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 $jump to a higher energy leve$ l/ 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 $penetrate long distanc$ e. 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.