3.2/3.3 Electrons and Nuclei Flashcards
What was Thompson’s depiction of the atom?
Electrons are small negative charges that are distributed about a positively charged medium like plums in a plum pudding.
The negatively charged electrons would balance out the positively charged medium so that each atom would be of neutral charge.
What was Rutherford’s gold foil experiment?
He established atoms have nuclei
His experiment consisted of firing alpha particles at a very thin sheet of gold.
Alpha particles consist of two protons and two neutrons (helium atom).
Most of the alpha particles were hardly deflected at all, they passed through the foil as if empty space.
Some even bounced back!
What results were found from the gold foil experiment?
Most of the alpha particles pass straight through.
1/8000 scattered more than 90 degrees.
What was concluded from the gold foil experiment results?
Most of the atom is empty space.
Small, positive nucleus (containing most of the mass)
Electrons in space around nucleus.
How was the proton discovered?
Alpha particles fired and combined with nitrogen.
Fired at a thin sheet of metal which alpha particles absorbed through.
Causing flashes of light on zinc sulphide screen.
Transmutation-nitrogen turned into oxygen.
Oxygen was halted at the thin sheet of metal.
Meanwhile, positive particle (proton) was causing zinc sulphide screen to become positively charged.
Discovered in a magnetic field.
What is the formula of proton discovery?
Alpha particle + Nitrogen - Oxygen + Proton
What were the two dark spaces called?
Faraday and Crooke’s dark space.
What is it called when electrons are freed from a heated cathode?
Thermionic emission.
How were electrons discovered?
Maltese cross experiment- in a cathode ray tube.
When powered the cathode emits “rays” which cause phosphor coated screen to glow.
Maltese cross in the path of the “rays” block them resulting in a shadow.
This tells us that the rays travel in a straight line.
If you put a magnet near the side of the tube the shadow moves which shows that the ray paths are deflected by a magnetic field.
The rays are in fact electrons emitted from the cathode and accelerated through holes in the anode towards the screen.
How was the neutron discovered?
Berylium, when bombard with alpha particles, emitted a very energetic stream of radiation.
This stream was originally thought to be gamma radiation.
Wrong- unlike gamma rays, the unknown stream was extremely penetrative and neutral, they did not discharge electroscopes.
It was discovered that when a beam of this radiation hit a substance rich in protons (wax), protons were knocked loose which could easily be detached by the geiger counter.
This is because they have similar masses.
What are the masses of protons and neutrons?
Proton: 1.63 x 10 to the power of -27 kg
Neutron: 1.65 x 10 10 to the power of -27 kg
What is the equation for neutron discovery?
Alpha particle + Beryllium - Neutron + Carbon-12
What are nucleons?
Protons and neutrons.
What is proton number Z?
Defines the element and the number of protons and neutrons.
What is nucleon number A?
Defines a particular isotope of the element.
