1. Dalton, Thomson and Crookes
MODELS OF THE ATOM
Dalton, Thomson and Crookes

2. John Dalton (1766-1844) Dalton was the first to define an element
Element = a pure substance made up of one type of particle or atom. Each element has its own distinct properties and cannot be broken down into simpler substances by means of chemical change
Dalton’s vision of the atom is also called the “Billiard Ball” model because he thought that the atom was a solid sphere of matter

3. Dalton’s Atomic Theory
all matter is made up of small particles called ATOMS
atoms cannot be created, destroyed or divided into smaller particles
all atoms of the same element are identical in mass and size, but they are different in mass and size from the atoms of other elements
compounds are created when atoms of different elements link together in definite proportions

4. William Crookes ( )
Using a gas discharge tube, he noticed that a positively charged pinwheel (“cathode”) would rotate when an electric charge was passed through the tube
Crookes believed that this electric charge (called cathode rays) must have mass as well as motion

5. J.J. Thomson ( )
Thomson took Crookes’ work and created a new experiment
he designed an experiment to investigate how these charged corpuscles would move in an electric field
found that the corpuscles were attracted towards positively charged plates - therefore the corpuscles must be negatively charged
called them ELECTRONS

6. Protons
Thomson conducted similar experiments, this time with anode rays and negatively charged plates
anode rays were attracted to the negatively charged plates - therefore they must contain positively charged particles
Thomson called these particles PROTONS

7. Thomson’s inferences... All atoms contain both protons and electrons
all protons are identical, all electrons are identical. Electrons differ from protons
electrons have a negative charge, protons have a positive charge
an electron has the same amount of charge as a proton, even though the charges are opposite in kind.
A proton has much more mass than an electron

8. Thomson’s model of the atom
Thomson pictured the atom as a combination of protons and electrons
he thought that the electrons were embedded in a sphere or positively charged protons
looks like a blueberry muffin
called the “Blueberry muffin” model