P4 - Forces Flashcards
(36 cards)
How has the model of the atom changed over time
- 1804 John Dalton agreed the atom was made up of tiny spheres (atoms) which couldnt be broken up. He also believed each element was made up of a different atom.
- 1897 - J.J Thompson discovered particles called electrons could be removed from the atom Thompson suggested atoms were spheres of positive charge with tiny negative electrons stuck in them *like fruit in plum pudding) therefore the plum pudding model
- 1909 - Ruthfords lab tried firing a beam of alpha particles at thin gold foil. This was the scattering experiment
History of the atom
From the plum pudding model it was expected the particle to go straight through, or be slightly deflected. However some came back. Something the plum pudding model couldnt conclude or explain. The scientists realised most of the mass must be concentrated at the centre of a tiny nucleus. The nucleus must have a positive charge as it repelled the positive alpha particle. They also realised that most of the atom would therefore just be an open spave. This was the first nuclear model.
Conclusion of timetable of the atom
1804 - John Dalton - tiny spheres (atoms) couldnt be broken up. Each element = different atom.
1897 = J.J Thompson - plum pudding model
1909 - Rutherford and alpha particles - gold foil experiment.
1913 -Bohr in rutherford’s lab made current model
What is EM radiation
Electromagnetic radiation
What happens to an electron if the atom it is in releases EM radiation
The electrons move their location within the atom
Who provided evidence to suggest the existance of the neutron
James Chadwick
Do atoms have an overall charge
Yes - positive
What happens to an atom if it loses one or more of its electrons
The ion becomes a positively charged ion
What is the atomic number
The bottom number to the left of the element symbol
What is the mass number
The top number to the left of the element symbol
What number defines what elenent an atom is
The atomic number (bottom)
What is an isotope
Different variations of the same element. Same atomic number, but different mass number
Are isotopes usually stable
There are many isotopes to each element, usually only one or two are stable.
What is radioactive decay
Radioactive decay is when unstable isotopes decay into other elements and give out radiation as they try to become more stable.
What may be emitted during radioactive decay
Radioactive substances
What are the types of ionising radiation. Give their ionising power and range in air
Types : alpha, beta, gamma
Alpha (a) = strongly ionising but only travel a few cm.
Beta (b) = moderately ionising a few metres range in air
Gamma (y) = weakly ionising but can travel long distances through air
Why can alpha radiation not be used to check the thickness of metal sheets
Because they can be absorbed by a single sheet of paper. They dont penetrate very far into substance
What type of nuclear ldecay doesnt change the mass or chargeof nucleus
Gamma (y)
What is the activity of a source and its units
The rate at which a source decays Bequerels Bq (where 1 Bq is 1 decay per second)
Define half - life
Half - life is the time taken for the number of radioactive nuclei in an isotape to halve
True or false?
A short half - life means a small proportion of atoms are decaying per second
False
What are the dangers of a radioactive source with a long half-life
Nearby areas can be radioactive for many years. Sometimes millions of years
How would you find the half life of a source if you had a graph with its activity over time
Find the time on the bottom axis corresponding to a halving of the activity on the vertical axis (i.e 800 to 400)
Define radiation dose
Radiation dose is the risk of harm to body tissue due to exposure to radiation. Measured in sievers (Sv)
