Chapter 2 The Chemical Context of Life
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Name ______________________________
Chemical Elements and Compounds
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matter – _____________________________________________________________________________________________
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element – ____________________________________________________________________________________________
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scientists recognize _______ elements in nature
compound – _________________________________________________________________________________________
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examples:
NaCl = _____ Na : _____ Cl
H2O = _____ H : _____ O
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Essential vs. Trace elements
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essential elements – ___________________________________________________________________________________
____________________________________________________________________________________________________
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there are about ______ elements known to be essential to life
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oxygen (O), carbon (C), hydrogen (H), and nitrogen (N), make up ____% of living matter
trace elements – ______________________________________________________________________________________
____________________________________________________________________________________________________
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examples: iron (Fe), iodine (I)
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W/out iodine, goiter (enlarged thyroid gland) can occur. Iodine is an essential ingredient of
a hormone produced by thyroid gland
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Just remember
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Atoms and Molecules
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atom - ______________________________________________________________________________________________
_____________________________________________________________________________________________
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Subatomic Particles
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_______________________ – positively charged and found in the nucleus
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_______________________ – electrically neutral and found in the nucleus
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_______________________ – negatively charged and found around the nucleus
atomic number – _____________________________________________________________
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used to identify an element
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for neutral atoms the atomic number equals the number of electrons
mass number – ______________________________________________________________
____________________________________________________________________________
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also called the atomic mass
isotopes – ___________________________________________________________________
____________________________________________________________________________
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carbon 12 vs. carbon 14
The Energy Levels of Electrons
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energy level – areas of different energies where electrons can be found
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1st energy level – holds ____ electrons
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2nd energy level – holds ____ electrons
Electron Configuration and Chemical Properties
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valence shell – _______________________________________________________________
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valence electrons – ____________________________________________________________
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atoms are unstable and very reactive when they have unpaired electrons in the valence shell
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atoms are stable and very nonreactive (inert) when their valence shells are full
valence number – ____________________________________________________________
____________________________________________________________________________
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the valence number tells you how many bonds an atom can make
Chemical Bonds
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chemical bonds are formed when valence electrons from different atoms interact with each other forming molecules
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electronegativity – ____________________________________________________________________________________
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strongly electronegative atoms attempt to pull the shared electrons toward themselves
Strong Chemical Bonds
1.
covalent bond – ___________________________________________________________________________________
_________________________________________________________________________________________________
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example H-H
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_______________________ covalent bond – bond in which the electrons in a covalent bond are shared equally
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o
bonding atoms are equally electronegative
o
examples: H2, O2, and CH4
_______________________ covalent bond – a bond in which the electrons in a covalent bond are not shared
equally by the two atoms
o
one of the atoms is much more electronegative than the other
o
example: H2O
*Reminder: electronegativity – the attraction of an atom for the electrons of a covalent bond
2.
double covalent bond – ____________________________________________________________________________
________________________________________________________________________________________________
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3.
example: O = O
ionic bond – _____________________________________________________________
________________________________________________________________________
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results from a transfer of electrons between atoms
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ion – an atom (or group of atoms) that has gained or lost an electron
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o
___________________________________ – an ion with a positive electric charge
o
___________________________________ – an ion with a negative electric charge
example: NaCl
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Weak Chemical Bonds
1.
_________________________________________ - in the presence of water ionic bonds are easily disrupted and are
considered weak chemical bonds
2.
_________________________________________ – interaction between a hydrogen atom of one molecule and a very
electronegative atom (oxygen or nitrogen) of another molecule
3.
_________________________________________ – weak attractions between molecules that occur when molecules are
in close proximity and are attracted to each other by charge differences
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4.
occur when electrons are not symmetrically distributed in a molecule
_________________________________________ – weak chemical bond formed when molecules that do not mix with
water congregate to exclude water
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