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ATOMS, MOLECULES AND IONS You do not need much chemistry to understand basic physiological mechanisms but you do need to know what atoms, molecules and ions are…… An atom is a very small object indeed. There are millions of atoms in the ink that makes up this full stop . Elements are pure substances containing only one type of atom. Elements have their own shorthand symbol eg. carbon = C, Nitrogen = N etc. Here are a few common elements…. hydrogen nitrogen carbon oxygen sodium phosphorus sulphur chlorine iron calcium H N C O Na P S Cl Fe Ca A molecule is two or more atoms joined together by a chemical bond. For example, water is made up of two hydrogen and one oxygen atom and is written H2O. O O O O C O H H an oxygen gas molecule a carbon dioxide gas water is two atoms of molecule is two atoms of oxygen - O2 oxygen and one carbon atom - CO2 Some atoms and molecules carry a charge. These are called ions. Ions are very common in physiological systems, in fact you are unlikely to find some atoms and molecules in non-ionic form. Ions are very important in physiology and many processes such as nervous conduction would not work without them. Here are some common ions: sodium ion Na+ hydrogen ion H+ phosphate ion PO4 3- potassium ion K+ chloride ion Cl - hydrogen carbonate ion HCO3- calcium ion Ca2+ sulphate ion SO42- Like magnet poles, opposites attract and some oppositely charged ions bond together. An example of this is salt, sodium chloride formed by one sodium ion and one chloride ion. in water they Na+ Cl- dissociate into Na+ Cl- separate ions Positively charged ions are called cations. Negatively charged ions are called anions. Ions are soluble in water and all of the above cations and anions are found as electrolytes in body fluids.
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