Transcript Water
The Chemical Basis of Life
BIOLOGY
CHEMICAL COMPOSITION OF LIVING ORGANISMS
All living organisms are made up of matter (anything
that takes up space & has mass)
Matter is composed of elements (the basic
substance or chemical that cannot be broken down)
There are about 25 essential elements necessary for
life; 4 make up 96% of the human body (in this order):
O, C, H, & N
Most of the other 4%: Ca, P, K, S, Na, Cl, & Mg
Trace elements are found in small quantities
http://www.emsb.qc.ca/laurenhill/science/table.jpg
TRACE ELEMENTS & COMPOUNDS
Look at your food labels. Most contain trace
elements (ie. Fe, I, Cr, Co). Water is treated with F
& I.
We need trace elements in our bodies. For
example, Iodine (I) for the thyroid; Iron (Fe) for
blood/O2 transport; Flourine (F) for prevention of
tooth decay
Compounds are substances of 2 or more different
elements; ie. NaCl.
Pure Na 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 within
the nucleus (center) of the atom. The proton # always
remains the same.
2. Neutrons (n) have a neutral or no charge and are also
located within the nucleus of the atom.
3.
Electrons (e-) have a negative charge and orbit the nucleus
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).
An Atom:
http://www.csmate.colostate.edu/cltw/cohortpages/viney/atom.jpg
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)
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.
http://www.findhealer.com/gloss
ary/images/salt.gif
Ionic Bond between Na and Cl, forming NaCl:
http://chem.sci.utsunomiya-u.ac.jp/v9n2/MOzden/image/Figure7.jpg
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
http://upload.wikimedia.org/wikibooks/en/c/c2/Covalent_bo
nd_h.png
http://www.dlt.ncssm.edu/TIGER/Flash/bonding/Coval
entBonding-TN.gif
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-ofwar 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.
Polar Bonds: Water & Chloroform
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http://www.makingthemodernworld.org.uk/learning_modules/c
hemistry/03.TU.02/illustrations/03.IL.14.01.gif
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.
Oxygen
Water Molecules
Hydrogen
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/image12.gif
THE PROPERTIES OF WATER
The properties of water are made
possible b/c of hydrogen bonds.
Cohesion
:
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.
http://www.u413.com/images/Wallpaper/00838_drops_1280x1024.jpg
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).
Adhesion & Capillary Action:
Through
cohesion and
adhesion,
capillary
action occurs.
http://www.waters.com/webassets/cms/category/media/other_images/primer_b_%20thinlayer.jpg
THE PROPERTIES OF WATER, CONT’D
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.
Surface Tension: Jesus Lizard walking on Water:
Can Cohesion, Adhesion, and Surface Tension occur independently?
http://www.societyofrobots.com/images/robot_JB_lizard1.jpg
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).
Frozen Oceans:
http://ngm.nationalgeographic.com/2007/06/vanishing-sea-ice/img/vanishingsea-ice.jpg
http://www.naturetrek.co.uk/pics/t146-large1.jpg
THE PROPERTIES OF WATER, CONT’D
Water is the solvent of life; this means it can dissolve many
substances (due to its polarity).
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+.
Why is this important to life?
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.
ACIDS AND BASES, CONT’D
Human Blood is ~ 7.3-7.4 (a person cannot live
below 7 or above 7.8).
Buffers are substances that stabilize pH.
http://www.epa.gov/acidrain/education/site_students/images/phscale.gif
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
CHEMICAL REACTIONS, CONT’D
__C6H12O6 + __O2 __CO2 + __H2O
C6H12O6 + 6 O2 6 CO2 + 6 H2O
6C
12 H
18 O
6C
12 H
18 O