Topic 6- Radioactivity Flashcards
What did J.J. Thomson discover about electrons in 1897
He discovered that electrons could be removed from atoms, so atoms must be made up of smaller bits
What did J.J. Thomson suggest about atoms
He suggested the ‘plum-pudding’ model - that atoms were spheres of positive charge with tiny negative electrons stuck in them like fruit in a plum pudding
How long did the “plum pudding” model theory last
Until 1909
Who disproved the “plum pudding” model and how
Rutherford and Marsden tried firing a beam of alpha particles at thin gold foil. From the plum-pudding model, they expected the particles to pass straight through the gold sheet, or only be slightly deflected
But although most of the particles did go straight through the sheet, some were deflected more than expected, and few were deflected straight back the way they had come - something the plum-pudding model couldn’t explain
Rutherford realised this meant that most of the mass of the atom was concentrated at the centre in a tiny nucleus
He also realised that most of an atom is empty space, and that the nucleus must have a positive charge, since it repelled the positive alpha particles
This lead to the creation of the nuclear model of the atom
Who tweaked Rutherford’s idea a few years later and what did he propose
Niels Bohr and he proposed a model where the electrons were at fixed orbits at set distances from the nucleus. These distances were called energy levels
What did Neil Bohr suggest about the electron and whatsthe model called
He suggested that electrons can only exist in these fixed orbits (shells),and not anywhere in between and the model is called the Bohr model
What’s our current model of the atom like
Positively charged nucleus surrounded by negatively-charged electrons
Virtually all the mass of the atom is in the nucleus. The nucleus is tiny - about 10000 Tim’s smaller than the whole atom. The nucleus contains positively charged protons and neutrally charged neutrons. The rest of the atom is mostly empty space
The negative electrons whizz around the outside of the nucleus in fixed orbits called energy levels or shells. They give the atom its overall side of around 1x10^-10m
The atoms are neutral so the number of protons = number of electrons. This is because protons and electrons have an equal but opposite relative charge.
What happens if an atom looses an electron
It becomes a positive ion
What happens if an atom gains an electron
It becomes a negative ion
What do atoms join together to form
A molecule
What is a protons relative mass and relative charge
Relative mass is 1
Relative charge is +1
What is an electrons prelative mass and relative charge
Relative mass is 0.0005
Relative charge is -1
What is a neutrons relative mass and relative charge
Relative mass is 1
Relative charge is 0
How do electrons in an atom sit
On different energy levels (shells)
Is each energy level a different distance away from its nucleus
Yes
How can an inner electron move up to a higher energy level
If it absorbs a enough Electromagnetic (EM) radiation with the right amount of energy
What happens when an inner electron moves up an energy level
It moves to an empty space or partially filled space and is said to be ‘exited’
What happens after the electron falls back into its original energy level
It will emit(lose) the same amount of energy it absorbed. The energy is them carried away by EM radiation
As you move further out from the nucleus what happends to the energy levels
They come closer together (so the difference in energy between two levels next to each other gets smaller)
Would an exited electron release more or less energy when falling from the third energy level to the second then an exited electron falling from the second energy level to the first
Less energy will be released. So the frequency of the generated radiation decreases as you get further from the nucleus
What do changes in the nucleus itself lead to produce
The production High energy, high frequency gamma rays
What can happen if an outer electron absorbs radiation with enough energy
It can move so far that it leaves the atom. It then becomes a free electron and the atom is said to have been ionised. The atom is now a positive ion. It’s positive as there are now more protons then electrons. An atom can lose more then. One electron. The more electrons it loses, the greater it’s positive charge
What is ionising radiation
Any radiation that can knock electrons off of atoms.how likely it is that each type of radiation will ionise an atom varies
What’s an isotope
A different form of the same element. Atoms with the same number of protons but with a different number of neutrons (a different mass number)
