SOLID SPHERE MODEL
PLUM PUDDING MODEL
NUCLEAR MODEL
PLANETARY MODEL
Atomic Models
Centuries ago, people didn’t know exactly what was inside an atom, but they had some “ideas”.
Around 400 BC, a Greek philosopher named Democritus came up with a theory that everything in
the world was made of tiny indestructible particles called “atomos”, which means “uncuttable”.
The next step in atomic theory development didn’t happen for nearly 2000 years, when British
chemist John Dalton in 1808 conducted some experiments about his Solid Sphere Model. Following
his breakthrough, Dalton proposed that everything in the world was made up of atoms—tiny
indestructible solid spheres that were unique for every element. Atoms of different elements combine
to form different compounds and are rearranged during chemical reactions.
After that, came an English physicist named J.J Thompson in 1904 and his trusty cathode ray tube.
He proposed the famous Plum Pudding Model. This model characterizes an atom as a particle that
is composed of a positively charged mass (the pudding), as well as tiny negative charges embedded
in it (like plums).
In 1911, another chemist called Rutherford proposed his Nuclear Model of an atom where most of
the atom’s mass was concentrated in a positively charged center (which he later named the nucleus)
around which the electrons orbited like planets around the sun.
After Rutherford, another chemist Neils Bohr in 1913 theorized that if an electron jumped to a lower
energy orbit, it would give out extra energy in the form of radiation, thereby maintaining atomic
stability. Even though Bohr’s model doesn’t hold true for complex multi-electron systems, his
planetary model is still the most popular representation of atomic structure in most textbooks.
The current model of the atom is the “Quantum Mechanical Model” or the “Electron Cloud Model”,
which was developed in 1926 by several scientists, including Erwin Schrödinger and Werner
Heisenberg. This model is based on quantum mechanics principles, which describe the wave
behavior of matter and energy at the subatomic level.
MODEL
PROPONENT
CONTRIBUTION TO
THE
YEAR
UNDERSTANDING
INTRODUCED
OF ATOMIC
STRUCTURE