P4 Developing the Model of the Atom (page 195) Flashcards
What was the name of the person, and the year who started Devloping the Model of the Atom?
It started with a Greek fella called Democirtus in the 5th Century BC.
He thought all matter, whatever it was, was made of of identical lumps called “atomos”, and thats as far as it got until the 1800’s.
In 1804 John Dalton agreed with Demoncritus that matter was made up of tiny spheres (“atoms”) that couldn’t be broken up, what else did John Dalton think regarding the elements?
He also reackoned that each element was made up of different type of “atom”
Nearly 100 years after John Dalton agreed with Demoncritus, J J Thomson discovered what regarding particles?
J J Thoson discovered particles called electrons that could be removed from atoms. (So Dalton’s theory wasn’t quite right).
Thomson suggested atoms were spheres of positive charge with tiny negtive electrons stuck in them like fruit in a plum pudding - The plum pudding model.
In 1909 scientists in Rutherford’s lab tried firing a beam of alpha particles (see page 196) at thin gold foil, what was this experiment called?
The alpha scattering experiment.
When Rutherfords lad done the Alpha scattering experiment, what was the outcome?
Using the plum pudding model, they expected the particles to pass straight through the gold sheet, or only be slightly deflected, but although most of the particles did go straight through the sheet, some were deflected more than expected, and a few were deflected back the way they had come - something the plum pudding model couldn’t explain. (see picture 1 on page 195)
What is the Plum Pudding Model?
It al also known as Thomson’s plum pudding model.
The plum pudding model depicts the electrons as negatively charged particles embedded in a sea of positive charge. (the structure of Thomson’s atom is analogous to plum pudding, an english dessert)
(depict means represent by a drawing, painting or other art form)
Explain why a few Alpha particles were deflected back from the alpha scattering experiment?
scientists realised that most of the mass of the atom must be concentrated at the centre in a tiny nucleus. And this nucleus must also have a positive charge, since it repelled the positive alpha particles
What else did scientist realise apart from atoms having a nucleus during the Alpha Scattering Experiment?
They realised that because nearly all the alpha particles pass straight through the gold sheet, that most of an atom is just empty space. This was the first nuclear model of the atom. (see picture 1 on page 195).
Rutherford replaced the Plum Pudding Model with what model?
The Nuclear Model, which developed into the current model of the atom (see picture 2 on page 195).
Why was the Nuclear model made, and explain what it is?
The Nuclear model resulted from the alpha particle scattering experiment, a positively charged nucleus surrounded by a cloud of negative electrons.
What did Niels Bohr say about electrons orbiting the nucleus?
He said that electrons orbiting the nucleus do so at certain distances called energy levels.
(his theoretical calculations agreed with the experimental data (see picture 2 on page 195).
Evidence from further experiments changed the Nuclear Model to include what?
further experiments changed the model to have a nucleus made up of a group of particles (Protons) which all had the same positive charge that added up to the overall charge of the nucleus.
About 20 years after the idea of a nucleus was accepted, in 1932, James Chadwick proved the existence of what?
the existence of the Neutron, which explained the imbalance between the atomic and mass numbers (see page 196).
Explain what the nucleus of an atom is?
The nucleus is tiny but it makes up most of the mass of the atom.
It contains protons (which are positively charged) they have a charge of +1 relative charge) and neutrons (which are neutral, with a relative charge of 0) - which gives it an overall positive charge.
What is the radius of a Nucleus up to the atom?
its radius is about 10 000 times smaller than the radius of the atom.
