Atomic structure

Atomic structure

1. Models of the atom

   • After discovering the electron in 1897, J J Thomson proposed that the atom looked like a plum pudding. To explain the two types of static electricity, he suggested that the atom consisted of positive 'dough' with a lot of negative electrons stuck in it. This was consistent with the evidence available at the time: 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

2. Atoms, isotopes and ions

   • 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.

3. Radioactive decay

   • An atom’s nucleus can only be stable if it has a certain amount of neutrons for the amount of protons it has. Elements with fewer protons, such as the ones near the top of the periodic table, are stable if they have the same number of neutrons and protons. For example carbon, carbon-12 is stable and has six protons and six neutrons.

4. Uses and dangers of radiation

   • Shining visible radiation from a torch beam onto a hand, lights the hand up because the hand has been exposed to light. Exposing objects to beams of radiation is called irradiation. The term applies to all types of radiation including radiation from the nuclei of atoms. Irradiation from radioactive decay can damage living cells. This can be put to good use as well as being a hazard.

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