Chem 1100 Lecture 5 Outline of Last Lecture I. IsotopesII. How Particles ReactIII. Molecules & ModelsIV. Octet RuleV. Waves of LightVI. Frequency & WavelengthOutline of Current Lecture I. RECAP Converting Wavelength and FrequencyII. Lewis StructuresIII. Resonance StructuresCurrent LectureI. Converting Wavelength and Frequencya. What is the frequency of light if its wavelength is 200 m?i. Λ = C/V ---- V = C/ λii. 3.00 x 10^8 m/s = 1,500,000 s^-1 or 1.5 x 10^ s^-1b. Radiation from the sunThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. 200 Mc.II. Lewis Structuresa. As you move from left to right across the periodic table each element has one more electron in its outer shell than the one before it. Hydrogen has 1. Helium has 2. On the next level. Li has one. Be has two. B has three. C has four. N has five. O has six. F has seven. And Ne has 8. Eight electrons is a full shell. b. If you combine carbon with 4 hydrogen atoms you can create methane. Nitrogen can combine with three hydrogens and make ammonia. Oxygen can combine with two hydrogens and make water. c. This is an example of the Lewis structure for ammonia. d. Hydrogen is the simplest molecule/atom there is.e. Covalent “shared strength” bonds – when two atoms share electrons to help each other become more stable and fill their outer shells.f. The first shell only has room for two electrons since its so close to the nuclei and so small.g. EXAMPLES of Lewis Structures:i. H2 H – Hii. Cl2iii. H2O h. Carbon tends to form 4 bonds, nitrogen tends to form 3 bonds, oxygen tends to form 2 bonds, and Hydrogen and Fluorine tend to form one bond.i. How to draw Lewis Structures: The Processi. Find the number of valence electrons 1. C02 2. How many valence electrons are in this molecule?3. How many valence electrons are in carbon? 4. It’s in group 4A.4. How many valence electrons does oxygen have? 6. It’s in group 6A.5. There are two oxygen atoms. So you have 12 from oxygen and 4 from carbon. That’s 16. ii. Write the skeletal structure.1. The atom that’s lowest in frequency will be in the middle. 2. CO2 has two single bonds.3. Skeletal structure: O – C - Oiii. Put electron pairs around the “outside” of atoms until they have an octet.1.iv. Put any remaining electrons in pairs on the central atom. 1. None in this case.v. Formal Charge:1. Formula: Take the group number and then subtract the number ofbonds “dashes” and then subtract the number of non-bonding electrons “dots”.vi. If needed, use long pairs from “outside” atoms to make multiple bonds, giving the central atom an octet.1. Example: 2. Both of the structures above are the same. The top one has double bonds and the bottom one has single bonds. 3. FYI: when drawing skeletal structures do not draw ozone as a triangle.IV. Resonance Structuresa. When more than one Lewis structure can be drawn, the molecule or ion is said tohave resonance. The individual Lewis structures are termed contributing resonance structures.b. Why the reactivity difference? i. A double bond is stronger because it is harder to break.ii. The weaker the bond the more reactive the
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