Flashcards in R6 - Alpha Scattering And Nulcear Equations Deck (12):
What happened in 1804?
- John Dalton agreed with Democritus that matter was made of tiny sphere ("atoms") that couldn't be broken up
- He reckoned that each element was made up of a different type of "atom"
What happened 100 years later?
- J J Thomson discovered that electrons could be removed from from atoms (so Daltons theory wasn't quite correct)
- Thomson suggested that atoms were spheres of positive charge with tiny negative electrons stuck in them like plums in a plum pudding
Why didn't the "plum-pudding" theory not work?
- In 1909 Hans Geiger and Ernest Marsden tried firing alpha particles at thin gold foil.
- Most of the particles went straight through and where detected when they hit the zinc sulfide screen and gave off a tiny flash of light. The odd alpha particles came straight back which was a shock
Who came up with the nuclear model of the atom?
Ernest Rutherford, boss of Geiger and Marsden, uses their results to come up with it
If the plum pudding was right, what should happen to the alpha particles?
They should pass straight through the gold foil
What was concluded from the fact that some of the alpha particles bounced back?
Inside the atoms there must be small positively charged nuclei which repel the passing alpha particles
What does Rutherfords model of the atom show?
- Most of mass concentrated at the centre
- Most of an atom is empty space
- Nucleus must be small since since very few alpha particles are deflected by much
- The nucleus must be positive to repel the positively charged alpha particles
The faster an alpha particle travels...
The less it will be deflected by a nucleus
The more positively charged a nucleus is (the higher the atomic number)...
The more an alpha particle will be deflected
The closer an alpha particle passes to the nucleus...
The more it will be deflected
What do you need to remember when your balancing a nuclear equation?
The total atomic number and mass number has to be equal on both sides