Timeline of Atomic ModelsEarly ideas about atoms:

2500 years ago (~400 BC) Democritus Matter could NOT be divided forever Eventually the smallest piece would be

obtained ATOMOS = “uncuttable”

Timeline of Atomic Models To Democritus, atoms were small,

hard particles that were all made of the same material but were different shapes and sizes.

Atoms were infinite in number, always moving and capable of joining together.

Theory ignored for 2000 years!

Timeline of Atomic ModelsDalton’s Model of the Atom (~1800)

Elements are composed of atoms. Atoms of the same element are exactly alike. Atoms of different elements are different. Compounds are formed by the joining of atoms

of two or more elements.

Timeline of Atomic ModelsThomson (~1900)

Foundation of Modern Chemistry Some particles smaller in atom “Plum Pudding” model▪ Positive substance = pudding▪ Negative electrons = raisins

Timeline of Atomic ModelsRutherford (1911)

Positive Center = Nucleus Negative electrons around it

Timeline of Atomic ModelsBohr + Wave Model (1913)

Each electron in a specific energy level Electrons move in orbits around nucleus. Energy level = certain distance from

nucleus. Impossible to determine exact location

of electron Probable location based on energy

electron has.

Timeline of Atomic ModelsBohr + Wave Model (1913)

Orbital = Electron Cloud Electrons with the lowest energy are

found in the energy level closest to the nucleus

Electrons with the highest energy are found in the outermost energy levels, farther from the nucleus.

Timeline of Atomic Models

X X XWave X X XBohr

X XRutherford XThomson

XDalton XGreek

Electron Cloud

OrbitNucleusElectronIndivisible