Unit 1A1 Atomic structure Flashcards
what is sub-atomic particle
proton, neutron, electron
what is lower and higher energy level
lowest energy level is the one closest to nucleus
what is relative mass of electron
diff to Alevel ocr A
1/1840
mass in kg of electron
9.109 × 10‐³¹
Mass number is?
number of proton + neutron represented by A
Atomic number is?
Number of proton represented by Z
Definition of isotopes?
atoms with same number of protons but different number of neutrons
Properties of isotopes and why?
Same chemical properties but different physical properties
Because same electrons structure
Because physical properties rely on mass
E.g. of physical properties?
Boiling point
Melting point
Density
Name 5 stages of TOF
Ionisation
Acceleration
Ion Drift
Ion Detection
Data Analysis
What is 2 type of ionisation?
Electron impact
Electrospray ionisation
Describe electron impact?
High energy electrons fired to sample
electron gets knocked off
Atom gets ionised so cataion as lose electron
Describe electrospray ionisation?
High voltage is applied to the sample(dissolved in a solvent)
Each particle is ionised by gaining a proton
Describe acceleration?
Cation are accelerated by electric field to a constant kinetic energy
Rate of acceleration is dependent on mass
If lower mass it travels faster, if higher mass it travels slower velocity
Describe ion drift?
- Ions are allowed to drift in a field-free region
- The time takes for the ions to reach a detector is measured
- ions with a low mass will reach the detector first, and those with a high mass
will arrive last - The mass of the ion can be determined from the time taken
Describe ion detection?
- Positive ions that reach the detector pick up electrons and cause a current to flow in an
ion-current detector - The greater the abundance of the ion, the bigger the current produced
- The detector is linked to an amplifier and then to a recorder, which converts the current
into a peak and that is shown in a mass spectrum - The height of the peak is proportional to the size of the current generated, and
therefore proportional to the abundance of the ion
Describe data analysis?
- Flight times are analysed and recorded as a plot of abundance v mass/charge
(m/z) - Vertical scale sometimes carries no units
-The tallest peak is called the
base peak and sometimes is given the value of 100% for comparison purposes.
-The
higher the peak, the more abundant is the cation.
-So, the y-axis is also sometimes called
relative abundance. Sometimes the y axis is labelled abundance / %.
- The horizontal scale IS NOT JUST MASS but is m/z. What happens when z = 2?
- Molecules can be also ionised
- Or additionally, broken up into simpler particles by a process called fragmentation
What is mass spectra?
graph which shows:
- the m/z for each ion on the x-axis
- the relative abundance for each ion on the y-axis
Mass spectra can be used for?
- identify unknown elements
- calculate Ar values for known elements
- calculate the Mr values for molecular
substances (elements or
compounds)
What is shell？
-Orbits of electron
-Each shell can contain a maximum number of electrons
- This number increases as the shells get further out since the volume available
increases. - Only 2 electrons can fit in the 1st shell but 8 can fit in the 2nd
- Moving out from the centre of the atom the shells are of higher energy.
- So, takes
less energy to escape from the attraction - These shells get closer to each other as they increase in energy
- Also shell can be referred as energy level
-Also each level has principal quantum number, n given
- As n increases the levels get closer until at n = infinity, the
‘edge’ of the atom is reached i.e. the electrons is now free from the nuclear attraction
What is 4 types of sub-level and number of orbitals?
s - 1
p - 3
d - 5
f - 8
What is nature of orbitals?
- e- are constantly moving so finding
exact position is impossible - However, regions where it is more
probable to find an electron is known - This region is called an orbital
- It different shape
- Some referred to as an electron cloud
- Each orbital holds 2 paired electrons and ‘spin’ in opposite directions
What is shape of s and p orbitals?
s - spherical
p - dumb bell, can be x, y or z
Rules for orbital filling?
- Electrons fill the lowest energy levels first.
- Each orbital has a maximum of 2 electrons.
- Two electrons in the same orbital have opposite spin.
- Orbitals of the same energy fill singly before pairing up
Define first ionisation energy?
The energy required to remove one mole of
electrons from one mole of gaseous atoms
3 factors deciding strength of ionisation energy?
- Larger nuclear charge leads to stronger attraction
- Larger radius/higher energy level leads to weaker attraction
- More shielding leads to weaker attraction
What is general trend of ionisation energy in period?
- Ionisation Energy increases across a period
- The number of protons increase
- Shielding is constant / atomic radius decreases
- More energy is required to remove the electron
What is exceptiona for trend of ionisation energy in period?
For group 3:
- Ionisation Energy decreases
- The electron is removed from a higher energy p sub-level
- Less energy is required to remove the electron
For group 6:
- Ionisation Energy decreases
- There is a pair of electrons in a p orbital
- Extra repulsion means less energy is required to remove the electron
Atomic radius trend?
Decrease across period
Increase down group
