Maharishi Kanada suggested that

Matter was composed of many tiny particles called paramanus, which combined to form larger particles called anus.

Who called paramanu as an atom

the Greek thinker Democritus

dalton's atomic theory

He described the atom as the smallest particle of matter that still exhibits all the properties of an element.

Main features of Dalton's atomic theory

1. Matter is composed of indivisible particles called atoms. 2. Atoms can neither be created nor destroyed. 3. The atoms of an element are identical in every sense but differ from those of another element. 4. Atoms of an element can combine with atoms of another element in a fixed whole number ratio to create a molecule of a compound. 5. Many atoms of the same element can combine to form a molecule of that element 5. Atoms are the smallest particles of matter that play a role in chemical reactions.

fundamental/ sub-atomic particles

protons, neutrons, and electrons

who discovered electrons

They were discovered by JJ Thomson in 1897 while he was studying the properties of cathode rays.

structure of cathode ray tubes

The CRTs were made of glass tubes sealed on both ends with metal plates. The metal plate connected to the positive terminal of the current was called the anode, while the plate connected to the negative terminal was called the cathode. It contained a gas at very low pressure.

metal plate of CRT called cathode

connected to the negative terminal of the source of current.

metal plate of CRT called anode

connected to the positive terminal of the source of current.

cathode rays

when high voltage current was passed through the CRT, the CRT started glowing due to the emission of rays from the cathode.

which rays are made of negative particles [electrons]

Cathode rays

How did jj thomson show the negative nature of the particles in cathode rays

when an electric field was applied in the path of cathode rays in the discharge tube, the cathode rays deflected to the positive side.

properties of electrons

1. its properties are independent of the gas in the discharge tube 2. it carries 1 unit negative charge.

mass of electron

9.108 * 10^-31kg

charge of electron

1.602* 10^-19 coulombs

electron is denoted by

0 e −1 ​ with -1 being the charge and 0 being its mass.

protons were discovered by

E. goldstein, when he was performing an experiment with a discharge tube having a perforated cathode.

anode / canal rays

when an electric field was applied, rays were also emitted from the anode and passed through the perforated cathode.

Rays having positively charged particles [protons]

anode rays

properties of protons

1. positively charged particle 2. mass is 1.672 ^-27 kg 3. charge is 1.602 coulomb

pum pudding model

It was the first model of an atom suggested by J. J. Thomson. According to this model, the atom is a positively charged sphere in which electrons are embedded like plums in plum pudding.

why is an atom considered electrically neutral

because the total positive charge is always equal to the total negative charge

discovery of nucleus

in 1911, lord rutherford discovered the nucleus through the alpha particle scattering experiment.

gold foil experiment

it was the bombardment of a thin gold foil in an evacuated chamber with fast moving alpha particles.

alpha particles

they are positively charged particles that are formed when 2 electrons are removed from a helium atom. they have 2 units of charge and 4 units of mass.

observations

1. most of the particles passed straight through the gold foil without any deflection. 2. a small fraction of the particles were deflected at small angles. 3. very few of them reflected back.