ATOMIC THEORY
Brief history of the atom (Democritus and the Greek Philosophers)
Before we discuss the experiments and evidence that have, over the years, convinced scientists
that matter is made up of atoms, it’s only fair to give credit to the man who proposed “atoms” in
the first place. About 2,500 years ago, early Greek philosophers believed the entire universe was
a single, huge, entity. In other words, “everything was one.” They believed that all objects, all
matter, and all substances were connected as a single, big, unchangeable “thing.”
One of the first people to propose “atoms” was a man known as Democritus. He had an
alternative idea from the beliefs of Greek philosophers,for him he suggested that tiny,
indivisible, solid objects make up all matter in the universe. He referred to this tiny ,indivisible
objects as ‘atomos’ or ‘atomon’ .
Other Greek philosophers disliked Democritus’ “atomos” theory because they felt it was illogical.
Dalton’s Atomic Theory
A scientist by the name John Dalton, used scientific experiment to try and prove that Democritus
theory was correct . In his experiments he noted that every time he carried out a chemical
reaction, substances reacted in fixed ratios in which elements would react to combine.
Dalton suggested that subtances were composed of small, indivisible quantities which he called
“atoms” . (In reference to Democritus’ original idea)
Dalton used this idea to generate what is now known as Dalton’s Atomic Theory which stated
the following:
1. Matter is made of tiny particles called atoms.
2. Atoms are indivisible (can’t be broken into smaller particles). During a chemical reaction,
atoms are rearranged, but they do not break apart, nor are they created or destroyed.
3. All atoms of a given element are identical in mass and other properties.
4. The atoms of different elements differ in mass and other properties.
5. Atoms of one element can combine with atoms of another element to form “compounds” –
new, complex particles. In a given compound, however, the different types of atoms are always
present in the same relative numbers.
