Atomic Structure Flashcards
(27 cards)
Why do isotopes have similar chemical properties
They have the same electron configuration
Why do isotopes have varying physical properties
They have different masses
Why does time of flight spectrometry need to be done in a vacuum
Otherwise air particles would ionise and register on the detector
How do you calculate R.A.M if % abundance is given
R.A.M = sum of (isotopes mass x % abundance) / 100
How do you calculate R.A.M if relative abundance is given
R.A.M = sum of (isotope mass x relative abundance) / total relative abundance
How do you calculate the mr of a molecule using mass spectrum ( electron impact ionisation)
The peak with the largest m/z (there will be multiple peaks due to fragmentation)
What is the peak with the largest m/z value on a mass spectrum called
The molecular ion peak
How many peaks will there be on the mass spectrum if electrospray ionisation was used
1 peak
How do you find the mr from the mass spectrum (electrospray ionisation was used)
Find the m/z value of the peak and take one away (the mass of the hydrogen atom)
What is the shape of s sub levels
Spherical
What is the shape of p sub levels
Dumbbell
What can a single orbital contain
2 electrons with opposite spin
Define 1st ionisation energy
The Enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge
Define 2nd ionisation energy
The Enthalpy change when one mole of gaseous ions with a single positive charge forms one mole of gaseous ions with a double positive charge
What are 3 factors that affect ionisation energy
1) the attraction of the nucleus (how many protons)
2) the distance of the electrons from the nucleus
3) shielding
Why is there a small drop in 1st ionisation energy from Mg to AI
AI has outer electrons in 3p sub shell rather than 3s sub shell. 3p electrons are higher in energy and shielding by the 3s electrons, so they’re easier to remove
Why is there are small drop in 1st ionisation energy from P to S
For S, pairing begins in the 3p orbital, which creates natural repulsion between negatively charged electrons, so electron is easier to remove
What are 4 steps in time of flight spectrometry
1) ionisation
2) acceleration
3) flight tube
4) detection
What are the 2 ways in which atoms can be ionised for TIF spec
Electrospray or electron impact
Describe electron impact ionisation
- vaporised sample is injected at low pressure
- electron gun fires high energy electrons at sample
- this knocks off an outer electron
- this forms a positive ion
Describe electro spray ionisation
- sample is dissolved in a volatile, polar solvent
- sample injected through a fine needle
- tip of needle has a high voltage
- at the tip of needle, the sample molecule gains a proton
- solvent evaporators as MH+ ions travel towards negative plate
Write an equation foe what happens in electro spray ionisation
M (g) + H+ —> MH+ (g)
Describe the acceleration step
- positive ions are accelerated by an electric field so they all have a constant kinetic energy
