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Fundamental concepts of Chemistry |
Compounds
A compound is a substance with a fixed ratio of chemical elements which determines the composition, and a particular organization which determines chemical properties. For example, water is a compound containing hydrogen and oxygen in the ratio of two to one, with the Oxygen between the hydrogens, and an angle of 104.5° between them. Compounds are formed and interconverted by chemical reactions. Molecules
A molecule is the smallest indivisible portion of a pure compound or element that retains a set of unique chemical properties. A molecule consists of two or more atoms covalently bonded together. Ions
An ion is a charged species, or an atom or a molecule that has lost or gained one or more electrons. Positively charged cations (e.g. sodium cation Na+) and negatively charged anions (e.g. chloride Cl−) can form neutral salts (e.g. sodium chloride NaCl). Examples of polyatomic ions that do not split up during acid-base reactions are hydroxide (OH−), or phosphate (PO43−).
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