ATOMIC THEORY Contributions of Dalton, Thomson and

ATOMS!

WHAT IS ALL MATTER MADE OF?

THINK PAIR SHARE

On your own, draw the model of a hydrogen atom. Can you draw an oxygen atom using the same model? Don’t forget to label your diagrams.

Pair up with two of your classmates and share your models of hydrogen and oxygen. Did you all come up with the same picture? Or is it different? Come up with one model of each hydrogen and oxygen as a group.

Share your model with the whole class!

BOHR MODEL OF AN ATOM

P = 1N = 0

Hydrogen Atom

Nucleus (holds protons and neutrons)

Electron Shell (holds electrons)

BOHR MODEL OF AN ATOM

P = 8N = 8

Oxygen Atom

HOW WAS THE ATOMIC MODEL DEVELOPED?

DALTON’S ATOMIC MODEL

DALTON’S ATOMIC MODEL Postulate 1: All matter is made up of small particles called atoms.

Postulate 2: An element consists of an atom of one type only.

Postulate 3: Compounds consist of atoms of more than one element.

Postulate 4: Atoms can not be created or destroyed in a chemical reaction.

Element

Compound

THOMSON’S ATOMIC MODEL

Thomson discovered the electron in 1897.

He said that negatively charged particles called electrons are submerged in a positive region.

To explain his model, he compared it to plum-pudding where the pudding is the positive region and electrons are raisins submerged into in a positive region.

Thomson called his model the “plum-pudding” model.

RUTHERFORD’S ATOMIC MODEL

Discovered the nucleus of an atom

How?

RUTHERFORD’S SCATTERING EXPERIMENT

Source of 𝛂 - particles

Detector

Gold-Foil

𝛂 - particle is He2+ ion

According to Thomson’s model, the beam of alpha particles would have gone straight through the gold atoms with little to no deflection.

The result of scattering experiment was far from what was expected. Most of the alpha particles went straight through, but some were deflected. This proved that the atom had a positive core (nucleus).

JAMES CHADWICK

In 1932, it was discovered by Chadwick that the nucleus is composed of neutronsand protons.

Neutrons have a charge of 0 and protons have a charge of +1

BOHR ATOMIC MODEL

Electrons live in fixed rings around the nucleus called shells

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ACTIVITY – PHET SIMULATION Rutherford’s Scattering Experiment Simulation

https://phet.colorado.edu/sims/html/rutherford-scattering/latest/rutherford-scattering_en.html