible in ionic cmpds: the e- are bound in the crystal lattice ionic cmpds: the e- are bound in the crystal lattice covalent cmpds: the e- are localized in pairs covalent cmpds: the e- are localized in pairs Highly mobile sea of electrons accounts for luster, conductivity, malleability and ductility. Highly mobile sea of electrons accounts for luster, conductivity, malleability and ductility.

25. Metallic Bonding

26. Purely Covalent Bonds → Molecular Substances Valence e - are shared in pairs b/w two or more nonmetal atoms. Valence e - are shared in pairs b/w two or more nonmetal atoms. Small or zero ∆EN means valence e - can be shared to different degrees. Small or zero ∆EN means valence e - can be shared to different degrees. Atoms arrange into individual units called molecules. Atoms arrange into individual units called molecules. Weak attractions between molecules (called intermolecular forces OR weak forces) give rise to a variety of properties. Weak attractions between molecules (called intermolecular forces OR weak forces) give rise to a variety of properties.

27. Purely Covalent Bonds → Molecular Substances Molecule: a neutral group of atoms united by covalent bonds. Molecule: a neutral group of atoms united by covalent bonds. Molecular compound: a compound whose simplest units are molecules. Molecular compound: a compound whose simplest units are molecules. Molecular formula: shows the types and numbers of atoms combined in a single molecule, using symbols and subscripts. Molecular formula: shows the types and numbers of atoms combined in a single molecule, using symbols and subscripts. Molecules can exist alone and retain all the properties of the original substance. Molecules can exist alone and retain all the properties of the original substance. The formula units in an ionic crystal cannot exist apart from the crystal lattice. The formula units in an ionic crystal cannot exist apart from the crystal lattice.

28. Covalent bonding

29. Representing Molecular (Covalent) Compounds A Lewis structure is a type of structural formula that shows the valence electrons & how they are bonding. A Lewis structure is a type of structural formula that shows the valence electrons & how they are bonding.

30. Lewis Dot Example: ICl 1. Determine the electronegativities of each 1. Determine the electronegativities of each atom and predict the bond type. atom and predict the bond type. 3.16 – 2.66 = 0.5 (polar covalent) 2. Draw the Lewis structure for each atom. 2. Draw the Lewis structure for each atom. 3. Determine the total number of valence 3. Determine the total number of valence electrons. electrons. I = 1 x 7e¯ = 7e¯ I = 1 x 7e¯ = 7e¯ Cl = 1 x 7e¯ = 7e¯ Cl = 1 x 7e¯ = 7e¯ 14e¯ 14e¯

31. 4. Arrange the atoms next to each other and connect atoms by e¯. 4. Arrange the atoms next to each other and connect atoms by e¯. - least electronegative atom in middle - if C is present, place in the middle - H is normally around the outside 5. Add e¯ to give each atom (except H, He) 5. Add e¯ to give each atom (except H, He) an octet (8e¯) an octet (8e¯) 6. Count electrons and double check against 6. Count electrons and double check against #3. #3.

32. Representing Molecular (Covalent) Compounds A molecular formula shows the types & numbers of atoms in a single molecule. A molecular formula shows the types & numbers of atoms in a single molecule. Sugar: C 6 H 12 O 6 Sugar: C 6 H 12 O 6 Carbon dioxide: CO 2 Carbon dioxide: CO 2 Peroxide: H 2 O 2 Peroxide: H 2 O 2 Ammonia: NH 3 Ammonia: NH 3

33. Molecules & their Formulas You can also write an empirical formula for a molecule You can also write an empirical formula for a molecule Empirical formulas give the simplest combining ratio of the atoms in a cmpd. Empirical formulas give the simplest combining ratio of the atoms in a cmpd. Example: Example: C 6 H 12 O 6 = CH 2 O C 6 H 12 O 6 = CH 2 O C 3 H 6 O 3 = ? C 3 H 6 O 3 = ?

