Atomic Structure

Atom: The smallest particle of a chemical element that can exist is called an atom. It cannot exist independently without combination with other atoms or molecules. Let us consider the element iron . All the atoms of iron are alike and when comes in contact with water and air, undergoes rusting.

Molecule: The smallest unit, consisting of a group of atoms, into which an element or a compound can be divided without a change in its chemical nature is called a molecule. A molecule can exist independently and consist of one or more than one atom of the same element. Let us consider an example: two hydrogen atom come together to form hydrogen molecule.

   Atom                                  Molecule

1. Cannot exist              1. Can exist independently.

independently.

2. May or may not         2. Stable 

react.           

3. Single atom cannot    3. Group of atoms having 

be further divided.             same or different atoms 

                                         that can be further                                                    broken up into atoms.

4. Example:                    4. Example: 

an atom of hydrogen.      two atoms of hydrogen

                                        combine to form a 

                                         hydrogen molecule.

   

Matter

Any thing that has mass and occupies space is called matter. The quantity or the amount of matter that a body contains is called its mass. Every thing around us is made up of matter.

States of matter

In nature,matter exists in three forms: solid, liquid and gas. Forms of matter are also called states of matter. There are other two states of matter in universe, i.e., plasma and bose-einestine condensate [BCE] state.

• Solid:

A solid has a definite shape and volume. It retains its shape unless it is acted upon by an external agent such as heat or a force.

For example: soil, sugar, wood, etc.

• Liquid:

A liquid has a definite volume but no definite shape. liquids take the shape of the container they are poured into.

For example: water, milk, juice, oil, etc.

• Gas:

A gas has neither a definite shape nor definite volume. most gases cannot be seen with the naked eye.

For example: oxygen, carbon dioxide, hydrogen, etc.

Periodic table

PERIDIC TABLE:

The periodic table is the arrangement of all the elements in a tabular format. it has 118 elements as of 2016. In the table, the chemical elements are arranged in order of atomic number, usually rows, so that elements with similar atomic structure appear in vertical columns. The elements are arranged in the increasing order of their atomic numbers. The periodic table has 18 vertical columns as group number from 1 to 18 and seven horizontal rows as periods. 

As per old sign convention, the 18 vertical columns were grouped into 8 groups and were represented by roman numerals.