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Lecture 6

BIOL 1201 Lecture Notes - Lecture 6: Chemical Polarity, Molecular Mass, Chemical Formula


Department
Biological Sciences
Course Code
BIOL 1201
Professor
Bill Wischusen
Lecture
6

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Week 2: August 29- September 2
Pre reading for next class: pages 58-77
I. Strong Bonds- when we’re talking about the structure of a molecule, these are the bonds
we are talking about. The bond inside of a molecule is polarity
a. Ionic- tends to be polar. Oppositely charged ions are attracted to each other which
is described as Ionic polarity
b. Covalent
c. Polar covalent
II. How do bonds influence the polarity of a molecule
a. Molecules which contain ionic bonds will be polar
b. Molecules which contain polar covalent bonds will be polar, (just with a few
exceptions)
c. Molecules which contain covalent bonds will be non- polar; shared equally
(nonpolar); will not go into a solution in water
III. What determines the number and type of chemical bonds?
a. Number of bonds is determined by the valence; number of electrons in the
outermost shell
b. The type of bond is determined by the electronegativity- how much the atoms want
the electrons
IV. Electronegativity
a. Electronegativity is a measure of the tendency of an atom to attract a bonding pair
of electrons
b. Measure of the attraction an atom has for electrons.
c. The one exception is hydrogen and carbon because they turn out to have almost the
same electronegativity; the bond between them turns out to be a nonpolar covalent
bond. The two elements are the same, so they normally would be covalent, but this
is the exception.
V. Weak bonds
a. Bonds which are not involved in making a substance.
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b. Not because they are involved in making a substance, not want holds substances
together; they are important in determining shape and different properties.
c. Weak attraction between atoms on different molecules or different parts of a large
molecule
d. Occur between molecules that have polar covalent to ionic bonds
e. Always involves a Hydrogen; attraction between molecules. When you have a bunch
of water molecules, they are all attached to each other by weak bonds. It’s a polar
molecule. The hydrogen end of one end of the molecule is attracted to the oxygen
end of another.
VI. Molecules and compounds
a. Compound
a.i. A substance consisting of two or more different atoms, in specific
proportions, bonding together in a specific pattern
b. Molecule
b.i. The smallest unit of a compound that retains all of the properties of that
compound
VII. Molecular Formulas
a. Water= H2O
a.i. There is only one way to put two hydrogens and one oxygen together (can
only make water)
b. Carbon dioxide= CO2
c. Glucose= C6H12O6
c.i. Different ways to arrange this together
VIII. Isomers
a. Molecules with the same molecular formula, but a different arrangement of atoms
b. As molecules get more complex, there are more isomers
c. Mirror images, they are exactly the same but are not. You can’t get the two in the
right orientation. In many cases, one form will be active and another will be
inactive.
IX. Molecular weight
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a. The sum of the atomic masses for all of the atoms in a molecule
b. Examples:
b.i. H2O= (1x2) + 16= 18 daltons
b.ii. CO2= (16x2) + 12= 44
b.iii. C12H22O11= (12x12)(1x22)(16x11)= 144+22+176= 342
b.iv. C254H377N65O75S6
X. Gram Molecular Weight
a. The mass of a substance equal to its molecular weight in grams
b. Contains a constant number of molecules
c. It there is a mass equal to the molecular weight in grams
d. If we have the mass, we can determine how many molecules
e. Avogadro’s Gram Molecular Weight
e.i. 18 grams of water has the same number of molecules as?
e.i.1. 44 Grams of CO2
e.i.2. 342 Gams of Sucrose
XI. Moles and Molar Concentration
a. 1 mole= the mass of a substance equal to its gram molecular weight
b. 1 molar solution= a solution containing 1 mole of a substance per 1 liter of solution
Day 2
XII. Properties of Water
a. Cohesive and adhesive
a.i. Cohere means to stick together. They stick together because of their
hydrogen bonds- polar.
a.ii. Water molecules cling to glass in a tube and pull themselves up into it
b. High specific heat
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