Atomic structure and radioctivity Flashcards
What did Democritus (500bc) proposed
that everything is made up of particles that cannot be broken dowmn any further and are separated by empty space.
What did John Dalton (1800) proposed
that these particles are solid spheres and that there are different particles for different element
What did JJ Thompson (1897) proposed
He proposed Plum pudding model: He has done a number of experiments that concluded that atoms simply cannot be solid shpeheres. (they must caontain negativly charged particles)
His model stated that atom is a ball of positive charge filled with discrete electrons
what did Ernest Rutherford (1909) proposed
He and his students have conducted a gold foil experiment. Which basically involved shooting positivly charged alpha particle at the gold foil.The prediction was that if atom is mostly positive space then the particle would go right thought, however in reality most of them deflected to the side and some even came back.
Based on these results he has suggested his nuclear model, which stated that an atom is a nucleus of positive charge that exists in a cloud of negative charge.
What is a flaw in ernest nuclear model
there was nothing that was stopping the negative cloud of electrons form rushing in to the posive nucleus therefor making whole atom collapse (which it does not)
What did neils bohhn proposed in 1913
He said that the positive nucleus remain the same but the negative atoms orbit that nuclus in shells just like planets orbit the earth.
This is important because orbiting of electrons prevents the atom from collapsing
who has discoved protons and neutrons
protons: Ernest Rutherford
Neutrons: James chandwick
what are isotopes
atoms withe the same number of protons but different number of neutrons
How does electrons move their energy levels
Electrons orbit the nucleus at specific energy levels which are also called shells
The shells get progressively further from the nucleus and increase in energy level.
Electrons can absorb electromagnetic radiation and jump to a higher energy level / shell. In these cases we say that the electron has become ‘excited’.
Excited electrons can later fall back to a lower energy level, and emit electromagnetic radiation in the process.
Electrons can also absorb enough energy to leave the atom altogether, this is known as ionisation
what is an ionising radiation
radiatin that is able to knock elecrons off atoms
what do we mean by radioactive material
consists of unstable isotopes that can decay
what are alpha particle made up of
2 protons and 2 neutrons and have 2+ charge
can alpha particle penatrate
the are relativly ralge therefore they can’t penetrate very far into other materials, in fact the can only fly few cm in the air and absorbed by a single sheet of paper
how ionising are alpha paricle
their large size can knock electrons off any atoms tehy collide with
what do beta particles consist of
a single electron so it has no mass and a charge of 1-
how ionising are beta particles
they are moderately ionising
how far do beta particles penetrate
they penatrate several metres of air and need about 5 mm of aluminium to stop them
what do gamma consists of
Gamma rays are waves of electromagnetic radiation that is ofen emmited after alpha or ebta radiation as the way for nuclues to get rid of a bit of extra energy
how ionising gamma rays are
as the do not have a charge or a mass the simply pass thought material therefor they are weakly ionising
how penetrating gamma rays are
they penetrate very far and long distance and need thick sheets of lead or multiple metres of conterete to stop them
what is an emisison of a netron
if a nucles has to muchc neutrons making it unstable it can sometimes thow out neutron to make it more stable
what do we repesent alpha by
4 2 H
how do you present alpha decay
- 4 from mass no
-2 from atomic num
