History of the atom and periodic table and electronic structure

Who created the plum pudding model?

JJ Thomson

What led Thomson to the theory of the electron

His measurements of charge and mass showed that an atom must contain even smaller negatively charged particles

What was the plum pudding model?

it was a model of the atom showing a ball with a cloud of positive charge with electrons studded in random places

Who created the nuclear model?

Ernest Rutherford

When was the nuclear model created

1909

what was the alpha particle experiment

It was an experiment where Rutherford shot alpha particles at a piece of thin gold foil. He expected most of the particles to go straight through and a small amount to be deflected back as they thought that the plum pudding model didn't have enough positive charge concentrated in one area for it to deflect back most of the particles. Despite most going through, a lot more than expected deflected back which led to the conclusion that there was a nucleus where all the positive charge was concentrated and the rest of the atom was empty space with a cloud of electrons surrounding the nucleus

Why did Bohr believe that Rutherford's model of electrons would be incorrect?

Because if the electrons were in a cloud around the nucleus, they would become attracted to the nucleus and collapse the atom

How did Bohr come about electron shells?

Bohr believed that the electrons were in shells that orbited the nucleus at a fixed distance from the nucleus and that they were in fixed energies

How did Rutherford discover the proton?

He realised that the nucleus could be divided into smaller particles each of which had the same charge as a hydrogen nuclei and these hydrogen nuclei were later referred to as protons.

How were neutrons discovered?

James Chadwick used scattering data to calculate the mass and realised there was a missing quantity and then this later came to be the neutrons

How are electrons arranged in atoms

Electrons are arranged in shells with the first shell having a maximum of 2 electrons and every shell afterwards has a maximum of 8 electrons.

How did John Dalton arrange the elements?

In order of atomic weight

How did John Newlands build on Dalton's ideas?

He also arranged it in order of atomic mass but noticed that every eighth element seemed similar so he came up with the law of octaves but it later stopped working as he didn't leave spaces for new elements and some of the elements in his order did not have similar properties

What did Mendeleev do to the periodic table?

Mendeleev also put the elements mainly in order of atomic mass but switched some elements around so they match similar properties of those around it.

Why did Mendeleev leave gaps in his periodic table?

He left gaps to indicated elements that hadn't been discovered which allowed him to predict their properties and when these elements were discovered, they matched his predictions.

How did the discovery of isotopes confirm Mendeleev's ideas?

This is because isotopes of the same element have different atomic masses but same chemical properties which confirmed his idea of not putting all elements in a strict order of atomic mass