1. simple structure of an atom
1.1. it consists of 3 parts
1.1.1. neutron
1.1.1.1. it is almost equal to the mass of a proton
1.1.1.2. it is present in the centre of the atom called the nucleus
1.1.1.3. they do not have any specific charge; it is neutral
1.1.2. protons
1.1.2.1. the mass of 1 proton is taken as one amu
1.1.2.2. it is positively charged
1.1.2.3. it is present in the centre of the nucleus
1.1.3. electrons
1.1.3.1. the mass of an electron is 1/1837 times the mass of a hydrogen atom
1.1.3.2. electrons are regarded weightless
1.1.3.3. they are negetively charged
1.1.3.4. electrons revolve around the nucleus
1.1.3.4.1. it has been found that
1.2. nucleus
1.2.1. it is the centre of the atom
2. definition
2.1. an atom is the smallest unit of an element and may or may not have its independent existence
3. modern concept of molecules
3.1. it is of two kinds
3.1.1. a cluster of atoms having the same elemnt
3.1.2. a cluster of atoms having different elements
3.2. definition
3.2.1. it is the smallest unit of matter which always has its independent existence and retains complete physical and chemical properties
3.3. atomicity of molecules of an element
3.3.1. monoatomic molecules
3.3.2. diatomic molecules
3.3.3. triatomic molecules
3.3.4. polyatomic molecules