Saturday, June 9, 2012


Elements are fundamental units of matter, which have characteristic properties. The periodic table contains the elements. Of the 111 known elements, 92 occur in nature, the rest are of synthetic origin. Examples of elements are oxygen, carbon and  iron.
Atoms: the smallest constituent part of an element is an atom. There are smallest particles, which are parts of an atom. The proton (positively charged) and neutron (uncharged) particle are located in the nucleus of the atom. In the shells (orbits) around the nucleus, the electron, a negatively charged particle is found.\
Atoms of one element can combine with atoms of another element to form a compound. For example, water contains two atoms of hydrogen and one of oxygen (H2O).
Molecule: Chemical elements exist as molecules, a basic unit, which can be made up of atoms of one or more elements. Thus we have a molecule of oxygen (O2) with two atoms of oxygen, while sodium chloride (NaCl) contains one atom of sodium and one atom of chlorine.
Ion: An electrically charged atom, group or molecule is called an ion. A positively, charged ion is called a cation, and negatively charged one an anion, K+   is an example of a positive atom and Cl-   is a negative atom; potassium chloride (KCl) is a neutral compound.
Isotopes: Some elements have isotopes, that they exist in two forms, with two different atomic weight; for example, the atomic weight of carbon is 12, its isotope has an atomic weight of 14 (14C ). The 14C isotope of carbon is naturally radioactive.
  Acids, Basics, pH: A chemical compound, which when dissolved in water yields hydrogen ions (H+), is an acid. There are two types of acids, inorganic acids and organic acids. Hydrochloric, sulfuric and phosphoric are  inorganic acids. Organic or carboxylic acids contain one or more carboxyl groups (COOH) in their molecule. Fatty acids and amino acids are important organic acids in nutrition.
Hydrogen ion concentration is the amount of hydrogen ion (H+)  per unit volume of an aqueous (water) solution. It is referred to as pH.
Some Chemical reactions: Some chemical reactions, occur in biological systems, are listed here.
  1. Salt formation: When an acid and a base react, salt is one of the products formed.
HCl + KOH = KCl + H2O
Acid + base        Salt + Water
2. Ester formation: When an organic acid reacts with an alcohol, an ester is formed. When a fatty acid reacts with glycerol, a fat ( an ester) is formed.
3. Oxidation-reduction: Oxidation is always accompanied by a reduction, in which electrons are transferred from one atom to another. The atom that gives up the electron is oxidized, the one that receives the electron is reduced. Thus ferric ion is reduced by vitamin C to ferrous form.
Fe+++ + reduced form of vit. C 
      Fe++ + oxidized form of vitamin C
4. Hydrolysis: The reaction of water with another compound, with uptake of a molecule of water, is known as hydrolysis. The breakdown of carbohydrates and fats in digestion is an example of hydrolysis.
5. Phosphorylation: Is a chemical reaction in which a phosphate group is introduced into an organic compound. The formation of ATP from ADP is an example of this reaction.
6. Synthesis: When a complex substance is formed from simpler substances by a series of reactions it is known as synthesis. Synthesis of proteins from amino acids is a good example of this reaction.
7. Degradation: Complex substances are gradually broken down to simpler ones. The breakdown of glycogen to glucose is an example of degradation reaction.

No comments:

Post a Comment