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Essential Chemistry for Biology
Chapter 2
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Tracing Life Down to the Chemical Level
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Basic Chemistry
Matter Anything that takes up
space and has mass Can exist as a liquid,
solid, or gas Elements
Basic building block of matter
92 naturally occurring elements
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Basic Chemistry
Only 6 elements that make up most of the body weight of organisms C CarbonH HydrogenN NitrogenO OxygenP PhosphorusS Sulfur
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Trace Elements
Trace elements make up 0.01% of human body weight, but still very important
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Each Element Consists of ONE Kind of Atom
Smallest unit that retains the properties of a given element And to enter a chemical reaction
Composed of subatomic particles: Protons (p+) Neutrons Electrons (e-)
Move @ atomic nucleus Usually (e-) = (p+)
Electrically neutral
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Atomic Symbol
Atomic Mass = Number of Protons + Number of Neutrons
Atomic Number = The Number of Protons in the Nucleus
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Valence Shell
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Molecules and Compounds
Molecules Chemical bonding that joins atoms Some contain atoms of only one element
N2
Compounds Atoms of two or more different elements
H2O Mixture
Two or more molecules mingling together
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Chemical Bonds
Atoms are held together by bonds 3 main types:
Ionic bond Accept or donate electrons
Covalent bond Share one or more electrons
Hydrogen bond
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Ionic Bond
Atoms gain and lose electrons Balance between protons
and electrons shifts Become “ionized”
Ion Atom that has a charge Losing an electron results
in a net positive Gaining an electron results
in a net negative charge Ionic bond
Association of two ions that have opposing charges
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Which will form an ionic bond?
Potassium (K)
Chlorine (Cl)
Helium (He)
Argon (Ar)
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Can Mg and Cl form an ionic bond?
Magnesium (Mg)Chlorine (Cl)
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Covalent Bond
Covalent bond Stable and stronger
than ionic bonds Atoms share
electrons Each atom will
have a completed outer shell
Bond Notation Single covalent
bonds are written as H-H
Double covalent bonds are written as O=O
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A covalent bond can be nonpolar or polar
Nonpolar covalent bond Sharing of electrons
between atoms is fairly equal
Polar covalent bond Unequal sharing of
electrons
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Hydrogen Bond
Hydrogen bond Weak attraction
Form and break easily
Occurs between polar molecules
Polar bonds have charges on either end and often attract to each other
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Chemical Reactions
Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones
Reactants Starting materials
Products End materials
Chemical reactions cannot create or destroy matter, They only rearrange it
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Solvent of life
Water dissolves other polar substances
Solvent Ions and polar molecules
easily dissolve in it Solute
A dissolved substance Hydrophilic
water-loving molecules form hydrogen bonds with
water Hydrophobic
water-fearing molecules do not form hydrogen
bonds with water
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Acids and Bases
When water ionizes, it releases an equal number of hydrogen ions (H+) and hydroxide ions (OH-)
Some substances release more or fewer or each Acids - Excess hydrogen ions Bases - Excess hydroxide ions
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Acidic and Basic Solutions
Acidic Solutions Sharp, sour taste Molecules that
dissociate in water Release
hydrogen ions (H+)
Basic Solutions Bitter taste Molecules that
either take up hydrogen ions (H+) or release hydroxide ions (OH-)
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pH Scale
The pH Scale Ranges from 0 - 14
pH below 7 is acidic [H+] > [OH-]pH above 7 is alkaline [OH-] > [H+]pH of 7 is neutral [H+] = [OH-]
Buffer Chemical or combination of chemicals that
keeps pH within normal limits
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