Atomic Structure Flashcards
what is mass spectrometry (MS)
instrumental method to find abundance and mass of each isotope in an element, to determine RAM
4 stages in mass spectrometry
ionisation area
acceleration area
ion drift area
detection area
what are the two types of ionization
electron impact ionisation
electrospray ionisation
what happens during electron impact ionisation?
- sample is vaporized
- high speed electrons fired at it form an electron gun
- electron is knocked off
- positive ions are attracted to a negative electric plate where they are accelerated
what can occur during electron impact ionisation?
fragmentation
what happens during electrospray ionization?
-sample dissolved in a volatile solvent
- injected through a hypodermic needle to give a mist
- tip of needle attached to a positive terminal of high voltage power supply
-particles gain a proton from solvent producing H+ ions
-solvent evaporate, H+ attracted to the negative plate where they are accelerated
what happens during acceleration?
- ions are attracted towards a negatively charged plate
- accelerates towards it
- lighter ions and more charged ions achieve a higher speed
what happens during stage 2 acceleration?
positive ions are accelerated so they all gain kinetic energy
what happens during drifting?
ions pass through a hole in the negatively charged plate, forming a beam & travel along the flight tube to a detector
what happens during stage 4 detection:
- positive ions gains an electron when they hit the negatively charged plate
- this creates a current
- size of the current shows the abundance of the ions (number of them hitting the plate)
what reading do you need to read on the electron impact ionization graph?
penultimate peak
(fragmentation can occur)
what reading do you need to read on the electrospray ionization graph? how do we find the Mr from this?
penultimate peak
we must find the subtract 1 to find the Mr as a hydrogen is picked up
equation for relative atomic mass
(abundance x mass) + (abundance x mass) / total abundance
equation for two isotopes of an element
m(1) / t2(1) = m(2) / t2(2)
how to find the mass of an ion
- mass (mass number) / Avogadro constant (6.02 x 10 23)
- divide it by 1000 (to go from grams into kilograms)
how do electrons fill energy levels?
starting with the lowest energy level, which is closest to the nucleus
how can energy levels be split
sub-shells
orbitals
what is an orbital
region of 3d space that has high electron probability density. an orbital can hold a maximum of two electrons
1st energy level
maximum number of electrons it can hold?
how many orbitals?
2 electrons
1s orbital
2nd energy level
maximum number of electrons it can hold?
how many orbitals?
8 electrons
2s orbital and 3 2p orbitals
3rd energy level
maximum number of electrons it can hold?
how many orbitals?
18 electrons
3s, three 3p, five 3d orbitals
4th energy level
maximum number of electrons it can hold?
how many orbitals?
32 electrons
4s, three 4p, five 4d, seven 4f orbital
what fills up first 4s or 3d
4s always
Why are orbitals half filled first?
To reduce repulsion between electrons
What is isoelectronic
Same electron configuration
What is removed for positive ions
We remove the 4s before the 3d
What is the first ionisation energy?
Energy required to form 1 mole of gaseous 1+ ions from 1 mole of gaseous atoms by removing an electron
E.g. Na (g) -> Na+ (g) + e-
What is the second ionisation energy
Energy required to form 1 mole of gaseous 2+ ions from 1 mole of gaseous 1+ ion by removing an electron
Trend in ionisation energy
Down a group
As you go down the group first ionisation energy decrease ( easier to remove an electron)
Why does the ionisation energy decrease down a group
Because
- larger atomic radius
- more shielding from inner shells
(weaker electrostatic attraction between electron & nucleus)
- greater nucleus charge (more protons)
What happens with the ionisation energy across a period and why?
Generally it increases. This is because:
- greater nuclear charge
- atomic radius decreases
- similar electron shielding
what groups are there a change in pattern in ionization energy across a group
between
2-3
5-6
why is there a change in pattern between group 2-3 in ionization energy across a group
the 3p orbital is higher in energy than the 3s orbital. therefore less energy is needed to remove an electron from 3p
why is there a change in pattern between group 5-6 in ionization energy across a group
there is an electron pair repelling in the p orbital; therefore less energy required to remove an electron
Exceptions in electron configuration
Chromium
1s2 2s2 2p6 3s2 3p6 4s1 3d5
Exception in electron configuration
Copper
1s2 2s2 2p6 3s2 3p6 4s1 3d10
