Weed Science, PLS 4601c Section 7644
and Grad. – Prin. Of Weed Science AGR 6932 Section 9212
University of Florida - Davie
Philip Busey, firstname.lastname@example.org
June 9, 2009
Chemistry is a science of matter dealing with composition, structure, properties, and
transformations of matter as we commonly know it, that is, the substance of physical
objects that we can sense directly around us such as liquids, solids, and gases. One way to
define matter is, “anything that occupies space and has mass.” Matter as we know it is
composed of particles called atoms which cannot be easily created or destroyed and it is the
relations of different kinds of atoms that are the main area of chemistry.
In contrast to chemistry, physics is a more fundamental science of matter dealing with the
nature of matter, and force, motion, and energy, and all kinds of matter not just atoms but
particles smaller than atoms, and kinds of matter that do not form objects or substances as
we commonly know them.
Thus while chemistry and physics both deal with aspects of matter and energy, chemistry
deals more with the external relationships of and between material substances, while
physics deals more with what’s under the dashboard.
Atoms, elements, molecules, and compounds
The atom is a particle that is the basic unit of substances, and it is the smallest unit into
which a substance can be subdivided. An atom is a generally stable particle which consists
of a positively charged dense central nucleus containing at least one proton and sometimes
one or more neurons, around which is a negatively charged cloud of electrons. The element
is a type of element, determined by the number of protons in the nucleus of the atom, which
vary from one for the smallest type of atom, hydrogen, to 92 for the largest and heaviest
naturally occurring element, uranium. The atomic number of hydrogen is 1 and that of
uranium is 92.
Even though the number of protons is the same for all atoms of an element, the number of
neutrons can vary within certain numbers.
For example, hydrogen naturally has either zero
or one neutron.
The simple hydrogen called has only one proton in the nucleus and has the
atomic weight of approximately 1.
Since the neutron weighs about the same as a proton, the
type of hydrogen with one proton and one neutron has an atomic weight of 2.
forms are called “isotopes” hydrogen-1 and hydrogen-2 and they are commonly designated
with a superscript,
H. Two common isotopes of uranium include uranium-238 or