Key Areas covered The orders of magnitude – the range of orders of magnitude of length from the very small (sub-nuclear) to the very large (distance to furthest known celestial objects).

What we will do today Describe the standard model of the atom Discuss and define different orders of magnitude from the very small to the very large

Particles and Waves Unit 2

The atom

The Standard Model of the Atom Plum pudding model of the atom: For centuries scientists have investigated what particles everything is made up of. + - In 1910, Ernest Rutherford set up an experiment: Rutherford Scattering Rutherford’s observations: Most α particles passed through without much deflection. A few α particles were deflected at a large angle. Source of α particles Gold foil α Rotating detector vacuum (a) (b)

The Model of the Atom Model of the Atom: Electrons in orbit − Negative charge Rutherford’s conclusions: The atom was mainly empty space. At the centre of the atom there was a small, highly dense, positively charged nucleus. protons Positive charge + nucleus neutrons no charge

The relative masses and charges of the proton, neutron and electron are: Particle Mass Charge Symbol Proton 1 + 1 1 p Neutron 1 n electron 1/1840 - 1 0 e -1

It is important to understand the scale of sizes scientists have studied… Powers of Ten film

Orders of Magnitude Smaller than a human, eg: Particle or object Neutrino Proton Hydrogen atom Dust Human being Order of magnitude ~10–24 m 10–15m 10–10 m 10–4 m 100 m Larger than a human, eg: Particle or object Earth Sun Solar system Nearest star Galaxy Distance to a quasar Order of magnitude 107m 109m 1013m 1017m 1021m 1026 m

Revised Higher 2012 E

2013 Revised Higher

Possible answer Rutherford’s experiment on the atom had two main conclusions: The atom is mainly made up of empty space At the centre of the atom there was a small, highly dense, positively charged nucleus. Therefore this diagram could be considered a good representation of an atom. The centre point (nucleus) is made up of protons (+ve charge) and neutrons (no charge). The electrons (-ve) are on the outer shells. The space between the nucleus and electrons would realistically be much greater. Electrons are thousands of times smaller than protons and neutrons and therefore the scale is not entirely accurate.