Development Of The Atom And Periodic Table Flashcards
Before the discovery of the electron what were atoms thought to be?
Tiny solid spheres that cannot be divided. Different types of spheres make up different elements.
What did JJ Thompson say about the atom?
They cannot be solid spheres as they must have negative particles. He created the plums pudding model
What is the plum pudding model?
A ball of positive charge with negatively charged electrons embedded in it
Who is Ernest Rutherford?
He did the alpha particle experiment
What is the alpha particle experiment?
Alpha particles were shot at a really thin piece of gold. Most went straight through, some got deflected and little came straight back
What did the alpha particle tell us?
That the atom is mostly empty space
There is a small, dense positively charged nucleus in the centre
There was a cloud of negative electrons
What was the name of the atomic model from the alpha particle experiment?
The nuclear model
Who is Niels Bohr?
He adapted the nuclear model by suggesting electrons orbit the nucleus in shells
What happened after Neil’s Bohr?
Rutherford found that nucleus was made of small particles called protons
What happened after the discovery of protons?
James Chadwick provided evidence to show the existence of neutrons in a nucleus in an atom
What was the periodic table like before the discovery of proton and etc,?
The elements were ordered by their atomic weights
What did Mendeleev find?
All elements displayed a pattern of chemical properties, he left gaps for elements that he thought had not been discovered
What was wrong with the early periodic table?
They early tables were incomplete and some elements were places in inappropriate groups. We can see this now because of our knowledge on isotopes.
What happens to the scientific model of an atom when new experimental evidence is released?
The model is either changed or replaced
