Atomic structure Flashcards
Isotopes
same no of protons but different no of neutrons
Electron impact
- Vapourised sample injected at low pressure
- Electron gun fires high energy electrons at sample
- Knocks out an outer electron
- Forming +ve ion with different charges (Ti—>Ti+ +e-)
Electrospray ionisation
- sample dissolved in volatile,polar solvent
- Injected through fine needle gives aerosol
- tip of needle high voltage ,gains proton(H+)
- MH+ ion moves towards negative plate
Acceleration
Positive ions are accelerated by an electric field
velocity dependant on mass
Flight tube
Positive ions with smaller m/z values ahve the same kinetic energy as those with larger m/z values & will move faster
Detection
Ions reach detector and generate a small current which is fed to a computer for analysis
Relative atomic mass
Isotope mass x % percentage abundance/ 100
Forming ions
Loose 4s before 3d
Cr and C u
Only 4s 1 in 4s shell
First ionisation energy
enthalpy change when 1 mole of gaseous atom forms ! mole of gaseous ion with a positive ion
Second ionisation energy
enthalpy change when one mole of gaseous ions with a single positive charge forms one mole of gaseous
ions with a double positive charge
Factors affecting ionisation energies
- Attraction of nucleus
- The distance of the electrons from nucleus
- Shielding of the electrons from nucleus
Why is there a small drop from Mg to Al ?
Al is starting to fill a 3p shell where as Mg has its outer electron in 3s sub shell.3p easier to remove less sheilding
Why has Na a much lower first ionisation energy that
Neon?
Na will have its outer electron in a 3s shell further from the nucleus and is more shielded.easier to remove & lower first ionisation energy
Why is there a small drop from form P to S shell?
S has 4 electron the 4th is filling doubly the 1st
slight repulsion by the negatively charged electron making the 2nd easier to remove
Why is there a general increase in the 1st ionisation energy?
down the group,outer electrons are found further from the nucleus and more shielded.
lower attraction of the nucleus
Why does helium have the largest first ionisation energy?
1st electron is on the first shell closest to nucleus & has no shielding effect from the inner shells
