Dalton's model of an atom :
1.Elements are made of very small particles that are called atoms.
2.Atoms of a given element are similar in size, mass, shape and other properties.
The observations that led to Dalton's model of an atom :
Dalton assumed that the law of conservation of mass and law of definite proportions should be explained using the idea of atoms. SO, this led to his model of atom that matter is composed of very small particles that are called atoms and atoms of a given element are similar in size, mass, shape and other properties.