This document provides information about the structure and composition of atoms. It discusses the discovery of subatomic particles like electrons, protons and neutrons through the models of Thomson and Rutherford. It explains that atoms are very small, around 10-10 meters, and describes the shells and number of electrons in the K, L, M and N shells. Tables listing common elements and their symbols are included. The document also defines molecules as groups of atoms bonded together, and provides examples of monoatomic and diatomic molecules like hydrogen, oxygen and ozone. It introduces the concept of ions as charged particles in compounds.

2. 1.) History of the Atom.
2.) Define Atom ?
3.) About Atoms.
4.) Modern day symbols of Atoms of different elements.
5.) Atom made visible
6.) Structure of Atom
7.)Nucleus of the Atom
8.)Electrons
9.) Protons
10.) Neutrons
11.) Thomson’s model of an Atom
12.) Rutherford’s model of an Atom

10. Atoms are very small in size and smaller
than anything we can imagine or compare
with.
Atoms are measured in nanometer.
1 nanometer = 10 -9 m or 1 meter = 109 nm.
Example :- The atomic radius of an atom of
hydrogen is 10-10 m.
The radius of a molecule of water is 10-9 m.

39. Shell n 2n2 No. of electrons in
shells or orbits
K 1 2(1)2 2
L 2 2(2)2 8
M 3 2(3)2 18
N 4 2(4)2 32

49. Element Symbol Element Symbol Element Symbol
Aluminum Al Copper Cu Nitrogen N
Argon Ar Fluorine F Oxygen O
Barium Ba Gold Au Potassium K
Boron B Hydrogen H Silicon Si
Bromine Br Iodine I Silver Ag
Calcium Ca Iron Fe Sodium Na
Carbon C Lead Pb Sulphur S
Chlorine Cl Magnesium Mg Uranium U
Cobalt Co Neon Ne Zinc Zn

79. A molecule is a general group of two or more
atoms that are chemically bonded together, that
is, tightly held together by attractive forces.
A molecule can be defined as the smallest particle
of an element or a compound and is capable of an
independent existence and shows all the
properties of that substance.
Atoms of the same element or of different
elements can join together to form molecules.

80. The molecules of an element are constituted by the same
type of atoms.
Molecules of many elements, such as argon(Ar),
helium(He),…etc. are made up of only one atom of that
element.
But, this is not the case with most o the non-metals.
For example, a molecule of oxygen consists of two
atoms of oxygen and hence it is known as a diatomic
module O2(oxygen).
If 3 atoms of oxygen unite into a molecule, instead of
the usual 2, we get ozone.

81. The number of atoms
constituting a
molecule is known as
its atomicity.

82. Type of Element : Non – metal.
Name Atomicity
1. Argon - Monoatomic
2. Helium - Monoatomic
3. Neon - Monoatomic
4. Sodium - Monoatomic
5. Aluminum - Monoatomic
6. Hydrogen - Di-atomic
7. Oxygen - Di-atomic

88. Compounds composed of metals and non
metals contain charged species. The charged
species are known as ‘Ions’. An ion is a
charged particle and can be negatively or
positively charged. A negatively charged ion
is called an ‘Anion’ and the positively
charged ion is called a ‘Cation’.