All atoms of the same element are identical in mass and size.

Atoms can neither be created, destroyed, nor divided into smaller particles.

All matter is made of small particles called atoms.

Dalton’s atomic theory was the first to describe all matter in terms of atoms and their properties.

John Dalton (1766–1844) was a British teacher and a scholar, credited for the development of atomic theory to explain about the new way of matter: Postulates of Dalton’s atomic theory:

Einstein, Heisenberg and Quantum Mechanics.

Ernest Rutherford’s hypothesis – Rutherford’s Atom model.

He provided evidence for atoms and developed atomic theory.

The Greek philosopher Democritus introduced the idea of the atom in 1800. Laws are constant, but theories may change as new facts become available. Theories are explanations of observations that are supported by reliable evidence. Laws do not provide explanations of concepts they simply state what happens. In science, laws are descriptions of events, patterns, or relationships that have been observed over and over again. What is the difference between a theory and a law? The various descriptions of matter and how it behaves is called the atomic theory. But for thousands of years, people described the nature of the matter in very different ways. Today, we know that everything is made of huge numbers of tiny particles. The ancient atomic theory was first proposed in the 5th century BC by the Greek philosophers Leucippus and Democritus and was further revived in the 1st century BC by the Roman philosopher Lucretius. He believed all substances like air, water, earth, and fire were made of small amounts of these four elements of matter.

He thought that all materials on earth were not made of atoms. He argued that matter was subdivided into indivisible particles.Īristotle, the most respected philosopher of the day, agreed with the theory proposed by Empedocles. However, Democritus believed that atoms were uniformly placed, solid, hard, incompressible, and indestructible element that moved in infinite numbers through empty space until stopped. He called this piece ‘atomos’, from which we get the word ‘atom.’ The various descriptions of matter and how it behaves is called the atomic theory.Įmpedocles, a Greek scientist and philosopher, made one of the first attempts to explain matter 2500 years ago, claiming that matter was composed of four ‘elements’-earth, air, wind, and fire-in varying quantities.Īnother Greek scholar, Democritus, countered this theory with one of his own, reasoning that any substance, when cut into smaller and smaller pieces, would eventually be cut into a piece that could not be divided further. But for thousands of years, people described the nature of matter in very different ways. Today, we know that everything is made up of huge number of tiny particles. Scientists who put forward the explanation of atomic theory: The number of protons in an atom is called the atomic number.

Electrons occupy specific orbital or energy level in the circular path around the nucleus. Negatively charged species surround the nucleus with one or more electrons. Positively charged species are made up of protons and neutrons. Atoms have tiny, positively charged and negatively charged species.

Atoms are composed of particles, including protons, neutrons, and electrons.

Development of the atomic theory