Topic 4: Atomic Structure Flashcards
How big is the radius of an atom?
1 x 10⁻¹⁰ metres
How much smaller is the radius of the nucleus compared to the nucleus of the atom?
1/10 000
What did the atomic theory (Democtritus) state? [2]
- Everything is made from tiny particles, which can’t be broken down any further
- They are separated by empty space
What did John Dalton conclude? [2]
- Atoms were solid spheres
- Different types of spheres make up the different elements
What did the plum pudding model (J.J. Thomson) state?
The atom is a ball of positive charge with electrons stuck in it
Desscribe Rutherford’s gold foil experiment and the results [3]
- Fired alpha particles at thin gold foil
- Expected particles to pass straight through or only be slightly deflected
- Although most particles passed straight through, some were deflected more than expected and some were deflcted back the way they had come
What was concluded as a result of the gold foil experiment and why? [2]
- Atoms contain a compact, positive nucleus in the centre - because some of the particles were deflected back
- Rest of the atom is empty space - nearly all of the particles passed straight through
What was the model of the atom known as after the gold foil experiment?
Nuclear model
What did Bohr add to the nuclear model?
Electrons orbit the nucleus at specific distances
What did Chadwick discover?
The presence of neutrons in the nucleus
Describe the process of radioactive decay [3]
- Some atomic nuclei are unstable
- The nucleus gives out radiation as it chnages to become more stable
- This process is random
What is activity?
The rate at which a source of unstable nuclei decays
What is activity measured in?
Becquerels (Bq)
What is count-rate?
The number of decays recorded each second by a detector
What is ionsing radiation?
Radiation that knocks electrons off atoms, creating positive ions
Alpha particle properties:
i) made from?
ii) penetration distance?
iii) stopped by?
iiii) how ionising?
i) Helium nucleus (2 protons, 2 neutrons)
ii) Don’t penetrate very far, only travel a few cm in air
iii) Can be stopped easily, e.g. paper
iiii) Strongly ionising
Beta particle properties:
i) made from?
ii) penetration distance?
iii) stopped by?
iiii) how ionising?
i) Fast-moving electron
ii) Penetrate moderately far, a few metres in air
iii) Moderately hard to stop, e.g. sheet of aluminium
iiii) Moderately ionising
Gamma particle properties:
i) made from?
ii) penetration distance?
iii) stopped by?
iiii) how ionising?
i) Waves of electromagnetic radiation
ii) Penetrate far
iii) Hard to stop, e.g. thick sheets of lead
iiii) Weakly ionising
