The famous philosopher, Aristotle (388–322 BC), who also lived at that time, postulated that all matter was made of only four elements- Earth, Air, Water, and Fire. His contribution helped people with understanding the idea of an atom and helped other scientists a further look into the science of the atom and its generic makeup. Democritus created the first atomic model (a round sphere with no electrons, protons, or neutrons). To them, human reasoning was superior to experimentation. Instead, they use reasoning to back up their beliefs. Philosophers are not scientists neither do they test their ideas. He was the first person to use the word “atom”/ Life Persona. The modern atomic structure is based on s-, p-, d-, f-block elements classified on the basis of the number of electrons in the outer quantum shell or energy levels in inorganic chemistry.Greek philosopher, Democritus (460–370 BC). These factors explain the chemical properties and position of the elements on the modern periodic table. The modern structure of atoms is based on quantum numbers of electron orbitals and electron configurations. These quantum numbers are the identification numbers for electrons. Therefore, along with these two quantum numbers another two quantum numbers need to explain the fine structure of the atoms. These two quantum numbers are not sufficient to specify the fine structure of the atoms. The particles and wave properties of electrons can be explained by the de Broglie relation.īohr and Sommerfield’s theory indicated the principal and azimuthal quantum number of atoms. The angular momentum of an electron moving in an orbit is an integral multiple of h/2π.īohr’s and Sommerfield’s theories could not explain the fine structure and wave properties of atoms.From one orbit to another lower energy orbit with the emission of energy.

An electron can jump from one orbit to another with higher energy on the absorption of energy.

Therefore, this orbit or orbits is called energy level or hydrogen energy level where electron neighbor emits nor absorbed energy.

An atom possesses several stable circular orbits in which an electron can stay.

Niels Bohr proposed the structure of the hydrogen atom (one electronic atom) is called Bohr model. When a moving charged particle will emit radiation, the particle loses kinetic energy and hits the nucleus. Rutherford’s model does not conform to the classical model of electromagnetic radiation.

The nucleus of an atom is surrounded by negatively charged particles carrying negligible mass, called electrons arranged in a definite structural arrangement.

He named this part as a nucleus of an atom.

All the positive charges and the almost entire mass of an atom are concentrated in a very small central core.

Rutherford atomic model is based on the following assumption, This century Rutherford model or alpha ray scattering experiment has given valuable information about the nucleus of an atom and extranuclear electrons. Science goes step by step and every scientist depends on the work of his predecessor.

It does not explain the isotopes of elements because Dalton’s postulates state that all atoms of an element have identical masses.

It states that atoms are indivisible and indestructible parts of matter.

Dalton’s atomic theory does not account for subatomic particles such as electrons, protons, and neutrons.

A chemical reaction is a rearrangement of atoms in matter or compounds.

Compounds are formed by the combination of two or more same or different kinds of atoms.

All the atoms of a given element are identical atomic mass and properties.

All matter made up of atoms is indivisible and indestructible.

Postulates of Dalton’s atomic theoryįor learning chemistry or physics, Dalton’s atomic theory or model is based on the following postulates or assumptions, Therefore, the modern structure investigated by electronic configuration and atomic spectrum is different from Dalton’s atomic model. The most important factor in physics and chemistry for the determination of the structure has been given by the study of the electromagnetic spectrum emitted or absorbed by atoms.

Today electrons hold the key to structure and chemical bonding. The modern atomic structure clearly indicates an atom composed of subatomic elementary particles such as electron, proton, and neutron.

John dalton atomic theory