1 - Atomic Structure Flashcards
Relative Atomic Mass
average mass of one atom of an element / 1/12th of the mass of a carbon-12 atom
An average of the mass of all the different isotopes of an element depending on the abundance of that isotope
Mass Spectrometer
Used to identify compounds and samples based on their RAM
Looks at molecules in detail
Used in forensics to identify illegal drugs
Time of Flight Spectrometer (High Impact Electron Gun)
1) Electron gun bombards sample with high energy electrons that hit the sample and knock electrons out, creating positive ions
2) Positive ions accelerated by electric field
3) Drift area allows sample to move in order to separate depending on mass size
4) Positive ions hit a detector which produces a current, positive ions gain an electron so they become unionised
size of current = abundance
Factors affecting ionisation Energies
Nuclear Charge (charge of the nucleus)
Atomic Radius
Shielding
Electron Spray Ionisation (Soft Method)
1) Sample dissolved in volatile solvent (methanol or water)
2) Sample passed through a fine hypodermic needle held at 4000V
3) Particles gain a proton from the solvent as they leave the needle
4) Fine mist/ aerosol of highly charged droplets is sprayed
5) Tip of needle is attached to high voltage power supply
6) Positive ions accelerated as they are attracted towards the negative plate
First Ionisation Energy
Energy required to remove one mole of electrons from one mole of atoms in a gaseous state
Ionisation Energy (2nd, 3rd, 4th…)
Energy required to remove one mole of electrons from one mole of ions in a gaseous state
Electron Configuration
1s2
2s2
2p6
3s2
3p6
4s2
3d10
4p6
Mass of electron
1/1836
Mass Number (A)
Number of protons plus neutrons
Always has to be whole number
(Z is symbol for atomic number)
Ionisation Energies down a group
Decrease as you go down a group
Atomic radius increases
Increased shielding effect
Ionisation Energies across a period
Increase as you go across period
Increase in nuclear charge but similar amount of shielding
Anomalies:
Phosphorus to Sulphur (electron pair)
Magnesium to Aluminium (3p)
Factors Affecting Ionisation Energy
Nuclear charge
Atomic radius
Shielding effect
Electron pair
Second ionisation energy Group 1
Very high because electron is very close to nucleus
Why 2nd IE greater than 1st IE
Electron is being removed from ion
Electron Impact vs Electro Spray
Electron Impact
-elements and substances with low formula mass
Electro Spray
-larger, organic molecules
-softer method means fragmentation is less likely to occur
How spectrometer shows abundance and and mass
Flight time:
Mass
Size of current:
Abundance
