Atomic Structure Flashcards
Mass of proton
1
Mass of neutron
1
Mass of electron
1/1800
Charge of proton
+1
Charge of neutron
0
Charge of electron
-1
Atomic number
number of protons in the nucleus
Mass number
Total number of protons and neutrons
Isotopes
Atoms with the same number of protons but different number of electrons
Reason mass spec is done under a vacuum
Otherwise air particles would ionise and be detected
Steps of mass spec
Ionisation, acceleration, drift, detection
Electron impact ionisation
High energy electrons are fired at a vaporised sample removing an outer electron forming positive ions
Electrospray ionisation
Sample is dissolved in a volatile, polar solvent and injected through a fine needle. The tip of the needle has a high voltage adding a proton to the sample. M(g) + H= –> MH+
Use of electron impact
elements and substances with low formula mass. Larger molecules may fragment
Use of electrospray ionisation
larger organic molecules as fragmentation is less likely
Acceleration
Positive ions are accelerated by an electric field to a constant kinetic energy = 1/2 m v2
Flight Tube/ Drift region
Lighter ions move down the tube quicker than heavier ones and are distinguished by flight times
Detection
positively charged ions are attracted to a negatively charged plate generating a current, which a computer analyses. The more ions of a particular size, the larger the current produced
Relative atomic mass
weighed average of all isotopes of an atom compared to 1/12th mass of a C-12 atom
Relative atomic mass calculation
(mass 1 x abundance 1) + (mass 2 x abundance 2) + … / total abundance
What is the relative atomic mass for Mg?
Mg-24 = 78.70%, Mg-25 = 10.13%
Mg-26 = 11.17%
24.3
Key features to include when asked for species for a peak on a mass spectrum
charge and mass number. e.g. 24Mg+
Calculate the relative atomic mass of Te. Te-124 = 2, Te-126 = 4, Te-128 = 7, Te-130 = 6
127.8
Copper has 2 isotopes 63-Cu and 65-Cu. The RAM is 63.5. What is the abundance of each isotope
63-Cu = 72.5% 65-Cu = 27.5%