The atomic theory, which holds that matter consists of small , indivisible particles in constant motion, was proposed within the 5th cent. BC by the Greek philosophers Leucippus and Democritus and was adopted by the Roman Lucretius. However, Aristotle didn't accept the idea , and it had been ignored for several centuries. Interest within the atomic theory was revived during the 18th cent. following work on the character and behavior of gases

The concept of the atom was revisited and elaborated upon by many scientists and philosophers, including Galileo, Newton, Boyle, and Lavoisier. In 1661, Boyle presented a discussion of atoms in his The Sceptical Chymist. However, English chemist and meteorologist Dalton is credited with the primary modern atomic theory, as explained in his a replacement System of Chemical Philosophy.

The smallest particle of an element that still retains its properties is atom.

The ancient Greek philosophers Democritus and Leucippus recorded the concept of the atomos, an indivisible building block of matter, as early because the 5th century BCE.

After the electron was discovered by J.J. Thomson in 1897, people realised that atoms were made from even smaller particles than that they had previously thought. However, the atomic nucleus had not been discovered yet then the “plum pudding model” was suggests in 1904. during this model, the atom is formed from negative electrons that float during a “soup” of charge , very similar to plums during a pudding or raisins during a fruit cake (Figure 4.3). In 1906, Thomson was awarded the Nobel prize for his add this field. However, even with the Plum pudding Model, there was still no understanding of how these electrons within the atom were arranged.

Rutherford administered some experiments which led to a change in ideas round the atom. His new model described the atom as a small , dense, charged core called a nucleus surrounded by lighter, charged electrons. differently of brooding about this model was that the atom was seen to be sort of a mini system where the electrons orbit the nucleus like planets orbiting round the sun. A simplified picture of this is often shown alongside. This model is usually referred to as the planetary model of the atom.

John Dalton proposed that each one matter consists of very small things which he called atoms. This wasn't a totally new concept because the ancient Greeks (notably Democritus) had proposed that each one matter consists of small, indivisible (cannot be divided) objects. When Dalton proposed his model electrons and therefore the nucleus were unknown.

Modern atomic theory begins with the work of Dalton , published in 1808. He held that each one the atoms of a component are of precisely the same size and weight (see atomic weight) and are in these two respects unlike the atoms of the other element. He stated that atoms of the weather unite chemically in simple numerical ratios to make compounds. the simplest evidence for his theory was the experimentally verified law of straightforward multiple proportions, which provides a relation between the weights of two elements that combine to make different compounds.

There were problems with Rutherford's model: for instance it couldn't explain the very interesting observation that atoms only emit light at certain wavelengths or frequencies. Bohr solved this problem by proposing that the electrons could only orbit the nucleus in certain special orbits at different energy levels round the nucleus.

Rutherford predicted (in 1920) that another quite particle must be present within the nucleus along side the proton. He predicted this because if there have been only charged protons within the nucleus, then it should forced an entry bits due to the repulsive forces between the like-charged protons! to form sure that the atom stays electrically neutral, this particle would need to be neutral itself. In 1932 James Chadwick discovered the neutron and measured its mass

Although the foremost commonly used model of the atom is that the Bohr model, scientists are still developing new and improved theories on what the atom seems like . one among the foremost important contributions to atomic theory (the field of science that appears at atoms) was the event of scientific theory . Schrodinger, Heisenberg, Born and lots of others have had a task in developing scientific theory .

• The first model of the atom (“soccer ball”) was introduced by John Dalton in early 1800. He thought of the atom as a featureless ball of uniform density.