1.1 - atomic structure Flashcards
1
Q
isotopes?
A
- atoms with same number of protons but different number of neutrons.
- similar chemical properties because they have the same electronic structure
- varying physical properties because they have different masses
2
Q
relative mass of an electron?
A
1/1840
3
Q
what does a mass spectrometer do?
A
- determine all the
isotopes present in a sample of
an element and to therefore
identify elements
4
Q
why does a mass spectrometer need to be under a vacuum?
A
- otherwise air particles would ionise and register on the detector
5
Q
what are the 3 steps in a mass spectrometer?
A
- ionisation
- acceleration
- detection
6
Q
what is electron impact ionisation used for?
A
- elements and substances with low formula mass as it can cause larger organic
molecules to fragment
7
Q
stages of electron impact ionisation?
A
- a vaporised sample is injected at low pressure
- an electron gun fires high energy electrons at the sample
- this knocks out an outer electron
- forming positive ions with different charges
8
Q
what is electrospray ionisation used for?
A
- for larger organic
molecules as the softer conditions of this technique mean
fragmentation does not occur
9
Q
stages of electrospray ionisation?
A
- sample dissolved in volatile solvent + injected through hypodermic needle
- tip of needle attached to positive terminal of high voltage power supply
- particles gain H+ ion
10
Q
what happens in the acceleration stage?
A
- positive ions are accelerated by an electric field to a constant kinetic energy
11
Q
how to calculate mass of an ion in KG?
A
mass number/ 1000/ 6.022 x 10(23)
12
Q
what happens in the detection stage?
A
- sample attached to negative plate
- current is generated that is proportional to the abundance
13
Q
what is the kinetic energy equation?
A
KE = 1/2 x mass x (velocity)2
14
Q
velocity equation?
A
distance/time
15
Q
definition for relative atomic mass?
A
average mass of an atom of an element relative to 1/12th the mass of a C12 atom
