chapters 1 and 2 - When we are studying organic chemistry...

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When we are studying organic chemistry we are really studying carbon containing molecules What is a molecule? A molecule is comprised of at least 2 atoms strongly (often, covalently) bonded together Examples: H 2 O, O 2 , CO 2 What is an atom? Basic unit of matter that consists of a dense central nucleus and a surrounding electron cloud We can break down a molecule into its atomic components and determine what types of atoms and how many atoms are present in a given molecule through elemental analysis .
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Empirical formulas give the relative ratios of the elements present Compound A has: 78.9% C, 10.6% H Step 1: Assume you have a total of 100 grams of Compound A Step 2: Take the grams of the individual atoms in Compound A and divide that number by the molecular weight of that atom 78.9g C / 12.0g/mole = 6.58 moles C 10.6 g H / 1.01 g/mole = 10.50 moles H 10.5 g O / 16.0 g/mole = 0.66 moles O Step 3: Divide each mole number by the smallest number Here, the smallest number is 0.66 6.58 / 0.66 = 9.97 rounds to 10 10.5 / 0.66 = 15.9 rounds to 16 0.66 / 0.66 = 1 10 16 The results of elemental analysis can be used to give us the empirical formula for a compound. & the rest is O
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Using the empirical formula and the molecular weight of the compound you can get the molecular formula For compound A the molecular weight is 152. What is the molecular Formula? 10 C X 12 gr/mol C = 120 gr 16 H X 1 gr/mol H = 16 gr 1 O X 16 gr/mol O = 16 gr Add to give a total MW = 152 gr So, the empirical and molecular formulas are the same C 10 H 16 O If, the MW of Compound A was 456 gr the molecular formula would be? C H O
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Structure of an atom nucleus Volume around the nucleus where electrons are BUT…Exactly where are the electrons of an atom? - We don’t know exactly where they are but we can determine where electrons are most likely to be This is referred to as the electron density
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Organization of electrons Shell # Max number of electrons orbitals that shell can hold First 2 1 s Second 8 1 s , 2 s , 2 p Third 18 1 s , 2 s , 2 p , 3 s , 3 p , 3 d Fourth 32 1 s , 2 s , 2 p , 3 s , 3 p , 3 d…. Lowest energy highest energy So, we can determine the ground-state electron configuration for various elements Li 1s 2 2s 1 C 1s 2 2s 2 2p 2 Electrons associated with an atom are located in orbitals these orbitals exist in different layers at various distances from the nucleus – these layers are different SHELLS
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1. Pauli Exclusion Principle: each orbital can hold a maximum of 2 electrons Important facts to remember about orbitals: 2. Aufbau principle: fill in the lowest energy orbital first Hund’s Rule: if two or more orbitals of equal energy are vailable for electrons put an electron in its own orbital until each bital has an electron Carbon = Atomic number 6 2p 2s 1s Valence electrons: electrons in the outermost shell ( ) E
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Atomic Orbitals The three 2p orbitals have identical energies. They are degenerate orbitals . s
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This note was uploaded on 02/13/2011 for the course CHEM 2344 taught by Professor Slack,wu during the Spring '11 term at University of Houston.

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chapters 1 and 2 - When we are studying organic chemistry...

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