The Atom

The Atom

Aristotle – the four basic elements

-Earth-Air-Water-Fire

Democritus-Follower of Leucippus-An Atomist-Coined the word atomos meaning uncuttable or the smallest particle of matter

2000 years laterJohn Dalton – School Teacher

Five main points of Dalton's atomic theory-The atoms of a given element are different from those of any other element; the atoms of different elements can be distinguished from one another by their respective relative atomic weights.-All atoms of a given element are identical.-Atoms of one element can combine with atoms of other elements to form chemical compounds; a given compound always has the same relative numbers of types of atoms.-Atoms cannot be created, divided into smaller particles, nor destroyed in the chemical process; a chemical reaction simply changes the way atoms are grouped together.-Elements are made of tiny particles called atoms.

Daltons Model of the Atom

Cathode Ray Tube

Plum Pudding Model of the AtomJJ Thompson

Gold Foil Experiment – Ernest Rutherford

Rutherford’s Model of the Atom

Particle SymbolRelative Charge Mass (kg)

Mass Number Location

electrone- -1 9.109x10-31 0Around Nucleus

proton p+ +1 1.673x10-27 1Nucleus

neutron n0 0 1.675x10-27 1Nucleus

Atomic Number: The number of protons in the nucleus of an atom

Mass Number: The total number of protons and neutrons on a nucleus

Atomic NumberSymbolAtomic Mass

Isotope: Atoms of the same element that have different masses