ELEMENTS OF MATTER
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.
- 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.
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