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Biology 101 Chapter 2 the Chemical Basis of
Life

lOMoARcPSD|122 102 17

Biology 101 Chapter 2 the Chemical Basis of Life
Chemistry = the study of matter and the changes matter
undergoes
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substances whose atoms have the same # of protons
92 elements occur naturally, 25 found in living things
118 known elements
the 4 most important elements (>97% mass)

1) Carbon [C] 2) Oxygen [O] 3) Hydrogen [H] 4)
Nitrogen [N]
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- trace elements
Atom defined: the smallest fundamental particles of
matter that still retain the identity of an element
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Protons

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Neutrons

Charge Mass Location # in atom
Protons Positive 1

Nucleus Constant

Electrons Negative 1/1837 Orbitals Lost or Gained
Neutrons Neutral 1

Nucleus Can alter

Atoms in an uncombined state have the same number of
protons and electrons; therefore they are electrically neutral
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Most of the volume is empty space occupied by orbitals
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The Periodic Table: Atomic Symbols: The Atomic Number:
The Atomic Mass:
Isotopes and mass number

lectron Arrangements Electron shells:
- certain energy levels - 2e - 8e-inoutermost
Valence electrons = bonding electrons and the octet rule

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