the atomic theories

The atomic theory has evolved over time through several key stages:

1. Dalton's Atomic Theory (1803): John Dalton introduced the first scientific atomic theory, which stated:

   • Elements are made of atoms, which are indivisible and indestructible.

   • All atoms of a given element are identical in mass and properties.

   • Compounds are formed by a combination of different atoms.

   • A chemical reaction rearranges atoms.

2. Thomson's Model (1897): J.J. Thomson discovered the electron and proposed the "plum pudding" model, the cathode ray tube experiment, suggesting that atoms were a uniform sphere of positive charge with scattered electrons.

3. Rutherford's Model (1911): Ernest Rutherford conducted the gold foil experiment, leading to the nuclear model of the atom, where most of the mass is concentrated in a small, dense nucleus, surrounded by orbiting electrons.

4. Bohr Model (1913): Niels Bohr refined Rutherford's model by introducing quantized orbits for electrons, explaining the stability of atoms and their emission spectra. higher the energy level faster the e- orbit.

Note: Chadwick discovered the neutrons.

neutron>proton>electron

• the orbits around the nucleus are labeled as n=1, n=2, n=3… or K,L,M,N…

• the n=1 orbit is called the ground state

• an electron in the ground state has the lowest energy and the greatest stability.

• the n=2 and higher states are called excited states.

• electrons in the excited states have more energy but less stability.

• more energy=greater distance from the nucleus

• an electron that absorbs energy will move to a higher orbit

• an electron that loses energy will move to a lower orbit