atomic structure Flashcards
what is the mass number
the protons and neutrons
what is the atomic number
the number of protons in the nucleus
what is an isotope
isotopes are atoms with the same number of protons and different number of neutrons
what is the difference between isotopes and there atoms
they have similar chemical properties due to the fact they have the same electron arrangements
but slightly different physical properties due to their varying masses
what does the mass spectrometer do
can be used to identify all the isotopes present in a sample of an element and therefore identify elements
why does a mass spectrometer need to be a vacuum
if it was not a
vacuum air particles would ionise and register on the detector
what is the first step in a mass spectrometer and what are the two ways of doing it?
ionisation where the atoms are turned into positive ions. there are two ways of doing this: electron impact and electron spray ionisation
how does electron impact work
first a vaporised sample is injected at a low pressure
then an electron gun fires high energy electrons at the sample
this knocks out an outer electron
forming positive ions with different charges
how does electron spray ionisation work
the sample is dissolved in a volatile polar solvent.
it is then injected through a small needle giving a fine mist or aerosol
the tip of the needle has a high voltage and at the tip of the needle the sample gains protons H+
finally the solvent evaporates away and the positive ions move towards the negative plates
what happens in stage two of a mass spectrometer
in stage two the ions accelerate by the electric field to a constant kinetic energy which can be worked out my
KE=1/2mv^2
what changes the velocity of different particles
since all the particles have the same kinetic energy this means that the only thing that can effect the velocity is the mass. this means the lighter masses have a higher velocity and the heavier mases have a slower velocity
what is the third stage in a mass spectrometer
the third stage is the flight stage where the particles move thought the vacuum with the same kinetic energy but different speeds and so separate depending on there mass. the ions are distinguished by their different flight times.
time of flight= length of flight tube x velocity of particle
what is the fourth and final stage of a mass spectrometer
ions reach the detector and generate a small current which is fed to a computer for analysis. the current is produced from electrons transferring from the detector to the positive ions. the size of the current is proportional to the abundance of the species.
what is the relative atomic mass
weighted average of all the isotopes of an element
the average mass of one atom of that elemt/ 1/12 of carbon 12
(isotope mass x relative abundance or % abundance) / 100
what has mass spectrometer been used for in space
to identify elements on other planets. elements on other planets can have a different composition of isotopes.
when is electron impact used in mass spectrometer vs when is electron spray ionisation
electron impact is used for substances with a lower formular mass as if it is larger it can caused it to fragment and electron spray is used for higher formular masses as it is gentler and wont cause fragmentation.
how do you measure the Mr of a molecule when it has gone through electron impact in mass spectrometer
when molecules get hit with electron impact ionisation it will often cause the molecule to fragment and so give a series of peaks on the mass spectrum caused by the fragments. the highest peak however will be caused by the full molecule as it will have not fragmented and so you can figure out the Mr from that. this peak is called the molecular ion.
how do you measure the Mr of a molecule when it has gone through electron spray ionisation
if a molecule is put through electron spray ionisation then it will not fragment. so their will be one speak equal to the MR of the ion. if you want the MR of the molecule it will be necessary to subtract one as it gained one extra proton at the start.
how is the a level atom arranged
electrons are arranged in energy levels number 1 at the nucleus and 2,3,4.. outwards.
these energy levels are split into sub energy levels named s, p, d, f
these sub energy levels are split into orbitals which each hold up to two electrons off opposite spin
what can the different sub energy levels hold
s- holds up to two electrons
p-holds up too 6 electrons
d- holds up to 10 electrons
f- holds up to 14 electrons
what is an orbital
an orbital represent the mathematical probability of finding an electron at any point within certain spatial distributions around the nucleus. 95% chance of finding an electron
what is a s orbital shaped like
a circle
what does a p orbital look like
a infinity sign
what is the exception to the rules with orbitals
4s comes before 3d
