Slide 1 / 186 Slide 2 / 186 Covalent Bonding Note: Students and classrooms with iPads should download the free "Lewis Dots" App and can use that on all the slides where Lewis Dot drawings are to be done. Slide 3 / 186 Slide 4 / 186 Table of Contents: Covalent Bonding Click on the topic to go to that section Covalent versus Ionic Bonds · Covalent versus Ionic Bonds · Properties of Ionic and Covalent Materials · Naming Binary Molecular Compounds · Lewis Structures · Resonance Structures · VSEPR Theory · Molecular Geometry Return to Table of · Polarity Contents Slide 5 / 186 Slide 6 / 186 Covalent Bonding & Molecular Geometry Covalent Bonding & Molecular Geometry Examine these two forms of the This form of ibuprofen is about This form of ibuprofen same compound, ibuprofen. 100x more effective at has virtually no alleviating pain anti-inflammatory effect. than the other form. Even though they consist of the exact same number and kinds of atoms, these two molecules have very different chemical properties.
Slide 7 / 186 Slide 8 / 186 Chemical Bonds Covalent Bonding & Molecular Geometry Chemical bonds hold atoms together to create chemical compounds. There are three basic types of bonds: Take a look around you. Ionic - The electrostatic attraction between ions The chemistry of everything you see, hear, feel, touch and taste is a result of not only Covalent - The sharing of electrons what it's made of but also how between atoms it's put together. (Remember this for next year in biology!) Metallic - Each metal atom bonds to other metals atoms within a "sea" of In this unit, we will explore what causes molecules to have electrons (covered in a later unit) various shapes. Later, we will then examine how molecular geometry affects different chemical properties. Slide 9 / 186 Slide 10 / 186 Chemical Bonds Chemical Bonds How ionic or covalent a bond is depends on the difference in We can make a few simplifications... electronegativity. The smaller the difference, the more likely electrons are "shared" and the bond is considered covalent, the greater the Ionic Bonding difference, the more likely electrons have been transferred and the Ionic bonds occur when the difference in electronegativity between atoms are ionized resulting in an ionic bond. two atoms is more than 1.7. Na ---- F electronegativity = 3 Li Be B C N O F Covalent Bonding If the difference of electronegativity is less than 1.7, neither atom Electronegativity 1.0 1.6 2.0 2.5 3.0 3.5 4.0 takes electrons from the other; they share electrons. This type of bonding Bond Li-F Be-F B-F C-F N-F O-O F-F typically takes place between two non-metals or between two metals. Electronegativity 3 2.4 2.0 1.5 1 0.5 0 H ---- Cl electronegativity = 1.1 Increasing Covalent Character Slide 11 / 186 Slide 12 / 186 Ionic v. Covalent Bonding In the case of ionic bonding, a 3-D lattice of ions is the result . . . not individual molecules. The chemical formula for an ionic compound is just the ratio of each type of ion in the lattice, not a particular number of ions in a molecule. In contrast, covalent bonding can result in individual molecules or 3-D lattices depending on the elements involved. The bonding and the shapes of these molecules help click here for an animation about ionic and covalent bonding determine the physical and chemical properties of everything around us!