34. Representing Molecular (Covalent) Compounds A structural formula shows the location of the atoms & the bonds. A structural formula shows the location of the atoms & the bonds. EX: The hydrocarbons: EX: The hydrocarbons: methane, ethane, propane, etc. methane, ethane, propane, etc. Hydrocarbon endings: Hydrocarbon endings: -ane, single bonds -ane, single bonds -ene, double bonds -ene, double bonds -yne, triple bonds -yne, triple bonds

35. Covalent Network Crystals Covalent bonding between atoms that arrange in a large crystal lattice instead of individual molecules. Covalent bonding between atoms that arrange in a large crystal lattice instead of individual molecules. Ex: Diamonds and Sand (SiO 2 ) Ex: Diamonds and Sand (SiO 2 ) Very hard substances Very hard substances

36. Seven Diatomic Molecules  A molecule containing only two atoms.  All linear & nonpolar.  Form shape of a “7” on PT  Meet Dr. Brinclhof…. H F Cl Br I ON

37. What are multiple covalent bonds?! Atoms of some elements, especially C, O & N can share more than one electron pair. Atoms of some elements, especially C, O & N can share more than one electron pair.

38. Bond Character Elements with the highest EN values are found at the upper right of the P.T. Elements with the highest EN values are found at the upper right of the P.T. A covalent bond involving these elements results in unequal sharing or polar bonds. A covalent bond involving these elements results in unequal sharing or polar bonds. H 2.1 F 4.0 Cl 3.0 Br 2.8 I 2.5 O 3.5 N 3.0 C 2.5 B 2.0 S 2.5 P 2.1

39. Polarity in molecules Non polar covalent: Even charge distribution in a molecule Non polar covalent: Even charge distribution in a molecule

40. Polarity in molecules Polar covalent: Uneven charge distribution in a molecule e - are more strongly attracted to the atom that has a higher EN. e - are more strongly attracted to the atom that has a higher EN. The result is unequal charge distribution and partial charges, or poles, on the ends of the molecule. The result is unequal charge distribution and partial charges, or poles, on the ends of the molecule.

41. Summary

42. REMEMBER There are no ions in molecules! There are no ions in molecules! Molecules can exist individually! Molecules can exist individually!AND There are no molecules in ionic crystals! There are no molecules in ionic crystals! The ions in one formula unit cannot exist apart from an extensive crystal lattice. The ions in one formula unit cannot exist apart from an extensive crystal lattice.

43. Properties of Covalent (Molecular) Compounds Weak intermolecular forces hold molecules together. Weak intermolecular forces hold molecules together. Most are gases or liquids at room temp. Most are gases or liquids at room temp. If solid, then soft. If solid, then soft. No ions in molecules so do not conduct electricity and very limited solubility in water. No ions in molecules so do not conduct electricity and very limited solubility in water. Low melting and boiling points. Low melting and boiling points. Many vaporize easily at room temp = volatile. Many vaporize easily at room temp = volatile.

44. Ionic vs Molecular PROPERTIES DEPEND ON HOW STRONGLY THE BASIC UNITS ARE ATTRACTED TO EACH OTHER! PROPERTIES DEPEND ON HOW STRONGLY THE BASIC UNITS ARE ATTRACTED TO EACH OTHER! The force of attraction between ions is quite strong – ionic crystals are hard, brittle solids with high MPts. The force of attraction between ions is quite strong – ionic crystals are hard, brittle solids with high MPts. The force of attraction between individual molecules are called weak forces – many molecular substances are gases or volatile liquids at room temp. and MPts are low. The force of attraction between individual molecules are called weak forces – many molecular substances are gases or volatile liquids at room temp. and MPts are low.

