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Biology
The Chemical Basis of Life
CHEMICAL COMPOSITION OF LIVING ORGANISMS
 ALL LIVING ORGANISMS ARE MADE UP OF ________________(ANYTHING THAT TAKES UP
SPACE & HAS MASS)
 _________________________________
IS COMPOSED OF ELEMENTS (THE BASIC
SUBSTANCE OR CHEMICAL THAT CANNOT BE BROKEN DOWN)
 THERE ARE ABOUT ________________________________________ NECESSARY FOR LIFE;
4 MAKE UP 96% OF THE HUMAN BODY (IN THIS ORDER): ___________________________
 MOST OF THE OTHER 4%: _____________________________________________________
 __________________________________________ ARE FOUND IN SMALL QUANTITIES
TRACE ELEMENTS & COMPOUNDS
 Look at your food labels. Most contain trace elements (ie.________________________).
Water is treated with _____________________.
 We need trace elements in our bodies. For example, Iodine (I) for the_________________;
________________ (Fe) for blood/O2 transport; Flourine (F) for prevention of tooth decay
 ______________________________ are substances of 2 or more different elements; ie. NaCl.
 Pure Na (sodium) is an explosive metal; pure Cl (chlorine) is a poisonous gas, but when
together they form an edible solid compound!
Atoms have Particles
Atoms, meaning indivisible, are the smallest units of matter, contain particles:
1. Protons (p+) have a positive charge and are located in the ____________(center) of the atom.
The proton # always _________________________________________________________
2. Neutrons (n) have a neutral or no charge and are located in the ______________ of the atom.
3. Electrons (e-) have a negative charge and ________________________of the atom in a cloud.
 They move in 3D, not just in a circle. They are separated by levels and the further
away from the nucleus, the greater the energy they have.
 These take place in chemical reactions (rxns).
Atoms have Particles, Cont’d
 Elements have a unique # of p+; this is the atomic number. Ex.) Helium (He) has the atomic
# of 2 and has 2 p+; C has 6 p+ and the atomic # of 6.
 Generally, the proton # = the electron #
 Atomic mass is the p+ + the n or the sum of the nucleus. Ex.) He = 4; C = 12 (b/c the mass
of the p+ = the mass of n)
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 When some atoms of the same element have different mass numbers, their n # is different.
These are isotopes. The p+ and e- are the same! Ex.) C-12, C-13, and C-14 (written 12C, 13C,
and 14C).
 14C is a radioactive isotope; this means the nucleus spontaneously decays (emitting
radioactivity). This is used to date fossils.
Ionic Bonds
 Na has 1 e- in its outermost shell; Cl has 7 e- in its outermost shell. Cl is anxious to
gain 1 e- to fill the octet rule while Na is more than willing to give up that 1 e- to
satisfy that rule.
 Ionic bonds form as the result of e- transfer; 1 element gives/donates an e- while
the other element receives/accepts the e-. In this case, Na donates, Cl receives.
 These bonds result in atoms (or molecules) w/ electrical charges and are a.k.a.
ions.
 The compounds that formed are salts which exist as crystals in nature and readily
dissolve in water.
Covalent Bonds
 Covalent Bonds are strong bonds that share e-; these form molecules.
 These can be single (1 e- pair shared), double (2 e- pairs are shared, or 2 e-) or
triple (3 e- pairs are shared, or 6 e-).
 Some covalent bonds share e- equally; this is a nonpolar covalent bond. Ex.) H2, O2,
CH4
Covalent Bonds, Cont’d
 However, most covalent bonds do not share e- equally. These are polar covalent
bonds. Ex.) H2O.
 Polar covalent bonds will result in a molecule that has atoms in a tug-of-war for
the e-; the more electronegative an atom is, the closer the e- will be to that atom.
 Electronegativity is an atom’s pull, or attraction, for shared e- (that is, those e- in a
covalent bond).
 Note: for the scope of this course, O is the most electronegative atom (N & F are
also electronegative)
 Let’s look at H2O: O will pull the e- a little closer to itself, leaving the H’s slightly
positive (the O will be slightly negative as a result). This means the e- will hang
out more often with the O than the H’s.
 B/C this molecule forms a polar covalent bond & each atom has a slight charge,
this is a polar molecule. There is an unequal distribution of charges.
