Chemistry

موضوع: Chemistry الجمعة ديسمبر 12, 2008 4:08 pm

A knowledge of basic chemistry is important for understanding just about any
area of biology from the function of cells to the behavior of organisms and the
ecological relationships between organisms and their environment.
Indeed, chemists are fond of teasing biologists by claiming that all biology
is chemistry*. While this isn't quite true, in order to make sense of the
structure of cells and organisms a little chemistry goes a long way.

"Ball and Stick" Model of a Heme group. This group is part of a larger
molecule, hemoglobin. Grey=Carbon, Blue= Nitrogen, Red= Oxygen. Hydrogens not
shown.
*Of course the physicists say that all chemistry is physics!
Created 8/22/96;Revised 01/04/00 PGD

Atoms and
Elements.

VBS Home page,VBS Course Navigator, Basic chemistry,
Introduction, Previous Page, Next Page,top of page

Atoms are basic components of
the matter we are familiar with. Atoms are the smallest part of matter that have
chemical properties characteristic of a particular chemical element. Most of the
mass of an atom is due to the atomic nucleus. The nucleus consists of protons
which have a positve electrical charge and neutrons which have no charge. This is a representation of a carbon atom. Previous Page
Atomic number and atomic
mass. The atomic number of an atom is the number of protons in the atom
which, if the atom is neutral, equals the number of electrons. This is important
because the number of electrons is related to the chemical properties of the
atom. The atomic mass is the total mass of the electrons, protons, neutrons in
the atom. Previous
Page
Isotopes are atoms that have
the same atomic number(number of protons) but differ in atomic mass. For
instance most carbon has six protons and six neutrons and thus atomic mass of of
approxiately 12. Some carbon atoms have an atomic mass of 13 so thus have six
protons and seven neutrons. All isotopes of the same element have about the same
chemical properites because the number pattern of electrons is the same.
Previous
Page
Radio-isotopes. Many
elements have multiple isotopes, some of which may ne radioactive. Radioactive
isotopes are called radio-isotopes and are characterised by a constant rate of
decay into other elements or isotpes. Some common isotopes in biology and their
half lives are here. Previous Page
The half life of a
radio-isotope is the time in which it takes half of a starting amount of
radio-isotope to decay into something else. This decay is accompanied by the
release of various forms of radiation. This is important for biologists because
it allows biologists to use radioisotopes to trace the fate of elements in
biological systems and to date fossils by measuring the ratios of different
radio-isotopes in the fossil. Previous Page
Electrons are small
components which are surrounding the nucleus. Electron have a negative charge.
An atom with no net electrical charge has the same number of electrons as
protons. Electrons are restricted to certain energy levels "shells" and orbitals
within those energy levels and these energy levels and orbitals fill in a
regular pattern from the lowest energy level outward. Here is an illustration of the orbitals of a carbon
atom's outer energy level. Orbital is in some sense a bad word because electrons
tend to behave rather strangely in that its orbit is best described as a
probability density. Previous Page
Electrons are important for several reasons:

Chemical bonds are formed when electrons are
transfered or shared between atoms.
The arrangement of electrons in the atoms of an element help to determine
the chemical properties of an element. For example
when the outer most energy level of an atom is almost empty, the atoms of the
element tend to give up electrons. A good example is sodium. When the outermost
energy level of an atom is almost (but not completely) full, the atoms of the
the element tend to grab electrons from other atoms. A good example is chlorine.
Finally electrons can carry and store energy and this is important in
understanding metabolism. Everytime a chemical reaction takes place, elecrons
are shared or transferred between atoms and hence energy is shared or
transferred. For example, in photosynthesis light energy is captured and stored
by electrons. Then the electrons are used to make glucose, and other organic
molecules which store the energy as potential energy in their chemical bonds.

» http://chemistry.about.com/od/sciencefairproject1/a/caffeinetyping.htm