45. Ionic vs Molecular What looks like a small molecule but acts like an ion??? What looks like a small molecule but acts like an ion??? A polyatomic ion: a charged group of covalently bonded atoms A polyatomic ion: a charged group of covalently bonded atoms

46. What holds molecules together? Intermolecular Forces of Attraction

47. Intermolecular Forces Weak attractions that act between molecules. Abbreviation: IM forces AKA: Weak Forces 1. 1. Weak Forces (b/c not true chemical bonds.) 2. 2. Van Der Waals Forces after discoverer ↑ strength of IM force: ↑ BPt, MPt, surface tension, & viscosity ↓ Volatility and evaporation rate

48. Intermolecular Forces hold molecules together In order of strength: 1. 1. London Dispersion Forces: momentary attractions due to motion of nonpolar molecules 2. 2. Dipole-Dipole Forces: between polar molecules with slightly charged ends that attract each other. 3. 3. Hydrogen Bonds: Hydrogen bonded with F, O, N The reason water is liquid at room temperature!

49. London Dispersion Forces - attraction between nonpolar molecules – results from constant motion of electrons and the creation of instantaneous dipoles between nonpolar molecules

50. Intermolecular Forces – Weak forces of attraction between molecules – Weak forces of attraction between molecules Dipole – Dipole Forces Dipole – Dipole Forces – attraction between polar molecules – attraction between polar molecules – Ex. HCl, ICl – Ex. HCl, ICl Hydrogen Bonding Hydrogen Bonding – attraction between Hydrogen (+) and a strong – attraction between Hydrogen (+) and a strong electronegative atom such as F, O, N with lone pair electrons – Ex. – Ex.

52. States of Matter We can express these states of matter pictorially. Of course, the molecules are shown millions of times their actual size: We can express these states of matter pictorially. Of course, the molecules are shown millions of times their actual size:

53. Note that… Particles in a: Particles in a: gas are well separated with no regular arrangement. gas are well separated with no regular arrangement. liquid are close together with no regular arrangement. liquid are close together with no regular arrangement. solid are tightly packed, usually in a regular pattern. solid are tightly packed, usually in a regular pattern. Particles in a: Particles in a: gas vibrate and move freely at high speeds. gas vibrate and move freely at high speeds. liquid vibrate, move about, and slide past each other. liquid vibrate, move about, and slide past each other. solid vibrate (jiggle) but generally do not move from place to place. solid vibrate (jiggle) but generally do not move from place to place. Liquids and solids are often referred to as condensed phases because the particles are very close together. Liquids and solids are often referred to as condensed phases because the particles are very close together.

54. Some Characteristics of Gases, Liquids and Solids and the Microscopic Explanation for the Behavior gasliquidsolid assumes the shape and volume of its container particles can move past one another assumes the shape of the part of the container which it occupies particles can move/slide past one another retains a fixed volume and shape rigid - particles locked into place compressible lots of free space between particles not easily compressible little free space between particles flows easily particles can move past one another flows easily particles can move/slide past one another does not flow easily rigid - particles cannot move/slide past one another

55. VSEPR Theory Valence Shell Electron Pair Repulsion Theory States that: Repulsion between the sets of valence electrons surrounding an atom causes them to be oriented as far apart as possible.

56. The five most common shapes of small molecules 1. 1. Linear 2. 2. Trigonal Planar 3. 3. Tetrahedral 4. 4. Trigonal Pyramidal 5. 5. Bent 6. 6. Trigonal Bipyramidal 7. 7. Octahedral

57. Molecular Geometry The shape of molecules affects the physical & chemical properties of molecular (covalent) substances. All molecules have a symmetrical shape because the bonds & atoms are arranged with equal distances separating atoms that are NOT bonded to each other. WHY? A repulsive force exists between e - pairs in molecules.

58. How do molecules get their shapes? Valence e - surrounding an atom may be shared in pairs OR left unshared. Both bonded and unbonded e - pairs will repel each other – LIKE CHARGES REPEL. Unshared e - pairs repel each other VERY STRONGLY!!!

