Radioactivity Flashcards
Plum pudding model
Thompson suggested that atoms were spheres of positive charge with tiny negative electrons stuck in them
Rutherford’s model
They fired alpha particles through a gold sheet.
Most particles went straight through
Some were deflected
Few were deflected the way they came
Most of the mass is a the centre
Atom is empty space
Nucleus is positive as it repelled positive alpha particles
Current model of an atom
An atom is a positively charged nucleus surrounded by negatively charged electrons
what happens in beta plus decay?
how does it affect the mass number and atomic number?
a proton changes into a neutron and a positron
it does not change the mass number
the atomic number decreases by one as it has one less proton
what happens in beta minus decay?
how does it affect the mass number and the atomic number?
a neutron changes into a proton and an electron
the mass number doesn’t change
the atomic number increases by 1 as it has one more proton
what happens in alpha decay?
how does it affect the mass number and atomic number?
it loses two neutrons and two protons
the mass number decreases by 4
the atomic number decreases by 2
what happens when a neutron emits a neutron?
the mass number decreases by 1
the atomic number stays the same
what is the alpha sign?
x 4 at top 2 at bottom
what is the beta minus sign?
B 0 at top -1 at bottom
what is the positron sign?
B 0 at top 1 at bottom
what is the neutron sign?
n 1 at top 0 at bottom
do gamma rays change the charge or mass of the nucleus?
the mass and atomic number stay the same
what is an atom?
a positively charged nucleus, consisting of protons and neutrons, surrounded by negatively charged electrons, . all of the mass is in the nucleus
what do the shells in an atom show?
the energy levels
what happens to an inner electron if it absorbs electromagnetic radiation?
can move up to a higher level- when it does move up I moves to an empty or partially filled shell
what then happens when the electron has moved shells?
it will quickly fall back to its original energy level, and will emit the energy it absorbed- which will be carried away by em radiation
how do atoms form positive ions when they lose an electron?
if an outer election absorbs enough energy it can leave the atom - It is now a free electron and the atom has been ionised
the atom is positive because it has more protons than electrons
what is an isotope?
are atoms of the same element with the same number of protons but a different number of neutrons
what is an Alpha particle?
two neutrons two protons
they are strongly ionising
what can stop alpha particles?
few cm of air and thin piece of paper
what is a beta minus particle?
a fast moving electron
moderatley ionsing
what is a beta plus particle?
a fast moving proton
moderatley ionisng
what can stop beta minus particles?
few metres of air and a sheet of 5mm thick aluminium
what are gamma rays
em radiation
weakly ionising
