Y8 Timeline of Atomic Model Development

What did Democritus propose about everything in the world?

• It was made of four elements: earth, wind, water, and fire.

• It was made up of tiny, indivisible particles surrounded by empty space.

• It was made of uniformly packed spheres of positive matter.

• It was made of a dense, positively charged nucleus with electrons orbiting it.

What did Aristotle believe matter was made of?

• Tiny, indivisible particles.

• Four elements: earth, wind, water, and fire.

• Electrons and a nucleus.

• Positive and negative charges.

What did John Dalton conclude about common substances?

• They always broke down into different elements in varying proportions.

• They were made of four fundamental elements.

• They always broke down into the same elements in the same proportions.

• They contained a central nucleus.

What significant particle did J.J. Thomson discover in 1897?

• The proton

• The neutron

• The electron

• The nucleus

How did J.J. Thomson describe atoms in his "chocolate chip cookie" model?

• As mostly empty space with a dense nucleus.

• As electrons orbiting a nucleus at fixed energy levels.

• As uniformly packed spheres of positive matter filled with negatively charged electrons.

• As particles that behave like waves.

What did Rutherford's gold foil experiment reveal about atoms?

• Atoms are solid, indivisible spheres.

• Atoms consist largely of empty space with a concentrated nucleus.

• Electrons orbit the nucleus in fixed paths.

• Electrons are uniformly dispersed throughout a positive sphere.

What was a key feature of Niels Bohr's planetary model of the atom?

• Electrons are randomly scattered within a positive sphere.

• Electrons orbit the nucleus at fixed energy levels and distances.

• Electrons cannot be precisely located.

• Atoms are indivisible.

What did Werner Heisenberg's Uncertainty Principle state about electrons?

• Their exact position and speed can both be determined simultaneously.

• They orbit the nucleus in predictable paths.

• It is impossible to determine both their exact position and speed simultaneously.

• They are always found at fixed energy levels.