Flashcards in Atomic structure and the periodic table Deck (55)
RELATIVE ATOMIC MASS
The weighted mean mass of an element, compared to 1/12th the mass of an atom of carbon 12.
RELATIVE ISOTOPIC MASS
the mass of an atom of an isotope of the element compared to 1/12th the mass of C12.
Allows calculation of exact relative masses of isotopes from a mass spectrum of element and percentage abundances.
How's the relative molecular mass of a covalent compound obtained from a mass spectrum?
The highest value of mass to charge (m/z) (molecular ion peak) is identified as a peak and therefore corresponds with the relative molecular mass of the covalent compound.
2 forms of spectrometry?
electron impact spectrometry uses?
elements and low Mr compounds
electron impact method
high energy electrons are fired at the sample from an electron gun to knock off electrons and form ions.
equation for electron impact ionisation
X(g) >> X+(g) + e-
high Mr compounds
The sample is dissolved in a volatile solvent and injected via a fine hypodermic needle as a spray into a vacuum of an ionisation chamber with a high voltage at the end of the needle which has a positive charge.
what occurs after ionisation in spectrometry?
ion acceleration via an electric field so all ions have the same kinetic energy
what occurs after ion acceleration in spectrometry?
the charged ions are separated. Drifting as they enter the flight tube, those of different masses will have different flight times.
How are the ions detected in spectrometry?
a negative detector plate produces a current when ions hit them, in which more ions create a larger current. time of flight and the current produced allows determination of relative abundance and mass per charge.
why is ionisation necessary in spectrometry?
so that the ions may be accelerated within the electrical field and allowing detection of mass per charge when the ions produce a current on the negative detector plate.
How are ions accelerated, detected and have their abundance determined in a TOF mass spectrometer?
The ions are accelerated within a vacuum vua the presence of an electric field, causing the ions to drift down the flight tube, attracted to the detector plate which produces a current when electrons are absorbed. The time of flighta nd mass per charge can enable the calculation of abundance and mass.
what's on the x and y axis of a mass spectrum?
x is m/z (mass to charge)
y is relative abundance of ions (%)
equation for flight time of ions in chamber
t=d(square root of
Number of subshells within each quantum shell
1 (one subshell) 1s 2
2 (two subshells) 2s, 2p 8
3 (three subshells) 3s, 3p, 3d 18
4 (4 subshells) 4s, 4p, 4d, 4f 32
Number of electrons?
Where located on periodic table?
Circular orbital made up of 2 electrons.
Sz Sy Sx
Dumbbell shape holding 6 electrons and a variable charge density.
Px Py Pz
Double dumbbell shape holding 10 electrons.
Dxy Dxz Dyz Dx(squared)-y(squared) Dz(squared)
A region within an atom that can hold up to two electrons with opposite spins.
As protons are added to the nucleus, electrons are successively added to orbitals of more energy (starting w lowest) until all electrons are accommodated.
Electrons occupy orbitals singly before pairing takes place.
Pauli exclusión principle
No 2 electrons can occupy the same space unless they have opposite spins.
Why is there exceptions to the aufbau principle?
Electrón-electron repulsión and number of protons in the nucleus.
Evidence for quantum shells
Gaseous atoms given energy via heating/electricity to push electrons to higher energy levels, upon return, EM radiation is emitted.
Analysis of radiation via a spectroscope provides an emission spectra.
Specific frequencies show quantised energies of electrons
A measure of the energy required to completely remove an electron from an atom of an element.