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===Properties of the Subatomic Particles===
: The [[particle]]s that make an [[atom]] all have slightly different properties. Since the particles are so small their [[mass]] and [[Electrical Charge|charge]] are extremely small numbers so, to make it easier, they are represented as 'relative' [[mass]] and 'relative' [[Electrical Charge|charge]] compared to a [[proton]].
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=====Plum Pudding Model of the Atom=====
: In 1897 [[J.J. Thompson]] discovered that there was a [[particle]] smaller than an [[atom]] which he named the [[electron]] after another [[scientist]] had [[hypothesis|hypothesised]] their existence. The [[electron]] was found to be around 2000 times less [[mass]]ive than a [[Hydrogen]] [[atom]]. It was later realised that these [[electron]]s were responsible for [[Electrical Current|electrical current]] in [[metal]]s.
: This led him, in 1904, to propose the [[Plum Pudding Model]] of the [[atom]] in which [[atom]]s were believed to be a solid ball of [[positive]] [[Electrical Charge|charge ]] with [[electron]]s stuck inside to give an overall [[neutral]] [[Electrical Charge|charge ]] to the [[atom]].
=====Nuclear Model of the Atom=====
: In 1909 [[Ernest Rutherford]] set two students to work on an experiment to probe the structure of the [[atom]] in the hope to determine if the [[Plum Pudding Model]] was correct.
: [[Ernest Rutherford|Rutherford's]] students [[Ernest Marsden]] and [[Hans Geiger]] fired [[Alpha Particle|alpha particle]]s, which are [[Positive Charge|positively charged]], at a very thin sheet of [[Gold]] foil to observe how the [[Alpha Particle|alpha particles]] changed direction as they went through the foil. This was known as [[Rutherford's Alpha Scattering Experiment]].
: They discovered that most of the [[Alpha Particle|alpha particle]]s went through in a straight line. A significant number were [[deflect]]ed and a very small number bounced off the [[Gold]] back towards the [[Alpha Particle|alpha]] source.
: If the [[Plum Pudding Model]] were correct then nearly all of the [[Alpha Particle|alpha particles]] should have passed straight through, unaffected, since the [[Alpha Particle|alpha particle]] is [[Positive Charge|positively charged ]] while [[atom]]s should have an even spread of [[Electrical Charge|charge]]d [[particle]]s all the way through them. There should have been no [[Electrostatic Force|electrostatic force]] to change their direction.: This showed that the [[atom]] must be mostly empty space, that most of the [[mass]] of an [[atom]] is concentrated in the centre and that the centre is [[Positive Charge|positively charged]]. This gave [[Ernest Rutherford|Rutherford]] [[Scientific Evidence|evidence]] to develop a new model of the [[atom]] which he proposed in 1911 called the [[Nuclear Model]] in which a very small [[Positive Charge|positively charged ]] [[Atomic Nucleus|nucleus]] is surrounded by [[orbit]]ing [[electron]]s.
=====The Bohr Model of the Atom=====