Water

Report
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
http://cache.eb.com/eb/image?id=96904&rendTypeId=4
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

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