Atoms Flashcards
What was the idea of the plum pudding model?
an atom is a sphere of positive charge, with negatively charged electrons in it.
Who came up with the plum pudding model?
JJ Thomson
What did Ernest Rutherford do to test the plum pudding model?
They directed a beam of alpha particles at a very thin gold leaf suspended in a vacuum.
Alpha particles are a form of nuclear radiation with a large positive charge.
The vacuum is important because any deflection of the alpha particles would only be because of collisions with the gold foil and not due to deflections off anything else.
What did Ernest Rutherford find out?
most of the alpha particles did pass straight through the foil
a small number of alpha particles were deflected by large angles (> 40°) as they passed through the foil
a very small number of alpha particles came straight back off the foil
What did Ernest Rutherford conclude in the end?
The fact that most alpha particles went straight through the foil is evidence for the atom being mostly empty space.
A small number of alpha particles being deflected at large angles suggested that there is a concentration of positive charge in the atom. Like charges repel, so the positive alpha particles were being repelled by positive charges.
The very small number of alpha particles coming straight back suggested that the positive charge and mass are concentrated in a tiny volume in the atom (the nucleus). The tiny number doing this means the chance of being on that exact collision course was very small, and so the ’target‘ being aimed at had to be equally tiny.
So what did Rutherford Version of the atom look like?
A small positively charged nucleus surrounded by empty space and then a layer of electrons to fiord the outside of the atom.
How is an element defined?
Through its atomic number. An element with 17 protons will always be chlorine.
What is it called when the number of neutrons changes therefore changing the mass number of the same element?
An isotope
When an atom loses or gains an electrons what is it called?
An ion
Exfoliant what happens told the charge on atom when it loses or gains electrons?
It becomes a positively charged Ion if it loses electrons because electrons are negatively charged.
If 8t gains an electrons it becomes a negatively charged ion.
What is the Bohr atom?
He said that electrons that electrons orbited the nucleus at specific distances. He said because particular chemicals burn with certain coloured flames the pattern of energy released by electrons in the chemical reaction must be the same for every single atom in that element,
Therefore they cannot be arranged at random, but they must have fixed levels of energy within each type of atom.
How did Bohr represent his findings?
Through the ‘solar system’. model
