2-NatureOfMolecules - Intro. Biol. Course Guide Sathasivan,...

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Intro. Biol. Course Guide Sathasivan, 2005 Chap. 2. Nature of Molecules 1 2. THE NATURE OF MOLECULES Outline I. Basic Definitions and Concepts of Atoms II. Chemical Bonds and Interactions All things great and small, living and non-living, are made of simple atoms and molecules. In this chapter we will look at some basic terms related to this subject and the different types of bonds and interactions between atoms and molecules. I. Basic Definitions and Concepts Matter: A substance that takes up space and has mass. Element: A substance made up of a single atom. It cannot be broken down to other substances by ordinary chemical means. Elements are defined by the number of protons they have. Compound : Two or more different elements combined. Molecule: Two or more atoms bonded together. Atom : The unit of a matter. Atoms consist of 3 major particles. Mass (Dalton) charge Proton 1 positive Neutron 1 neutral Electron 0 negative Protons + neutrons = mass number (approximate mass) or the atomic weight (the absolute weight with reference to H or O, and it is the average of isotopic weights of an element). The number of protons in each element is unique, and it is called the atomic number . Living organisms contain about 25 elements. The 4 major elements that make up about 96 % of the living matter are C, O, H and N. The elements P, S, Ca and K make up about 3-4%. Other essential elements for life such as iron, magnesium and iodine are needed in small amounts and are called trace elements. Isotopes of an element contain the same number of protons but varying number of neutrons. 12 C = 6 protons + 6 neutrons - a stable isotope 13 C = 6 protons + 7 neutrons - a stable isotope 14 C = 6 protons + 8 neutrons - a radioactive isotope Stable isotopes can also be used for biological experiments when special methods can be used to separate molecules
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Intro. Biol. Course Guide Sathasivan, 2005 Chap. 2. Nature of Molecules 2 based on their atomic weights. Radioisotopes emit radiation due to the unstable nucleus. Some of the radioisotopes are used in biological experiments to determine the age of a
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2-NatureOfMolecules - Intro. Biol. Course Guide Sathasivan,...

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