when was the idea of an atom first developed describe this theory
According to this idea, if one were to take a lump of matter and cut it into ever smaller pieces, one would eventually reach a point where the pieces could not be further cut into anything smaller.
Introduction
Atomic theory traces its origins to an ancient philosophical tradition known as atomism. According to this idea, if one were to take a lump of matter and cut it into ever smaller pieces, one would eventually reach a point where the pieces could not be further cut into anything smaller.
The basic idea that matter is made up of tiny indivisible particles is very old, appearing in many ancient cultures such as Greece and India. In the early 1800s. The idea that matter is made up of discrete units is a very old idea, appearing in many ancient cultures such as Greece and India.
Atom Atomic theory Atomic theory
In philosophy Introduction Philosophical atomism
The basic idea that matter is made up of tiny indivisible particles is very old, appearing in many ancient cultures such as Greece and India. In the early 1800s, the scientist John Dalton noticed that chemical substances seemed to combine and break down into other substances by weight in proportions that suggested that each chemical element is ultimately made up of tiny indivisible particles of consistent weight.  The idea that matter is made up of discrete units is a very old idea, appearing in many ancient cultures such as Greece and India. 
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Atomic theory [SEP] Introduction
Atomic theory is the scientific theory that matter is composed of particles called atoms. Atomic theory traces its origins to an ancient philosophical tradition known as atomism. According to this idea, if one were to take a lump of matter and cut it into ever smaller pieces, one would eventually reach a point where the pieces could not be further cut into anything smaller. Ancient Greek philosophers called these hypothetical ultimate particles of matter "atomos", a word which meant "uncut". In the early 1800s, the scientist John Dalton noticed that chemical substances seemed to combine and break down into other substances by weight in proportions that suggested that each chemical element is ultimately made up of tiny indivisible particles of consistent weight.