59. Molecular Geometry Common Molecular Shapes Linear: The atoms of a linear molecule are connected in a straight line. *2 or 3 atom molecules! Linear: The atoms of a linear molecule are connected in a straight line. *2 or 3 atom molecules! All 2 atom molecules are linear (O 2, HCl). Many 3 atom molecules are also linear. (CO 2 ) 6-26

60. Hybrid Orbitals – form when s & p orbitals mix, creating symmetry around the central atom in a molecule

61. Molecular Geometry Common Molecular Shapes Linear: Linear: All 2 atom molecules are linear (O 2, HCl). Many 3 atom molecules are also linear. (CO 2 ) 6-26

62. Molecular Geometry Trigonal Planar: Molecules have a triangular, bent shape. Trigonal Planar: Molecules have a triangular, bent shape. *4 atom molecules A central atom Ex. BCl 3 bonded to 3 other atoms. A central atom Ex. BCl 3 bonded to 3 other atoms.6-28

63. Molecular Geometry Trigonal Planar: Trigonal Planar:

64. Molecular Geometry Tetrahedral: Tetrahedral:

65. Molecular Geometry Tetrahedral: A shape that has four surfaces. Tetrahedral: A shape that has four surfaces. *5 atom molecules. Tripod shaped. Ex. CH 4 All four sides are Ex. CH 4 All four sides areidentical.6-29

66. Molecular Geometry Trigonal Pyramidal: The molecule has a central atom that is bonded to three other atoms and has an unshared pair of valence electrons. Trigonal Pyramidal: The molecule has a central atom that is bonded to three other atoms and has an unshared pair of valence electrons. *4 atom molecules Ex. NH 3

67. Molecular Geometry Trigonal Pyramidal: Trigonal Pyramidal:

68. Molecular Geometry Bent: Bent:

69. Molecular Geometry Bent: 2 unshared pairs result in a slightly smaller bond angle, due to an even greater repulsion force. Bent: 2 unshared pairs result in a slightly smaller bond angle, due to an even greater repulsion force. *3 atom molecules Ex. H 2 O

70. Hybrid Orbitals When an atom approaches another atom to form a bond, its orbitals may be changed to new, equal-energy orbitals. When an atom approaches another atom to form a bond, its orbitals may be changed to new, equal-energy orbitals. When s and p orbitals mix, they form new patterns, like waves in water. When s and p orbitals mix, they form new patterns, like waves in water.

71. Polarity of Molecules Remember, individual covalent bonds can be polar or nonpolar. Molecules as a whole can also be polar or nonpolar. Polar Molecule: A molecule whose charge distribution is NOT symmetrical. Dipole: A dipole is a polar molecule.

72. Determining the Polarity of a Molecule To determine whether a molecule is polar or nonpolar, you must examine the following: 1. 1. The polarity of its bonds (use ∆ EN) 2. 2. The shape of the molecule. 3. 3. The presence of unshared e - pairs.

73. Determining the Polarity of a Molecule The rule of thumb is: If the charge is symmetrical around the central atom = nonpolar molecule. If the charge is not symmetrical around the central atom = polar molecule.

74. Bond Length Atoms farther down a group on the P.T. form longer bonds b/c the atoms are larger down a group. Multiple bonds are shorter than single bonds b/c more e - are present to attract positive nuclei.

75. Large Molecules Many large molecules, macromolecules, are essential to living organisms. EX: proteins and DNA Many have both polar and non- polar ends that give them a complex, 3-D shape that allows them to serve their specialized functions.

76. Wonderful Water Most three atom molecules are linear, nonpolar gases at room temp. b/c there are no attractive forces between them. Water is a very polar molecule with a bent shape. Water has very strong IM forces due to its shape, polarity and H- bonding so it is a liquid at room temperature!

77. Representing Molecules H 2 O H 2 O BeF 2 BeF 2 CH 4 CH 4

78. Lewis Structures are used to represent bonding

79. The water molecule has a bent shape and is very polar

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