Topic 4 - Atomic Structure Flashcards
What are the 5 stages in the development of the atom?
Dalton: Solid ball of non-divisible, very dense mass
Thompson: Plum pudding - solid ball of positive charge with small negatively charged balls within it
Rutherford: Nuclear - small and dense positive mass in the centre with surrounding negatively charged masses, mostly empty space
Bohr: Electrons held in energy shells but nucleus was indivisible
Chadwick: Neutrons and protons in the nucleus with electrons in fixed shells surrounding
Describe the alpha scattering experiment
Alpha particles, which have a positive charge, were fired at thin gold foil and their movements were measured
What were the results and how did they affect our view of the atom?
The majority of the atoms passed straight through, unaffected - most of the atom is empty space
Some were pushed off of their original path - there is a positive mass somewhere in the atom
Some were deflected - the positive mass is very small and dense
^^The plum pudding model couldn’t explain this
Why are protons and electrons directly proportional?
This is so that the overall charge of an atom is negative
What happens when protons and electrons are not equal?
The atom become a charged particles called an ion
Define an isotope
Atoms of an element with the same number of protons but a different number of neutrons
Define radioactive decay
Atoms decaying into other elements and giving out radiation as they try to become more stable
What are alpha particles?
Helium nuclei
What are beta particles?
Fast-moving electrons
What are gamma rays?
Electromagnetic waves with a short wavelength
What are the properties of alpha particles?
They are stopped very quickly, they can only travel a few cm in air and won’t penetrate and piece of paper but because of their size they are highly ionising
Define ionising
When ionising particles collide with atoms they will knock electrons off of them
What are the properties of beta particles?
They are moderately ionising and they can travel farther than alpha particles, for every beat particles emitted, a neutron turns into an electron
What are the properties of gamma radiation?
They are very penetrating and can travel long distances, they are weakly ionising as they tend to pass through atoms rather than collide with them, they will eventually do something and cause damage
What are nuclear eqautions?
A way of showing radioactive decay using element symbols
Why does the atomic number decrease by 2 but the mass number decreases by 4 when an alpha particle is emitted from an atom?
An alpha particle is a helium nucleus and whilst protons are positively charged, neutrons just have a mass no charge
What happens to the atomic number of an element when a beta particle is emitted?
It increases by 1 because an electron is negatively charged and has an atomic number of -1
What is a half life?
The time taken for the number of radioactive nuclei in an isotope to halve
T/F: radioactive substances give out radiation from the nuclei of their atoms under specific circumstances
False: radioactive substances give out radiation from the nuclei of their atoms no matter what
What does a Geiger-Muller tube and counter do?
Measures the number of counts of radiation reaching it per second
What can half lifes be used for?
- Measuring the time it takes for radiation to be emitted/the rate it takes a source to decay
- Carbon dating
Does the radioactive activity of a decaying source ever reach zero?
No. It just keeps on halving .e.g. 1/16 –> 1/32 –> 1/64 –> 1/128
Give an alternative definition of a half life in terms of activity
The time taken for the activity of a radioactive source to halve
Are sources with a longer or shorter half life more dangerous?
Sources with a shorter half life are more dangerous because they are emitting more radiation faster but sources with a long half life are still dangerous