Hydrogen Bonds
 Hydrogen bonds are weak bonds that are crucial to the 3D shape of large
molecules (DNA & proteins).
 Can be found in molecules that have polar covalent bonds. Ex.) H2O + H2O
 Are the reason for the properties of H2O.
 Form between a H of 1 molecule AND a N OR O of another molecule.
 They form and break quickly.
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 The Properties of WaterThe properties of water are made possible b/c of hydrogen
bonds.
 Water is a requirement of life & the properties of water make it essential to live.
The properties of water include:
 Cohesion, Adhesion, Surface Tension, Temperature Moderation, Existing in 3 States
Naturally, & Solvent of Life
 Cohesion is the ability/tendency of molecules (in this case H2O molecules) to stick
together (to other H2O molecules).
 IF water evaporates (from the leaves), water will travel up from the roots to
the leaves b/c of cohesion (water sticks to water). This will also carry
dissolved nutrients that the plant needs for survival.
 Adhesion is the ability of one molecule to stick to something else; in this case H2O
can stick to the veins or cell walls of the plant.
 This is how capillary action occurs (water travels against gravity or up the plant
thru the veins b/c water sticks to the sides of the plant’s walls).
Through cohesion and adhesion, capillary action occurs
 Adhesion is the ability of one molecule to stick to something else; in this case H2O
can stick to the veins or cell walls of the plant.
 This is how capillary action occurs (water travels against gravity or up the plant
thru the veins b/c water sticks to the sides of the plant’s walls).
 Surface Tension is the difficulty of H2O to stretch or break; H2O has a high surface
tension (difficult to break).
 Water’s moderate temperature is due to the H Bonds. H2O can resist temp changes;
this keeps the Earth’s temp within limits (to sustain life).
 Due to the large volume of H2O on Earth’s surface, climate is regulated.
Water stores heat (from the sun) during warm times and releases heat
during cold times.
 Heat is the amount of energy to move atoms and molecules.
 Temperature is the measurement of heat (average speed of atoms and
molecules, not the total amount of heat).
 Evaporative cooling is the process of heat escaping from the body in the form
of sweat. As sweat evaporates from the skin, cooling results.
The Properties of Water, Cont’d
 Water exists naturally in 3 states: as a solid, liquid and a gas (water vapor).
 When water freezes, it is less dense than when it is in liquid form. Why? H Bonds!
 The H Bonds stabilize & hold a crystalline pattern (at arms length). This allows ice
to float on water (in the liquid state).
 This is an important property b/c only the top layer of water (in a body of water)
will freeze & it will not sink.
 This allows life in the water environment to survive. Also, the ice insulates the
water (like a blanket from the cold air).
 Water is the solvent of life; this means it can dissolve many substances (due to its
polarity).
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 When water is a solvent (agent that dissolves) & forms a solution (a liquid with 2
or more substances mixed together), water is an aqueous solution.
 The solute is the dissolved substance (salt, sugar, etc).
 This property is important to life b/c many substances (polar and/or ionic) must be
transported in the body (an organism). Ex.) Blood’s main component is H2O and is
contains dissolved ions, salts, gases, wastes, sugars, and proteins for transport.
Acids and Bases
 The hydrogen ion is the H+ and cannot exist alone.
 The hydroxide ion is the OH- and can exist alone.
 The hydronium ion is the H3O+.
 Ions regulate pH.
 The pH Scale is a range of numbers that indicate the amount or concentration of H+
or OH- in a solution. It ranges from 0-14.
 A neutral solution is a solution that has an equal concentration of both ions. The
pH is 7 (mid-range). Pure water is neutral.
 An acidic solution is a solution that has an increased concentration of H+. It has a
low pH (below 7). More H+, less OH-, low pH.
 A basic solution is a solution that has an increased concentration of OH-. It has a
high pH (greater than 7). Less H+, more OH-, high pH.
 Human Blood is ~ 7.3-7.4 (a person cannot live below 7 or above 7.8).
 Buffers are substances that stabilize pH.
Chemical Reactions
Chemical Reactions- making and breaking bonds.
__H2 + __ O2  __H2O
 Reactants (starting materials)  Products (results)
 Always balance equation! This means the # of atoms (H, O, etc) on the left side of
the equation MUST equal the # of atoms (H, O, etc) on the right side of the
equation.
Try this:
 __C6H12O6 + __O2  __CO2 + __H2O