Atomic Structure. 4. Flashcards
What happened in 1804
John Dalton agreed with Democritus that matter was made from atoms that could not be broken and each element was made from a different type of atom.
What happened 100 years after 1804
J.J Thompson discovered electrons could be removed from atoms.
Thompson said their were elcectrons tuck in a mass of positive charge and mad the “plum pudding model”
What happened in 1909- Alpha Scattering
Scientists in Rutherfords lab fired a beam of alpha particles to a thin sheet of gold foil - the alpha scattering experiment, from the PP model they expected to pass straight through or only be slightly defected instead most did pass through but some deflected back the reverse direction.
What did they realise in The Alpha Scattering Experiment?
Nearly all the alpha particles passed through most of the atom was empty space.
Positivley charged nucleus surrounded by a cloud of negative electrons.
Most the mass of an atom must be concentrated in the nucleus.
What did Niehls Bohr say?
Electrons orbiting the nucleus do so at a distance called energy levels.
Then James Chadwick developed the idea of the neutron whichh explained the imbalance between the atomic and mass numbers.
Give the charge of a proton neutron and electron
P= +1 N = 0 E = -1
Give the mass of a proton neutron and electron
P= 1 N = 1 E = 0.0005
What happens is electrons gain EM radiation
They move to higher energy levels
If they release EM radiation they move to lower energy levels.
How does an atom become a positive ion
If one or more of the outer electrons leave
What is an isotope
Atoms with the same number of protons but a different number of neutrons
What do unstable isotopes do
decay into other elements and give out radiations as they try to become stable. This is called radioactive decay.
What is ionsing radiation?
knocks of electrons on atoms creating positive ions
What is alpha radiation
an alpha particle is emmited from a nucleus a charge of +2
What is the alpha particles structure
two protons and two neutrons a helium nuclei
How far do alpha particles penetrate
Dont penetrate very far into materials and are stopped quickly
What are alpha particles stopped by?
A few cm of air
absorbed by a sheet of paper
Are alpha particles ionising
yes strongly because of their density.
What is a beta particle
fast moving electron released by the nucleus hae virually no mass and a charge of -1
Are beta ionising
moderatly
How penetrating are beta
moderately far into material before colliding and have a range in air of a few metres
What is beta stopped by
a few metre of air
absorbed by 5mm of aluminum foil
What happens when a beta particle is emmited
a neutron in the nucleus has changed to a proton
What are gamma waves
Electromagnetic radiation released by the nucleus
How far does gamma penetrate
pass through rather than collide with atoms
eventually they hit something and do damge