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Slide 15 (Answer) / 186 Slide 16 / 186 Properties of Ionic and Covalent Materials Return to Table of Contents Slide 17 / 186 Slide 18 / 186 Properties of Ionic Compounds Properties of Ionic Compounds Conductivity Boiling and Melting Points Since the attractions between the ions span a short distance, Since ionic compounds consist of ions, when these ions these forces are quite strong resulting in high melting points and are free to move, the substance can conduct electricity. boiling points! To move, they must be in the liquid or molten state. Na+ -- Cl- + + it takes a lot of energy to break - - - an ionic lattice! + - + + - Compound Melting Point (C) NaCl (s) Molten NaCl(l) NaCl 801 Lattice is strong, no conductivity Lattice is broken, ions are free MgO 2852 to move and conduct Slide 19 / 186 Slide 20 / 186 Properties of Metallic Substances REAL WORLD APPLICATION Melting and Boiling Points In order to obtain pure metals, the ancients had to melt the metal (metallic substance) out of the rock (an ionic compound). Metallic compounds are held together by non-directional covalent bonds in which some electrons are shared but are loosely held and free to roam. The covalent bonds between the metal atoms are strong! This Why do you think the gives rise to high melting and boiling points! bronze age (copper mixed with tin) came before the strong metallic covalent bonds iron age? Metallic Lattice Copper has a lower melting point so it could be obtained in Move for answer Metal Melting Point furnaces at lower temperatures. Furnaces hot enough to extract iron would come later. Cu 1085 C Fe 1585 C
Slide 21 / 186 Slide 22 / 186 Properties of Metallic Compounds REAL WORLD APPLICATION Conductivity Copper is often used in Since the electrons in metals are free to roam somewhat, electrical cable rather than metals are good conductors of electricity! silver even though it is roughly 10% less conductive than silver. Why? Silver is the most conductive metal and is roughly 5-10 times Copper currently trades for roughly 3 dollars an ounce while Move for answer more conductive than steel (mostly iron). silver trades for about 30 dollars a month. It's about the money!!!! Slide 23 / 186 Slide 23 (Answer) / 186 5 Which of the following would NOT conduct electricity 5 Which of the following would NOT conduct electricity in the solid state? in the solid state? A Al A Al B Al 2 O 3 B Al 2 O 3 C NaCl C NaCl Both A and B Both A and B D D Answer Both B and C Both B and C E E E [This object is a pull tab] Slide 24 / 186 Slide 25 / 186 Properties of Covalent Network Substances Properties of Covalent Network Substances Conductivity Melting Point and Boiling Point Since these substances have higher electronegativities, they keep good tabs on their electrons thereby preventing the electrons from Like ionic and metallic substances, covalent network solids are giant moving. As a result they are largely non-conductive. molecules arranged in 3-D crystalline shapes. Here, the atoms involved Diamond and graphite are both allotropes or different versions of tend to semi-metals like Silicon or Germanium or elemental carbon. carbon and vary somewhat in their conductivity. Since the bonds are covalent, they are quite strong! This gives rise to high melting and boiling points! Glass (75% SiO 2 ) Diamond (pure C) Diamond (C) Graphite (C) Melts at 1500 C Melts at 3500 C non-conductive a little conductive
Slide 26 / 186 Slide 27 / 186 REAL WORLD APPLICATION 6 Which of the following would be classified as a covalent network solid? Diamond is notorious for being HARD! This is true for lots of A NaCl covalent network crystals. Can you think of some applications where hardness is important? B HF C CO 2 Ge 2 O 3 D Fe E Body Armor Drill Bits B 4 C (boron carbide) polycrystalline diamond slide for answers Slide 27 (Answer) / 186 Slide 28 / 186 6 Which of the following would be classified as a Molecular Compounds covalent network solid? A NaCl When atoms are bonded covalently, the atoms are held together by sharing electrons. This occurs between non-metals such as B HF C,O,S,H,P,N, etc. Unlike in all of the other substances, the atoms form small individual molecules that then interact with each other and C CO 2 their environment. These are called molecular compounds. D Ge 2 O 3 Fe Answer P O E H H O = C = O D Cl Cl Cl In covalent bonds, electron sharing usually occurs so that atoms attain the electron configurations of noble gases. Both atoms use the shared electrons to reach that goal. Click here to view interactive website [This object is a pull tab] Slide 29 / 186 Slide 30 / 186 Properties of Molecular Substances Properties of Molecular Substances Melting and Boiling Points Conductivity Since these substances contain lots of small molecules, the bonds holding these small molecules together are fundamentally Molecular compounds contain electronegative non-metals and do not different from the covalent bonds found inside the molecule. lose their electrons easily so they are non-conductive. As a result they are excellent INSULATORS! They cover a much larger distance and are quite weak giving rise to LOW melting and boiling points! weak inter-molecular Rubber: (C 5 H 9 ) 250 forces between molecules
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