radioactivity P4 Flashcards
(56 cards)
Describe 2 ideas that John Dalton developed about the atom
- agreed with Democritus that matter was made up of tiny spheres ( atoms ) that could not be broken up
- believed each element was made up of a different type of “atom”
Name JJ Thomson’s model and his theory
- his measurements of charge and mass showed that an atom must contain even smaller negatively charged particles called electrons
- created plum pudding model
Features of the plum pudding model ( 3 )
- An atom is a ball of positive charge with electrons embedded in it
- It has no empty space
- The mass is spread out in the plum pudding model
What experiment did Ernest Rutherford conduct?
The alpha particle scattering experiment = he fired positively charged alpha particles at an extremely thin sheet of gold
If the plum pudding model was correct, what should have happened in the alpha particle experiment but what actually happened?
If PPM was correct = expected to pass straight through
Result = most passed straight through, but more were deflected than expected
Explain the two results of alpha experiment ( 4 marks )
Most alpha particles passed straight through the gold foil so the mass of the atom is concentrated in the nucleus
Some alpha particles were deflected so the atom has a positively charged nucleus
Describe Rutherford’s model in terms of space
an atom is mostly empty spaxe
What did Bohr’s nuclear model claim?
that electrons orbit the nucleus in fixed shells at fixed distances
What did James Chadwick prove the existence of?
the neutron = which supported understanding of isotopes
Evidence from further experiments changed the model to have a nucleus made up of ?
protons with the same positive charge, adding up to the overall charge of the nucleus
Describe the current model of the atom ( 4 features )
- most of the mass is concentrated in the nucleus
- nucleus contains protons and neutrons, meaning the nucleus has an overall positive charge
- rest of the atom is mostly empty space
- negatively charged electrons orbit the nucleus in fixed shells at fixed distances from the nucleus
What is the rule for atoms?
number of protons = number of electrons
What can electrons do within energy levels?
electrons in energy levels can move within the atom - if they gain energy by absorbing EM radiation they move to a higher energy level which is further from the nucleus
- if they release EM radiation, they move to a lower energy level that is closer to the nucleus
Describe ionisation
Very occasionally, one of the outermost electrons could absorb so much energy that it is able to completely leave the atom. This leaves the atom with more protons than electrons, causing the atom to become a positively charged ion rather than an atom
What is the atomic number?
the number of protons in an atom
What is the mass number?
the number of protons and neutrons in its nucleus
Define isotopes
Atoms with the same number of protons but different numbers of neutrons
What do all elements have?
different isotopes, but there are usually only one or two stable ones
What happens to the unstable isotopes? Name of process?
they tend to decay into other elements and give out radiation as they try to become more stable = this process is called radioactive decay
What do radioactive substances do?
they spit out one or more types of ionising radiation from their nucleus ( alpha, beta, gamma )
When isotopes decay, what else can they release?
neutrons
Define ionising radiation
radiation that knocks electrons off atoms, creating positive ions
Describe what alpha particles are made up of and what this is the same as?
- made up of 2 protons and 2 neutrons
- this is exactly the same as the nucleus of a helium atom, so we normally represent alpha particles with helium’s nuclear symbol
What do alpha particles NOT have and what does this mean?
any electrons = so have an overall charge of 2+ from those two positive protons
