topic 1-physical chemistry

how has the atom developed over time

-thompsons plum pudding model

-rutherfords model

-bohrs model

symbol for. element, mass number and atomic number

mass number A

atomic number Z

element X

relative isotopic mass

mass of an atom of an isotope compard with 1/12th of the mass of an atom of carbon-12

relative atomic mass

the weighted mean mass of an atom of an element compared with 1/12th of the mass of an atom of carbon-12 Ar

mass spectroeter

The mass spectrometer gives accurate information about relative isotopic mass and also about the relative abundance of isotopes.

Mass spectrometry can be used to identify elements.

Mass spectrometry can be used to determine relative molecular mass

TIme of Flight (TOF) Mass Spectrometry

-this form of mass spectrometry records the time it takes for ions of each isotope to reach a detector. using this, spectra can be produced showing each isotope present.

1. ionisation

2. acceleration

3. ion drift

4. detection

5. analysis

ionisation

a sample of an element is vapourised and injected into the mass spectrometer where a high voltage is passed over the chamber. this causes electrons to be removed from the atoms (it is ionised) leaving +1 charged ions in the chamber

acceleration

these positively charged ions are then accelerated towards a negatively charged detection plate

ion drift

the ions are then deflected by a magnetic field into a curved path, the radius of their path is dependent on the charge and mass of the ion

detection

when the positive ions hit the negatively charged detection plate, they gain an electron producing a flow of charge. the greater the abundance the greater the current produced

analysis

these current values are then used in combination with the flight times to produce a spectra print out with the relative abundace of each isotope displayed.

what may happen during the ionisation process

a 2++ charged ion may be produced. This means it will be affected more by the magnetic field producing a curved path of smaller radius. as a result, its mass to charge ration (m/z) is halved and this can be seen on spectra as a trace at half of the expected m/z calue

using this spectra how can the ar be calculated

(m/z x abundance) / total abundace