Atomic Structure Flashcards
What is the mass number?
The top number which tells you the protons and neutrons.
What is the atomic number?
The bottom number which tells you the number of protons. (also electrons)
Charge of Proton, Neutron and Electron:
P - +1
N - 0
E - -1
Mass of Proton, Neutron and Electron:
P - 1
N - 1
E - 1/1860
How many electrons can fit in the shells?
2,8,18
How are protons and neutrons held together?
By strong nuclear forces which are stronger than electrostatic forces of attraction between the protons which overcomes the repulsion.
What are isotopes?
Atoms with the same number of protons but different neutrons = different mass number.
Do isotopes still react the same way?
Yes because they have the same electron configuration.
How did the atoms develop?
5
Robert Boyle - said there were substances that couldn’t be simpler.
John Dalton - discovered atom
Henri Becquerel - discovered radioactivity which shows there are particles inside atoms.
- J J Thomson - plum pudding model.
- Ernest Rutherford - alpha scattering
How did the arrangement of the electrons develop? (4)
- Neil Bohr, like a tiny solar system, electrons orbit nucleus.
- Erwin S electrons have same properties as waves, Quantum Mechanics discovered which predicts behaviour of sub atomic particles.
- James Ch - discovered Neutron.
- Lewis - modern ideas about bonding and how ions we’re formed.
What is Carbon Dating?
It is a way to find out the age of a carbon- based material up to 60,000 years old.
One well known radioactive carbon isotope is…
Carbon-14 with a half life of 5730 years and is produced by cosmic ray activity in the atmosphere.
Does the level of Carbon-14 stay the same?
Yes because all living things give out and take in carbon so it stays the same. Once it dies though, the radioactive carbon breaks down and the radioactivity falls.
Carbón-14 half life is:
5730.
What do scientists use the half life for in a material which has carbon?
Scientists use this half life to work backwards so they work out how long it has taken for the level of radioactivity to fall from what it is in a living organism to what it is in the sample.
What is the Mass Spectrometer?
The most useful instrument for the accurate determination of relative atomic masses.
What happens in the time of flight mass spectrometer?
Basically the substances in the sample are converted to positive ions, accelerated to high speeds and arrive at the detector.
The whole mass spectrometer apparatus is kept under…
A high vacuum to prevent the ions that are produced colliding with molecules from the air.
What is the first stage in the time of flight mass spectrometer?
Ionisation. There are two types:
- electron Impact
- electro spray ionisation.
What happens in Electron Impact?
The sample is vaporised and high energy electrons are fired at it from an electron gun - this knocks one electron of each particle forming a positive ion.
What happens in Electrospray Ionisation?
The sample is dissolved in a volatile solvent and forced through a fine hollow needle connected to the positive terminal of a high voltage supply which produces tiny positively charged droplets.
What is the second stage in the time of flight mass spectrometer?
Acceleration - the positive ions are attracted towards a a negatively charged plate and they accelerate towards it.
Where do the ions pass through in the negatively charged plate?
A hole in the plate, forming a beam and they travel along this flight tube to a detector.
What happens at the ion detector?
The lighter ones arrive first as they have higher velocities - flight times are recorded and the positive ions pick up an electron from the detector causing a current to flow.
The signal from the detector is passed…
To a computer which generates a mass spectrum.
