atomic structure notes Flashcards
what evidence was found to support Rutherford’s model?
majority of the helium nuclei passed through
most of the atom must be empty space
very small number of ions were deflected and reflected because nucleus is positive and dense
ionisation energy
the energy required to removed one mole of electrons from one mole or gaseous atoms
Three key factors that Will influence lonisation Energy
Nuclear Charge (the number of protons in the nucleus)
Distance from the nucleus
Shielding
The following data shows the first seven successive ionisation energies of a period 3 element. State which element it is and explain your reasoning.
• The biggest jump is between the 4th and 5th ionisation energies
• the 5th electron is on the shell closer to the nucleus
• The element must have 4 electrons on its outer shell
• in period 3 this must be Silicon.
Why is Li a bigger atom than Be?
same shielding
Be has more protons
so attracts outer electron more strongly
Why is Li a bigger atom than He?
Li has more protons
Li has more shielding
Li has a bigger atomic radius
the outer electron is less strongly attracted to the nucleus
Why is Li a bigger atom than F?
same shielding
F has more protons
more strongly attracts outermost electron
Why is Li+ a smaller ion than F-?
F- has more shielding
the outermost electron is less strongly attracted to nucleus
The 1stIE will increase
more protons
shielding stays the same
Within the s sub-shell there is…
one S orbital
Within the p sub-shell there are…
3 P orbitals
Within the d sub-shell there are
5 D orbitals
Exceptions for electron configurations of d-block atoms and ions:
Exception 1 - Chromium
1S2 2S2 2p6 3s2 3p6 4s1 3d5
Exception 2 - Copper
1s2 2s2 2p6 3s2 3p6 4s1 3d10
How does the ionisation energy change down a group?
atom gets bigger
more shielding
weaker attraction between outermost electron and nucleus
ie decreases down group
Q: Why does the atomic radius gets smaller from right to left across a period?
number of protons increases
greater attraction between outermost electron and nucleus
shielding stays same
the mass spectrometer measure two factors:
relative abundance
mass to charge ratio
why is mass spectrometry in a vacuum?
to prevent any of the particles being
tested colliding with molecules from the air.
a: Why are the sample particles ionised?
So they can be accelerated towards the negatively charged plate
So they generate a current when they hit the detector
How is the ion accelerated?
Positive ions attracted to the negatively charged plate
All ions have the same kinetic energy
How are ions separated in the flight tube?
lons travelling at higher speeds (small m/z) move ahead of those travelling more
slowly (large m/z)
How are the ions detected?
Each ions hits the detector
Ion gains an electron
Generates a current
Size of the current is proportional to the abundance of the ion
Electron impact
sample being analysed is vaporised and then high energy electrons are fired at it
the high energy electrons come from an “electron gun’ which is a hot wire filament with a
current running through it that emits electrons.
This usually knocks off one electron from each particle forming a 1*ion.
Calculating Ar
This is often used to calculate the relative atomic mass (A) of elements.
Key Formulae:
Ar= (Mass 1 x Abundance 1) + (Mass 2 x Abundance 2) + (Mass n x Abundance)
————————————
sun of Abundances
KE=
KE = ½ mv2
KE rearranged for M
m = KE
——-
1/2V2
KE reg arranged for V2
V2= KE
————-
1/2M
