. Elements of biology, with special reference to their rôle in the lives of animals. Biology; Zoology. NATURE OF LIFE AND LIVING MATERIAL 9 Molecules: The molecule that is formed when oxygen and hy- drogen unite is water. One speaks of molecules thus formed of different types of atoms as chemical compounds. For convenience, the molecule is represented by symbols of the atoms of which it is composed, showing how many and what kind of atoms are pres- ent. Thus two atoms of oxygen form a molecule of oxygen, writ- ten O2; the water molecule is H2O; sulphuric acid is written H2SO4, being composed o
. Elements of biology, with special reference to their rôle in the lives of animals. Biology; Zoology. NATURE OF LIFE AND LIVING MATERIAL 9 Molecules: The molecule that is formed when oxygen and hy- drogen unite is water. One speaks of molecules thus formed of different types of atoms as chemical compounds. For convenience, the molecule is represented by symbols of the atoms of which it is composed, showing how many and what kind of atoms are pres- ent. Thus two atoms of oxygen form a molecule of oxygen, writ- ten O2; the water molecule is H2O; sulphuric acid is written H2SO4, being composed of two hydrogen, one sulphur, and four oxygen atoms. Any given chemical compound always contains the same constituents always in the same proportions; a molecule of water always consists of two hydrogen and one oxygen atoms. If the number of atoms is changed the characters of the compound are likewise changed. If an atom of oxygen is added to the water molecule, H2O, a new compound, H2O2, hydrogen peroxide, is formed, the characteristics of which are different from those of water. Organic Compounds: If a bit of plant or animal substance, for example, a leaf or a piece of meat, is heated in a tube not easily reached by the air, there remains a residue of black materials, largely composed of charcoal, or a crude form of carbon. This sim- ple test demonstrates that the element carbon is a conspicuous part of protoplasm. This being true, it becomes necessary to understand at least some of the characteristics of the carbon It is known that the carbon atom has four electrons on its outer shell or orbit and will accept four more, that is, it has the valence Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Buchanan, James William, 1888-. New York, London, Harper & brothers
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