7.19 understand that a chain reaction can be set up if the neutrons produced by one fission strike other U-235 nuclei

During nuclear fission, a slow-moving neutron gets absorbed by the nucleus of a U-235 atom. When this occurs, the atom splits into 2 daughter nuclei, whilst also releasing a small number of nuclei. If these nuclei his other uranion-235 atoms, these atoms will split and release more nuclei. The process will repeat. this is known as a chain reaction.

7.18 understand that the fission of U-235 produces two daughter nuclei and a small number of neutrons

In nuclear fission, a slow moving neutron gets absorbed by the nucleus of an U-235 atom. This causes the atom to split. The nucleus will split into two smaller 'daughter' nuclei and will also 'spit out' a small number of neutrons.

NOTE: When uranium-235 splits into two daughter cells, these cells will be radioactive as they will have the 'wrong' number of neutrons in them. They will also be lighter elements than uranium.

7.17 understand that a nucleus of U-235 can be split (the process of fission) by collision with a neutron, and that this product releases energy in the form of kinetic energy of the fission products

Nuclear power stations get there energy from a process of splitting atoms by collision with a neutron(as this releases energy). This is how...

If a slow moving neutron will get absorbed by an atom of uranium-235 (it will absorb into the nucleus). When this happens, the U-235 nucleus will split and spits out a small number of neutrons as it does.

This process releases energy (kinetic) and is converted into heat energy in the reactor by collisions with other atoms.

7.15 describe the results of Geiger and Marsden's experiments with gold foil and alpha particles

In an attempt to disprove the plum pudding model, Geiger and Marsden set up an experiment in which  they positioned a sheet of gold foil in a circle of zinc sulphide screen. They then aimed alpha particles at a sheet of thin gold foil. They concluded that most of the alpha particles went straight through the foil, and gave a tiny flash (a scintillation) when they hit the zinc sulphide screen. However, some of the alpha particles were deflected at 90º to the direction they were traveling, and some came straight back. This concluded that inside an atom there must be positively charged nuclei which repel the alpha particles (this is why they 'bounce off' at different directions).