3.1.1 Atomic Structure
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What is ionisation energy?
The energy required to remove one mole of electrons from one mole of a compound to produce one moles of 1+ positive ions all in the gaseous state
Write the first ionisation equation for Magnesium including state symbols
Mg(g) -> Mg+(g) + e-
Write the third ionisation energy equation for argon including state symbols
Ar2+(g) -> Ar3+(g) + e-
What is the three main factors affecting ionisation energy?
Distance from nucleus - smaller atoms have higher attraction between + nucleus and - electrons Nuclear charge - Higher positively charges nucleus means stronger attraction to electrons Shielding between nucleus and outmost electron - Repulsion by electrons in inner shells decreases ionisation energy
Does ionisation energy decrease or increase down a group and why?
IE decreases Bigger atoms, more shielding so weaker attraction from nucleus to outmost electron in outer shells. (Outweighs the increase in protons)
Across a period where is the evidence for sub-levels?
General increase in IE due to increasing protons and no increase in shielding. However there will be spotted drops in IE due to sub shells
How does ionisation energy change across a period?
Increase ionisation energy as the proton number gets larger which makes the atoms smaller. Due to the same level of shielding their is stronger attraction between nucleus and outmost electron
What are sub shells?
A subdivision of electron shells separated by electron orbitals
List the subshells
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6
What does each principle energy level have?
1 - 1s 2 - 2s, 2p 3 - 3s, 3p, 3d 4 - 4s, 4p, 4d, 4f
How many electrons in the principle energy level 3?
18
State Hund’s rule
Electrons prefer to occupy orbitals on their own, and only pair up when no empty orbitals of the same energy are available.
Uses of mass spectrometry
Identify unknown compounds Determine the abundance of each isotope in an element Gain information about structure and chemical properties of molecules
Different stages TOF calculations
Ionisation, acceleration, flight tube, detection, analysis
TOF equation rearranged for mass
2KE / v^2
TOF equation rearranged for v
√(2KE / m)
What is the only constant variable for all samples in TOF?
KE
In electrospray ionisation TOF, what is the last step?
Removing 1 from final answer for H+ initially added
State how ions are detected, and how the abundance of each ion is measured, in a TOF mass spectrometer? [2]
[1] Ions gane an e- [2] Current induced is proportional to abundance
How to calculate Ar of an isotope
Σ(Isotope x abudance) / 100 or total relative abundance
Advantage of electronspray over electron impact
Does not result in fragments in large molecules (Mr)
Why do isotopes have similiar chemical properties? [1]
Same electron configuration
Electronspray ionisation and electron impact standard equations
ESI: M(g) → X+(g) + e- Electron impact: M(g) + H+ → MH+(g)
Conditions of mass spec
Done in vaccum or electrons would collide with moelcules present in air