Physics revision.

Physics revision.

1. Models of the atoms.

   • solids cannot be squashed, therefore the atoms which make them up must be solid throughout
   • rubbing two solids together often results in static charge so there must be something (electrons) on the outsides of atoms which can be transferred as atoms collide
   • Plum Pudding Model
     • Has a single ball of posetive charge
     • Had no nucleus
     • Has electrons in a ramdome positions

2. Atoms, Isotopes & Ions.

   • Atoms are very small, they have a radius of around 1 × 10-10 metres.
   • The modern view of the atom is of a nucleus containing protons and neutrons with smaller electrons orbiting outside the nucleus.
   • Protons and neutrons are the heaviest particles in an atom and as a result they make up most of the mass of the atom. The mass of electrons is often not considered to be significant. The number of protons is what defines the element, ie an atom with six protons in its nucleus will always be carbon, and uranium will always have 92 protons.
   • A is the mass number Z is the atomic number X is the symbol
   • Ions Normally, atoms are neutral. They have the same number of protons in the nucleus as they have electrons orbiting in the energy levels around the nucleus. Atoms can, however, lose or gain electrons due to collisions or other interactions. When they do, they form charged particles called ions
   • if the atom loses one or more electrons, it becomes a positively-charged ion if the atom gains one or more electrons, it becomes a negatively-charged ion

3. Radioactive decay.

4. Uses of dangers of radiation.