Atomic structure and the periodic table Flashcards
Fundamental particles Mass spectrometry Ionisation energies Electronic configurations Periodicity
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.
mass spectrometry
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
electrospray
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)»_space; X+(g) + e-
electrospray uses
high Mr compounds
electrospray method
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
S orbital
Shape?
Number of electrons?
Where located on periodic table?
Circular orbital made up of 2 electrons.
Sz Sy Sx
P orbitals
Dumbbell shape holding 6 electrons and a variable charge density.
Px Py Pz
D orbital
Double dumbbell shape holding 10 electrons.
Dxy Dxz Dyz Dx(squared)-y(squared) Dz(squared)
Orbital
A region within an atom that can hold up to two electrons with opposite spins.
Aufbau principle
As protons are added to the nucleus, electrons are successively added to orbitals of more energy (starting w lowest) until all electrons are accommodated.
Hund’s rule
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
Emission spectra
Ionisation energies
Emission spectra
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
Ionisation energy
A measure of the energy required to completely remove an electron from an atom of an element.
Trend in successive IE
First electron is easier to remove than 2nd and steady increase for next 8. Final 2 are harder to remove than previous 8.
Final 2 are located in first quantum shell (lowest energy)
Why do successive IEs increase?
As electron lost is at infinite distance to nucleus so energy needs to be increased to a particular value for it to be released. Lower energy= higher IE
Electron electron repulsion
Exists between 2 e- of same/different orbital within a given quantum shell or 2 adjacent quantum shells (most significant).
Impacts on electron energies
Shielding/screening
Nuclear charge
Shielding
Electron electron repulsion between adjacent shells increases energy of electrons and so lowers IE
Charge
Higher charge due to more protons in the nucleus decreases the energy of electrons, increasing IE.
Trends across a period
Nuclear charge increases as atomic number increases (decreasing energy and so increasing IE)
More electrons are added, adding to the electron electron repulsion, increasing e- energy and decreasing IE.
Nuclear charge outweighs effects of shielding,increasing IE across a period.
Successive IE down a group
Nuclear charge increases as protons increase, decreasing electron energy and so increasing IE.
More quantum shells increase shielding and so decrease IE
Shielding overtakes charge impacts, decreasing IE overall
Which groups do the trends in period/group occur in?
2 5 6 7 8
4 is anomaly as Pb has higher than tin
No trend in 3
Periodicity
Regularly repeating pattern of atomic, physical and chemical properties w increasing atomic number.
probability of finding electron within subshell boundary
90% chance
number of orbitals in f subshell
7
therefore 14 electrons
what determines the chemical properties of an element?
the number and arrangement of electrons
what determines physical properties of an element?
the mass of the atom
why do isotopes hold different physical properties to other atoms of the same element?
because it has a different mass
why is RAM not usually a whole number
as is an average of relative isotopic masses (which are usually whole numbers)
what’s relative molecular mass used for?
simple molecules
what’s relative formula mass used for?
ionic or giant covalent compounds
molecular ion
the molecule in which electrons are removed from when bombarded w electrons
molecular ion peak
relative molecular mass of a compound w the highest mass per charge ratio, caused by the molecular ion
S block
group 1 and 2
Cr and Cu electronic configuration
donate one of their 4s electrons to the 3d subshell
4s and 3d subshells difference
4s fill before the 3d
first ionisation energy
energy required to remove one electron from every atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.
what sort of process is ionisation
endothermic
What happens to the melting and boiling points of metals across the period?
increase as metallic bonds grow stronger and radius decreases, meaning higher charge density
