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Atomic Structure (Fundamental Particles (Neutron (0 (Neutral), Mass=1,…
Atomic Structure
Fundamental Particles
Neutron
0 (Neutral)
Mass=1
Found in the Nucleus.
Electron
-1 (Negative)
Mass= N/A
Found in the outer shells of the atom.
Proton
Found in the Nucleus.
Mass=1
+1 (Positive)
Mass Number
Atomic Number (Z) = Number Of Protons in the Nucleus
Mass Number (A) = Number of Protons+ Number of Neutrons
Isotopes
Time Of Flight (TOF) Mass Spectometry
Step 2- Acceleraion
The positive ions are accelerated using an electric field so that they all have the same kinetic energy
Given that all the particles have the same kinetic energy, the velocity of each particle depends on its mass.
Lighter particles have a faster velocity
Heavier particles have a slower velocity
Step 3- Flight Tube
Lighter ions travel faster and reach the detector in less time than the heavier particles that move slower and take longer to reach the detector.
eg Ions of the three isotopes of magnesium (24Mg+, 25Mg+, 26Mg+) will travel at different speeds through the flight tube and separate, with the lightest ion (24Mg+) reaching the detector first.
The positive ions travel through a hole in the negatively charged plate into a tube. The time of flight of each particle through this flight tube depends on its velocity which in turn depends on its mass.
Step 1- Ionisation
:explode:
Electron Impact (AKA Electron Ionisation)
:explode:
The sample is first vaporised. Fom an "electron gun" (A hot wire filament wih a current running though it that emits electrons), high energy electrons are fired ast the sample. This usually knocks off on lectron from each aprticle forming a 1+ ion.
X(g) + e- --> X+(g) +2e-
The 1+ ions are then attracted towards a negative electric plate where they are accelerated.
This technique Is used for elements and substances with low formula mass - can be organic/inorganic molecules.
Electrospray Ionisation
The sample is first dissolved in a volatile4 solution (eg. Water, Methanol), and then injected through a fine hyperdermic needle to give a fine mist.
The tip of the needle is attached to the positive terminal of a high-voltage power supply.
The positive charge in the needle gives the partices in the sample an extra proton- forming positive ions.
X(g) + H+ --> XH+(g)
The solvent evaporates away while the XH+ ions are attracted towards a negative plate where they are accelerated.
Step 4- Detection
The positive ions hit a negatively charged electric plate. When they hit the detector plate, the positive ions are discharged by gaining electrons from the plate.
This generates a movement of electrons and hence an electric current that is measured.
The size of the current gives a measure of the number of ions hitting the plate.
Can be used to:
Find the abundance and mass of each isotope in an element allowing for determination of its Relative Atomic Mass.
-Find the relative molecular mass of substances made of molecules.
Calculations
Volumetric Calculations
Solid
Mass(m) in grams
Molar Mass(M) in grams
In solution
Number of moles (n) = Concentration (c) in moldm3 * Volume (v)in cm3
Relative Abundance
(% On mass spectrogram
Relative atomic mass given) +(% On mass spectrogram
Relative atomic mass given)
100
Electron Configuration
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, 8s.
First ionisation energy
the energy required to remove one mole of the most loosely held electrons from one mole of gaseous atoms to produce 1 mole of gaseous ions each with a charge of 1+.
X(g)---> X+(g) + e-
Number of moles (n) =
