Atomic Model History

Question 1

Democritus

Answer 1

Came up with idea of an uncuttable atom (wrong)

Question 2

Aristotle

Answer 2

Challenged Democritus so nobody thought about atoms for 2,000+ years

Question 3

John Dalton

Answer 3

First model.
- “all matter is made up of small particles called atoms which can’t be divided into smaller pieces”
- atoms of each element are identical and each element has different properties
- atoms of different elements combine in specific proportions to form compounds (law of definite proportion)
- atoms are not changed in chemical reactions, they are reorganized (law of conservation of mass)
His model showed a billiard ball with a solid sphere.

Question 4

Models

Answer 4

change over time as a result of experiments. laws do not change

Question 5

JJ Thompson

Answer 5

used cathode ray tubes to show that atoms were divisible. he reasoned that since atoms are neutral and they can release negative entities in a discharge tube, they must have positive stuff too?????

Plum pudding

• showed that an atom was divisible
• shows a +ve cloud with many electrons inside
• no concentration of mass
• first model of representation of atom

Question 6

Ernest Rutherford

Answer 6

• Ernest Rutherford directed highly energetic, positively charged alpha particles at a very thin gold foil
• alpha particle has 2 protons and 2 neutrons. it is an isotope of Helium called Helium-4
• he traced the particles before they hit the foil and concluded that the only configuration for an atom was all of mass and positive charge located in the middle and that electrons orbited the small nucleus
• it did not show how the electrons were moving nor where they were located
• he discovered the nucleus

Question 7

Niels Bohr

Answer 7

• Niels Bohr refined the Rutherford model
• now we know that you can’t trace an electron, you can only have a general idea of where it is
• he came up with energy shells

Question 8

modern atomic model

Answer 8

• the modern atomic model (quantum model) shows atom as a nucleus surrounded by black dots of possible places where the electron can be found.

Question 9

limitations of dalton’s model

Answer 9

• atoms are made of smaller parts like protons neutrons and electrons
• not all atoms of element are identical aka neutrons

Question 10

cathode ray tube

Answer 10

YIKES

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Question 11

bohr rutherford

Answer 11

• nuclear model

- nucleus contains protons and neutrons with electrons around it in energy shells