2.8 - Instrumental analysis Flashcards
Where is A and Z on an element?
Z = atomic number
A = mass number
Why is the mass number on a periodic table a decimal?
Decimal number due to mass of isotopes
What is the definition of an isotope?
Atoms of the same element with different numbers of neutrons and different masses
How does the reactivity of isotopes vary?
They react in the same way because they have the same electronic configuration
What is the abundance?
Tells us how common each isotope is.
How does a mass spectrometer work?
- element with all its isotopes placed in a sample chamber
- ionsation converts all atoms into positive ions
- positive ions are attracted to the neegatively charged plates, causing acceleration and increase in KE (ions with same charge have same KE)
- ions pass plate and stop accelerating, drifts towards the detector (ions drift at different velocities light - fast, heavy - slow)
- ions reach detector and gains electrons to make it neutral, causes a current flow, the time taken is used to determine mass and size of current produced is used to determine abundance
Why is mass spectrometry done within a vacuum?
To stop the ions colliding with elements in the air
What does a mass spectrum look like?
Relative aundance (%) on y axis
M/Z ratio or relative mass on x axis
What is the definition of relative isotopic mass?
Mass of an atom of an isotope compared with 1/12th the mass of carbon 12.
What are the 3 rules of relative isotopic mass?
- RIM has no unis
- RIM is a whole number
- 1 RIM per isotope of an element
What is the definition of relative atomic mass?
Weighted mean mass of an atom of an element compared with 1/12th the mass of carbon-12
What is the formula for relative atomic mass through mass spectroscopy?
Ar = (RIM of isotope 1 x abundance)+(RIM of isotope 2 x abundance)/100
What is infrared spectroscopy?
Identifying the bonds in a molecule due to them absorbing different frequencies of infrared.
Used to identify functional groups
What does a infrared spectroscopy look like?
Transmittance / wavenumber
Uses trophs to shows bonds present in a molecule
What is the fingerprint region?
Area thats really messy between 500-1000, specific to the molecule
What is nuclear magnetic resonance spectroscopy?
- using absorption of different frequency radiowaves to indentify different parts of a molecule
- similiar to IFS, but this is about the nucleons in a atom
How does NMR work?
- protons and neutrons have spins too
- if a magnetic field is applied, their spins line up along or against it
- if no. of nucleons is even, they are balanced
- if no. of nucleons is odd, radio waves can be absorbed so that the spin can be flipped
- nucleons in different environments can absorb different frequencies
What is NMR measured relative to?
Standard substance Si(CH3)4 or TMS for short
Used because it is unreactive and volatile, and only asorbs one frequency because its 1 environment
What does 13C NMR do?
give the proportion of different carbon bonds in a sample
What affects chemical shifts?
The distance from functional groups, can effect the number of peaks due to different environments (can be detected through symmetry)
What is H NMR?
- aka proton NMR
- can give proportions of H in different environments
- use of ratios
What do high resolution NMR’s show?
Peaks split due to neighboring carbons
no of splits = no, H’s on neighbouring atom + one
What is the difference between a 13C NMR and 1H NMR?
13C NMR - gives you what carbons are bonded to
1H NMR - what hydrogens are bonded to, how many hydrogens in the same environment, how many hydrogens on neighbouring carbons (split peaks)
