chemistry - Weed Science, PLS 4601c Section 7644 and Grad....

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Weed Science, PLS 4601c Section 7644 and Grad. – Prin. Of Weed Science AGR 6932 Section 9212 University of Florida - Davie http://grove.ufl.edu/~turf/weedscience/ Philip Busey, turf@ufl.edu 954-579-3932 (cell) June 9, 2009 Chemistry review 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. These two forms are called “isotopes” hydrogen-1 and hydrogen-2 and they are commonly designated with a superscript, 1 H and 2 H. Two common isotopes of uranium include uranium-238 or
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chemistry - Weed Science, PLS 4601c Section 7644 and Grad....

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