Atoms

What is an atom?

the smallest particle of an element that retains the properties of the element

Aristotle

Four elements: water, fire, earth, air

believed everything was made up of either of these

Democritus

Said matter was made up of atomos (atoms) which were indivisible and homogeneous

Dalton’s Atomic Theory

Atoms at small, indestructible particles lacking internal structure

• solid sphere

Thomson

Pudding model: Discovered electron embedded in a positively charged sphere

Rutherford Gold-Foil Experiment

-Atom is composed of mostly empty space

-Electrons and protons are positive

James Chadwick

Identified a neutron as the subatomic particle with a mass equal to that of a proton

Modern view

-Atom is mostly empty space

-Two regions: nucleus (electrons and protons)

-Electron cloud (where you might find an electron