Chapter 2. The Chemical Context of Life - Explore Biology ... · AP Biology 2005-2006 Everything is...
Transcript of Chapter 2. The Chemical Context of Life - Explore Biology ... · AP Biology 2005-2006 Everything is...
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2005-2006AP Biology
Chapter 2.
The Chemical Context of Life
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2005-2006AP Biology
Why are we studying chemistry?
Biology has chemistry at its foundation
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2005-2006AP Biology
Everything is made of matter Matter is made of atoms Atoms are made of:
protons + mass of 1 nucleus neutrons 0 mass of 1 nucleus electrons - mass <<1 orbits
Different kinds of atoms = elements
The Basics
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2005-2006AP Biology
The World of Elements
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2005-2006AP Biology
Models of atoms
(c)
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2005-2006AP Biology
Atomic structure determines behavior The number of protons in an atom
determines the element # of protons = atomic number this also tells you # of electrons
All atoms of an element have samechemical properties all behave the same properties don’t change
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2005-2006AP Biology
Life requires ~25 chemical elements About 25 elements are essential for life
Four elements make up 96% of livingmatter:
• carbon (C) • hydrogen (H)• oxygen (O) • nitrogen (N)
Four elements make up most ofremaining 4%:
• phosphorus (P) • calcium (Ca)• sulfur (S) • potassium (K)
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2005-2006AP Biology
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2005-2006AP Biology
Isotopes Different number of neutrons (heavier) Some are unstable
nuclear reactions / decay Split off neutrons &/or protons
radioactivity Biological tool Biological hazard
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2005-2006AP Biology
Bonding properties Effect of electrons
chemical behavior ofan atom depends on itselectron arrangement
depends on thenumber of electrons inits outermost shell, thevalence shell
How does this atom behave?
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2005-2006AP Biology
Bonding properties Effect of electrons
chemical behavior of an atom depends onnumber of electrons in its outermost shell
How does this atom behave? How does this atom behave?
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2005-2006AP Biology
Elements & their valence shells Elements in the same row have
the same number of shells
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2005-2006AP Biology
Elements & their valence shells Elements in the same column
have the same valence & similarchemical properties
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2005-2006AP Biology
Elements & their valence shells Moving from left to right, each
element has a sequential additionof electrons (and protons)
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2005-2006AP Biology
Chemical reactivity Atoms tend to
Complete a partially filled outer(valence) electron shell
or Empty a partially filled outer (valence)
electron shell
This tendency drives chemical reactions
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2005-2006AP Biology
Ionic bonds
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2005-2006AP Biology
Ionic bonds Transfer of an electron Forms + & - ions
+ = cation – = anion
Weak bond example:
salt = dissolveseasily in water
“Let’s go to the video tape!”(play movie here)
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2005-2006AP Biology
Covalent bonds Two atoms need an electron Share a pair of electrons Strong bond
both atoms holding onto the electrons Forms molecules
example: water = takes energy to separate
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2005-2006AP Biology
Double covalent bonds Two atoms can share more than one
pair of electrons double bonds (2 pairs of electrons) triple bonds (3 pairs of electrons)
Very strong bonds
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2005-2006AP Biology
Multiple covalent bonds 1 atom can form covalent bonds with
two or more other atoms forms larger molecules ex. carbon
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2005-2006AP Biology
Polar covalent bonds Pair of electrons not shared equally by
2 atoms Water = O + H
oxygen has stronger“attraction” for theshared electrons thanhydrogen
oxygen has higherelectronegativity
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2005-2006AP Biology
Polar covalent bonds 2 hydrogens in the water molecule
form an angle Water molecule is polar
oxygen end is – hydrogen end is +
Leads to manyinteresting propertiesof water….
“Let’s go to the video tape!”(play movie here)
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2005-2006AP Biology
Hydrogen bonds Positive H atom in
1 water molecule isattracted to negative Oin another
Can occur wherever an-OH exists in a largermolecule
Weak bonds
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2005-2006AP Biology
Reductionist view of biology Matter is made of atoms Life requires ~25 chemical elements Atomic structure determines behavior of an
element Atoms combine by chemical bonding to form
molecules Weak chemical bonds play important roles in
chemistry of life A molecule’s biological function is related to its
shape Chemical reactions make & break chemical bonds