INTRODUCTION TO CHEMISTRY
 
Science has been classified into various branches for simplification of study. It is broadly classified into Chemistry, Biology and Physics. Mathematics is not branched as a science but considered as the basis of all science.
Chemistry may be defined as the science that is concerned with the characterization and classification of matter and the chemical transformations which it undergoes. However, this may not be an adequate definition as each new chemical concept stimulates fresh observation and experimentation leading to growing refinement as well as development of other concepts.
From the above it follows that, an understanding of chemistry starts with characterization (i.e. composition and structure) of different types of matter. As all matter (available naturally or synthetically prepared) is made up of atoms of different elements, study of elements and its atoms constitutes a fundamental branch of chemistry. The chemical behavior of matter can be explained using atomic structure as its basis. Similarly the physical behavior of matter provides information regarding molecular structure.

Chemistry is further divided into three branches :-

1.	Organic Chemistry	:	Study of carbon compounds.
2.	Inorganic Chemistry	:	Study of elements (metals or non-metals) and compounds other than those studied in organic chemistry.
3.	Physical Chemistry	:	Deals with structure of matter and the laws governing chemical reactions of organic or inorganic matter. (i.e. chemical bonding, electrolysis, gas laws, chemical thermodynamics etc.)

Introduction to the Periodic Table

The Periodic table is an arrangement of elements in the order of their increasing atomic numbers to show that elements have related properties. Earlier tables, such as those of Dmitry Mandeleev (photograph) (1869) and Lother Meyer (1869-70) were based on atomic weights which are measured as bulk properties and valency relationships. At that time the concept of atomic numbers was unknown. The main purpose of the periodic table was:

Classification elements into groups with similar properties. To predict the possibilities of new elements based on their properties.

The modern form of the periodic law states that properties of the elements are the periodic function of their atomic numbers and the properties of the elements depend on their electronic configuration.
The modern periodic table consists of arrangements of elements in three broad categories.

- metals (located on LHS) - non-metals (located on RHS) - metalloids ( in between)

Understanding the Periodic Table : The periodic table (Figure 2) arranges 109 known elements in order of their increasing atomic number. All these elements are arranged in Groups and Periods.

Groups

Periods

The vertical columns are called Groups. Eight columns 1 to 7 column further divided into 'A' and 'B' 8 t h column not divided Group zero for noble elements Elements in each group have the same number of electrons in the outer shell and hence the same valency. Identical Chemical behavior for each group elements Lower down the group, number of shells increase by 1; hence atomic radius also increases.

The horizontal rows are     called Periods. Seven rows No further division 6 t h period includes     Lanthanide series 7 t h period includes    Actinide series Each period begin with an     alkali metal. Number of electrons     increase by one, across     the period. Elements change from    metals (Na) through semi-    metals (Si-Silicon) to non-    metals (Argon-Ar). Elements change from     reducing agents (Na) to     oxidizing agents (Cl). Number of shells remain     the same; atom size (radii)     decreases.

 
ELEMENTS
An element is a pure substance that cannot be decomposed into any pure substance and which forms basic building blocks of any matter.
2.1 Classification of Elements

Class	Position in periodic table	Properties	Examples
Noble gases	Group 'O'	Gases Colorless Chemically Unreactive Diamagnetic (weakly repelled by magnetic field)	Neon Argon Krypton
Represe-ntative elements	Group 'A'	Metallic or nonmetallic Wide range of chemical behavior Range of physical characteristics Diamagnetic or paramagnetic (drawn in magnetic field )	Nitrogen Bromine Boron
Transition elements	Group 'B'	Metallic Paramagnetic Forms highly colored compounds	Titanium Iron Zinc
Inner Transition elements	Bottom of periodic table	Properties similar to elements of group III B Covered over two periods 6th and 7th 6th period elements are called Lanthanide series 7th period elements are called Actinide Series Metallic In general paramagnetic	Thorium   Terbium Curium

Diagonal Relationships :
On moving diagonally across the periodic table, the elements show certain similarities in their properties which are quite prominent in some cases as shown below. This is called a diagonal relationship.

Classification of elements on the basis of electronic configuration:
From the view point of electronic configuration the elements can be subdivided into four major sub groups (Figure 1). They can be classified as s,p,d and f block elements.

1. s-block elements : These have two atoms and include groups I A & II A. They contain one or two electrons in their outer S-orbital. Strongly electropositive metals. The group I A elements are alkali metals. Elements with two electrons in the outer orbit are called alkaline earth metals.

2. p-block elements : The elements from groups III A to VII A are included in this type. These are generally non-metals. These elements are generally non-conductors with the exception being Silicon and Germanium which are semi-conductors.
3. d-block elements : These are the elements in which the last electron is placed in d-orbital of penultimate energy level. These elements are also known as transitional elements. All are metallic and have high melting and boiling points. Good conductors of heat and energy.
4. f-block elements : The transition elements in which pre-penultimate f-sub orbital is being filled up are called as inner-transition elements. There are two series of these elements :
1) Lanthanides & 2) Actinides. Their compounds are colored and are usually paramagnetic.
5. zero-group elements : Earlier these elements were known as inert or Noble gases. They are chemically unreactive. They are incapable of forming any chemical compounds.



Reading the Periodic Table :

Figure 2 shows that each box in periodic table contains the following data:

Atomic weight (From 1.00794 to 262.12) Atomic number (From 1 to 107) Atomic symbol Name of the element Oxidation states Electronic configuration

Note the difference between the atomic number and the atomic weight. Thus element 12 is Magnesium (atomic number is 12) and not Carbon (atomic weight is 12).

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