The discovery of the nucleus Flashcards
Whos discovered the electron, when, and what was discovered about atoms from this?
J.J Thomson in 1911
every atoms contained at least one
What was Thomson idea about the atom?
Thomson though the atom could be like a ‘currant bum’ - with electrons dotted in the atom like currants in the bun
the positive charge was supposedly spread throughout the atom like the dough of the bun
What did Rutherford know about alpha radiation? How did he use this?
consisted of fast moving positively charged particles
he used this type of radiation to probe the atom
How did Rutherford set up the experiment?
used a narrow beam of alpha particles, all of the same KE
in an evaciated contrainer
detected by a detector which could be moved round at a constant distance from the point of impact of the beam
Why did the alpha particles need to be the same speed?
slow alpha particles would be deflected more than faster alpha particles on the same initial path
Why must the contianer be evacuated?
alpha particles would be stopped by air molecules
Why must the source of alpha particles have a long half-life?
otherwise later readings would be lower than earlier readings due to radioacitive decay of the source nuclei
Rutherford used a microscope to observe the pinpoints of light emitted when alpha particles hit the atom of the flurescent screen, what did his measurements show?
- most atoms passed straight through the foil
- 1 in 2000 were deflected
- 1 in 10 000 were deflected through angles of more than 90 degrees
What were Rutherfords conclusions?
most of the atom’s mass is concentrated in a small region, the nucleus, at the centre of the atom
the nucleus is postively charged because it reples alpha particles (which carry positive charge) that approach it too closely
How does greater deflection occur?
the electrostatic force of repulsion between the alpha particle and the nucleus increases with decreased separation
