Knowt
Atomic Structure
Development of the Model of the Atom
Atomic Theory
Everything is made from tiny little/small particles that can’t be broken down and is separated by empty space.
The idea was unchanged until the 1800’s by John Dalton
He suggested that atoms were solid spheres and different types of spheres could make make up different elements
Thompson Model
His experiments showed that atoms couldn’t be solid spheres.
Must’ve contained negatively charged particles
A ball of positive charge with electrons embedded in it.
It was the Plum Pudding Model
Rutherfords Model
He experimented with Positive alpha particle fired at a thin sheet of gold, which should’ve passed through because the weak positive charge wouldn’t be strong enough to affect them.
Some of the particles were deflected to the side and some were deflected.
The nuclear model suggested that all of the positive charge was in the nucleus and that negative charge was around it.
The theory suggested that the atom should collapse into itself.
Bohr Model
He suggested that electrons orbited the nucleus in shells
The orbiting of electron prevents that atom from collapsing in.
He also discovered that protons made up the nucleus
Chadwick suggested neutral particles, neutrons in the nucleus
Atomic Structure Isotopes and Electron Shells
Periodic table
Bottom left is the atomic number which is the amount of protons
Top left is the mass number which is the number of protons and neutrons
Isotopes
Atoms with the same number of protons but different number of neutrons
Only one or two of an elements are stable, unstable isotopes decay into other elements by emitting radiation.
Ionisation is when an electron is lost and the atom because a positive ion.
Ionising radiation is being able to knock electrons off
Electrons
Electrons can absorb electromagnetic radiation and jump to a higher energy level/ shell. In these cases we say that the electron has become ‘excited’.
Alpha, Beta and Gamma Radiation
Unstable isotopes undergo radioactive decay which is when they emit something to change and become stable
Radioactive materials are materials that consist of unstable isotopes that can decay.
Alpha Particles
Made from 2 protons and 2 neutrons, like helium
Don’t contain any electrons so have an overall charge of 2+
They are easily stopped by collisions and can’t penetrate very far into other materials
Travel a few cm in air and can’t penetrate a single sheet of paper.
Strongly Ionising so they can easily knock electrons off of any atoms they collide with
Beta Particles
They are made from one electron and have a charge of -1 and no mass.
The electrons aren’t emitted from shells.
Beta Particles source is a neutron decays into a proton and electron.
Protons stays in the atom but the electron is emitted out at high speed.
It is moderately ionising and penetrating.
It is stopped by a few metres of air and 5mm of aluminium.
Gamma Rays
They are waves of electromagnetic radiation.
It is often emitted after alpha or beta radiation
No mass or charge means pass they can pass through materials
They are weakly ionising but can penetrate long distance. They are stopped by thick lead and concrete to stop
Emission of a Neutron
Too many neutrons in a nucleus which makes it unstable it can kick out a neutron to increase stability.