Covalent Bonding Note: Students and classrooms with iPads should - PDF document

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 Table of Contents: Covalent Bonding Click on the topic to go to that section · Covalent versus Ionic Bonds · Properties of Ionic and Covalent Materials · Naming Binary Molecular Compounds · Lewis Structures · Resonance Structures · VSEPR Theory · Molecular Geometry · Polarity

Slide 4 / 186 Covalent versus Ionic Bonds Return to Table of Contents Slide 5 / 186 Covalent Bonding & Molecular Geometry Examine these two forms of the same compound, ibuprofen. Slide 6 / 186 Covalent Bonding & Molecular Geometry This form of ibuprofen is about This form of 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 Covalent Bonding & Molecular Geometry Take a look around you. The chemistry of everything you see, hear, feel, touch and taste is a result of not only what it's made of but also how it's put together. (Remember this for next year in biology!) In this unit, we will explore what causes molecules to have various shapes. Later, we will then examine how molecular geometry affects different chemical properties. Slide 8 / 186 Chemical Bonds Chemical bonds hold atoms together to create chemical compounds. There are three basic types of bonds: Ionic - The electrostatic attraction between ions Covalent - The sharing of electrons between atoms Metallic - Each metal atom bonds to other metals atoms within a "sea" of electrons (covered in a later unit) Slide 9 / 186 Chemical Bonds How ionic or covalent a bond is depends on the difference in electronegativity. The smaller the difference, the more likely electrons are "shared" and the bond is considered covalent, the greater the difference, the more likely electrons have been transferred and the atoms are ionized resulting in an ionic bond. Li Be B C N O F Electronegativity 1.0 1.6 2.0 2.5 3.0 3.5 4.0 Bond Li-F Be-F B-F C-F N-F O-O F-F Electronegativity 3 2.4 2.0 1.5 1 0.5 0 Increasing Covalent Character

Slide 10 / 186 Chemical Bonds We can make a few simplifications... Ionic Bonding Ionic bonds occur when the difference in electronegativity between two atoms is more than 1.7. Na ---- F electronegativity = 3 Covalent Bonding If the difference of electronegativity is less than 1.7, neither atom takes electrons from the other; they share electrons. This type of bonding typically takes place between two non-metals or between two metals. H ---- Cl electronegativity = 1.1 Slide 11 / 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! Slide 12 / 186

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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 Properties of Ionic Compounds Boiling and Melting Points Since the attractions between the ions span a short distance, these forces are quite strong resulting in high melting points and boiling points! Na+ -- Cl- it takes a lot of energy to break an ionic lattice! Compound Melting Point (C) NaCl 801 MgO 2852

Slide 18 / 186 Properties of Ionic Compounds Conductivity Since ionic compounds consist of ions, when these ions are free to move, the substance can conduct electricity. To move, they must be in the liquid or molten state. + + - - - + - + + - NaCl (s) Molten NaCl(l) Lattice is strong, no conductivity Lattice is broken, ions are free to move and conduct Slide 19 / 186 Properties of Metallic Substances Melting and Boiling Points 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 gives rise to high melting and boiling points! strong metallic covalent bonds Metallic Lattice Metal Melting Point Cu 1085 C Fe 1585 C Slide 20 / 186 REAL WORLD APPLICATION In order to obtain pure metals, the ancients had to melt the metal (metallic substance) out of the rock (an ionic compound). Why do you think the bronze age (copper mixed with tin) came before the iron age? Copper has a lower melting point so it could be obtained in Move for answer furnaces at lower temperatures. Furnaces hot enough to extract iron would come later.

Slide 21 / 186 Properties of Metallic Compounds Conductivity Since the electrons in metals are free to roam somewhat, metals are good conductors of electricity! Silver is the most conductive metal and is roughly 5-10 times more conductive than steel (mostly iron). Slide 22 / 186 REAL WORLD APPLICATION Copper is often used in electrical cable rather than silver even though it is roughly 10% less conductive than silver. Why? Copper currently trades for roughly 3 dollars an ounce while Move for answer silver trades for about 30 dollars a month. It's about the money!!!! Slide 23 / 186 5 Which of the following would NOT conduct electricity in the solid state? A Al B Al 2 O 3 C NaCl D Both A and B Both B and C E

Slide 23 (Answer) / 186 5 Which of the following would NOT conduct electricity in the solid state? A Al B Al 2 O 3 C NaCl Both A and B D Answer Both B and C E E [This object is a pull tab] Slide 24 / 186 Properties of Covalent Network Substances Melting Point and Boiling Point Like ionic and metallic substances, covalent network solids are giant molecules arranged in 3-D crystalline shapes. Here, the atoms involved tend to semi-metals like Silicon or Germanium or elemental carbon. 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) Melts at 1500 C Melts at 3500 C Slide 25 / 186 Properties of Covalent Network Substances Conductivity Since these substances have higher electronegativities, they keep good tabs on their electrons thereby preventing the electrons from moving. As a result they are largely non-conductive. Diamond and graphite are both allotropes or different versions of carbon and vary somewhat in their conductivity. Diamond (C) Graphite (C) non-conductive a little conductive

Slide 26 / 186 REAL WORLD APPLICATION Diamond is notorious for being HARD! This is true for lots of covalent network crystals. Can you think of some applications where hardness is important? Body Armor Drill Bits B 4 C (boron carbide) polycrystalline diamond slide for answers Slide 27 / 186 6 Which of the following would be classified as a covalent network solid? A NaCl B HF C CO 2 Ge 2 O 3 D Fe E Slide 27 (Answer) / 186 6 Which of the following would be classified as a covalent network solid? A NaCl B HF C CO 2 Ge 2 O 3 D Fe Answer E D [This object is a pull tab]

Slide 28 / 186 Molecular Compounds When atoms are bonded covalently, the atoms are held together by sharing electrons. This occurs between non-metals such as 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 their environment. These are called molecular compounds. P O H H O = C = O 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 Slide 29 / 186 Properties of Molecular Substances Melting and Boiling Points Since these substances contain lots of small molecules, the bonds holding these small molecules together are fundamentally different from the covalent bonds found inside the molecule. They cover a much larger distance and are quite weak giving rise to LOW melting and boiling points! weak inter-molecular forces between molecules Slide 30 / 186 Properties of Molecular Substances Conductivity Molecular compounds contain electronegative non-metals and do not lose their electrons easily so they are non-conductive. As a result they are excellent INSULATORS! Rubber: (C 5 H 9 ) 250