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periodic table of elements
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ELEMENTS

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

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

Representative 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

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:

  1. Classification elements into groups with similar properties.
  2. 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.

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. 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:

  1. Atomic weight (From 1.00794 to 262.12)
  2. Atomic number (From 1 to 107)
  3. Atomic symbol
  4. Name of the element
  5. Oxidation states
  6. 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).