chemistry 4.1 defining the atom

Using your unaided eyes , you cannot see the tiny fundamental particles that make up matter . Yet , all matter is composed of such particles , which are called atoms . An atom is the smallest particle of an element that retains its identity in a chemical reaction .

The ancient greek pre-socratic philosopher Democritus(460 BC- 370 BC) was among the first to suggest the existence of atoms , he is remembered today for his formulation of an atomic theory of the universe .

the real nature of atoms and the connection between observable changes and events at the atomic level were not established for more than 2000 years after Democritus's death . the modern process of discovery regarding atoms began with John dalton (1766-1844) , an English chemist and a schoolteacher . by using experimental methods , Dalton transformed Democritus's ideas on atoms into a scientific theory .

1-All elements are composed of tiny indivisible particles called atoms

2-Atoms of the same element are identical but the atoms of any one element are different from those of any other element .

3-Atoms of different elements can physically mix together or can chemically combine in simple whole -number ratios to form compounds

4- Chemical reactions occur when atoms are separated from each other , joined , or rearranged in a different combination . Atoms of one element , however , are never changed into atoms of another element as a result of a chemical reaction .

Atoms of the same element have the same properties because they are all made of the same kind of atoms .

Atoms are super small that if you line up 100,000,000 copper atoms side by side they would produce a line only 1 cm long!

Despite individual atom’s small size they can still be observed using instruments such as scanning electron microscopes