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Unformatted text preview: Chapter 19
Atoms, Molecules, and ExtendedBonding Substances (oh, my!)
Did you read all of Chapter 19 for today?
No Chemical matter is classified into a number
of types Elements vs Compounds Elements: only one kind of atom Compounds: two or more kinds of atoms Which are elements? Which are compounds? Chemical Bonds The constituent atoms in molecules are held together by “bonds”. A bond is usually a pair of electrons.
• Strong Bonds: Metallic, Ionic, Covalent
• Weak Bonds: van der Waals, Hydrogen Quantum Model Explains Them All!
• Chapters 2023 will feature each of the bonding types In our visual models we often use sticks to represent bonds, and balls to represent atoms How does bonding work? Atoms give up, obtain, or share electrons and in the process combine to form the substances around us. Bonding involves only the electrons in the outermost, unfilled orbitals: the valence electrons. All other inner electrons don’t matter as far as bonding is concerned! All bonding involves atoms sharing or exchanging electrons in a “stable” way. Stability means:
• To fall to a lower energy state and thus be more tightly bound.
• To completely fill an orbital set. Writing chemical formulas for molecular
matter Identify atoms in a molecule Give the number of each atom type Examples
• CH4 Write down the chemical formula for these
two molecules Hydrogen peroxide Bleach and disinfectant Glycine One of the 23 essential
Amino acids Chemical Formulas for Network/Extended
metallic 1. Identify kinds of atoms
2. Give the relative number of each atom type
SiO2 Molecules have shapes How many ways can you arrange Carbon and Hydrogen? Guess the shape of Benzene • C6H6 Planar Tetrahedral
Linear Friedrich August Kekulé
discovered benzene’s structure
discovered The shape of a molecule is determined by
molecular orbitals When H2 was formed from H, energy was released as heat. So in H2 each electron needs more energy than before to escape. H has a different discrete spectrum than H2. This allows astronomers to tell the temperature of hydrogen gas. H H H2 The electrons sit lower in the energy well than before Molecules belong to families -Hydrocarbons
are present? Methane -- CH4
Propane -- CH3CH2CH3
All react to form CO2 and H2O Octane -- CH3CH2CH2CH2CH2CH2CH2CH3
methane, propane, octane belong to hydrocarbon family
all three are used as fuels What formula represents this family of
D. C2nHn CH4 C3H8 where n is an integer starting with 1 C4H10 Another molecular family – Organic acids
CH3CO2H -- Acetic acid (gives vinegar its taste)
What groups of atoms are common to all three molecules?
Lauric acid – in coconut milk CH3__
__ CO2H (carboxyl) CH3(CH2)14CO2H -- Palmitic acid (palm oils, and animals)
family of organic acids all three are in foods we eat Amino Acids, the building blocks for
NH2CH2CO2H NH2CHCH3CO2H NH2C10H9NHCO2H What elements
are present? Formulas?
What groups of atoms
are common to all
(amine) family of amino acids –
acid group + amino group -- also in foods we eat __ CO2H (Carboxyl)
CO (Carboxyl) Deducing molecular formulae and structures:
Time-of-Flight Mass Spectrometer
Number of fragments accelerator plates positive fragments Length of flight path
kinetic energy = ½(mass)(speed)2 If all fragments are given the same kinetic energy, which ones get to the detector first? time Deducing molecular structure with a mass
spectrometer Deducing molecular structure with a mass
Masses of molecular
fragments Mass Spectroscopy
Mass Spectroscopy C9O4H8
Mass of the molecule
180 amu Motion within a molecules Bonds are not rigid • lengths change
• Bond angles bend – angle opens and closes The various types of stretches and bends occur with different energies Energy depends on how stiff the bond is and the atomic masses that are moving. A simplified view of infrared spectroscopy
(continuous with dark bands) continuous
IR spectrum Detector Infrared Source Analogous visible continuous spectrum Sample Analogous visible absorption spectrum IR spectroscopy can be used to deduce
chemical formulas and structures
IR Vibrational Spectroscopy
fingerprint region C9O4H8
C=O Energy of vibration Different molecular groups vibrate in different regions A portion of the IR spectrum for each molecule is shown.
Formulate a hypothesis about what portion of the molecule
gives rise to the sharp set of peaks labeled P?
B. OH group
Hydrocarbon part P P PA P
A How do we deduce chemical formulas and
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This note was uploaded on 11/30/2011 for the course PHY S 100 taught by Professor Staff during the Winter '08 term at BYU.
- Winter '08