P1: Atomic Structure Flashcards
What are protons and neutrons sometimes called, and why?
Nucleons, because they are in the nucleus.
What is relative atomic mass relative to?
Carbon 12, weighing 12
What is 1 mass unit equal to (relative atomic mass)?
1/12 mass of Carbon 12
What is mass (kg) of a proton?
1.673 x 10^(-27)
What is the charge (c) of a proton?
+1.602 x 10^(-19)
What is the mass (kg) of a neutron?
1.675 x 10^(-27)
What is the charge (c) of a neutron?
0
What is the mass (kg) of an electron?
0.911 x 10^(-30)
What is the charge (c) of an electron?
-1.602 x 10^(-19)
What are the Mr’s of a proton, neutron, and an electron?
P: 1
N: 1
E: 1/1840
What do we use Time of Flight Mass Spectrometry for?
To find the abundance mass of each isotope in an element, allowing us to determine its relative atomic mass.
- Can also do molecular
What are the 3 stages of Time of Flight Mass Spectrometry?
- Ionisation- make it a +ion, there are two methods
- Acceleration- Using an electric field so they all have the same kinetic energy
- Flight Tube- Ions travel through a hole in the negative plate, a current is detected and time is taken.
Explain the ‘electron impact’ method for ionisation in ToF
- Sample is vaporised
- An electron gun, hot wire filament, fires high energy electrons at the sample
- This knocks off one electron from each particle, forming 1+ ions
-These are attracted to the negative plate and are accelerated
(fragmentation may occur)
Explain the ‘electrospray ionisation’ method for ToF
- Sample is dissolved in volatile solvent (e.g water) and injected into a fine hypodermic needle
- This creates a fine mist
- The needle is attached to a positive terminal of high voltage power supply
- The particles gain a proton (e.g H+ ion) and are now positive ions
- The solvent evaporates and leaves the + ions to be attracted to the negative plate where they are accelerated.
Why do some ions reach the detector before the other ions? (in ToF)
Lighter ions travel faster as they have more velocity (isotopes) so reach the detector first.
(ToF) What is the kinetic energy formula?
KE= 1/2mv^2
becomes…
KE=1/2m d^2/t^2 when combined with the velocity calc d/t
(ToF) What is the time equation?
t= d⎷m/2KE
or if not given enough values for that, use the KE equation and rearrange
m/t=m/t (t^2)
What are the two ionisation equations? (ToF)
Electrospray:
X(g) + H+ → XH+(g)
Electron impact:
X(g) + e- → X+(g) + 2e-
What are some other names for electron shells?
-Main energy levels
-Orbitals
-Shells
What are the main energy levels labelled as?
1, 2, and 3…
1 being the closest to the nucleus and the lowest energy.
Where are the sub-levels of orbitals found?
Level 1: s
Level 2: s + p
Level 3: s + p + d
also f (not needed)
Explain the ‘ s ‘ sub-unit
- All orbitals have them
- Hold up to 2 electrons, with only one group (so just 2)
- The first two groups of the periodic table.
The diagram is a circle around the origin in a graph.
Explain the ‘p’ sub-unit
- Starts at level 2 and carries on
- Holds 2 electrons in each, with 3 groups (so 6 altogether)
- Begins after the transition metals on the periodic table.
There are 3 diagrams, all have a figure of 8 shape in these directions on the axis ↑ → and diagonal right.
Explain the ‘d’ sub-unit
- Starts at level 3 and so on, however although it belongs to the level 3 group, it comes after 4s as this has lower energy (and follows the periodic table structure)
- Hold 2 electrons each, with 5 groups (so 10 altogether)
- The transition metals on the periodic table.
We don’t need to know the diagrams.
How are the main energy levels arranged with the sub-units (☐) in a diagram?
| | 5p☐☐☐ | 4d☐☐☐☐☐ | 5s☐ | 4p☐☐☐ | 3d☐☐☐☐☐ | 4s☐ | 3p☐☐☐ | 3s☐ | 2p☐☐☐ | 2s☐ | | 1s☐ ^Energy
*notice how the 4s is below the 3d as 4s is lower in energy, even though 3d is technically still level 3
What is a spin?
A property that electrons have within an orbital.
- There is and up spin and a down spin
- Two electrons in the same orbital must have opposite spins
Represented by half arrows (like in an equilibria reaction)
What are the 3 rules of allocating electrons to orbitals?
- Low energy orbitals must be filled first, so the lowest main energy level, with the lowest sub unit (s).
- Orbitals with the same energy levels (e.g p and d) must fill singularly before paired (otherwise repulsion occurs) so 3d: 3 up arrows before any down arrows are added.
- No orbital can have more than two electrons in it, so only two arrows.
How do you write electron shell configurations?
e.g 10 electrons
1s^2 , 2s^2 , 2p^6
1= energy level
s= sub-unit
^x= how many electrons
Define ionisation energy
The energy required to remove an electron from an atom
-From one singular atom, so may need to be in vapour form
Why does the ionisation energy increase as we go down an energy level and each electron?
-Energy level 3 is the furthest away from the nucleus therefore has the least attraction, as you go down levels, the energy required increases
-A slight increase in energy occurs as each electron is taken in one energy level because the ion gets increasingly positive, therefore the attraction is greater.
These are the fist ionisation energies of period 3:
Na- 496
Mg- 738
*Al- 578
Si- 789
P- 1012
*S- 1000
Cl- 1251
Ar- 1521
These should increase as the nuclear charge increases, but why are there anomalies in Al and S?
Al- has an electron in the p sub-unit, slightly higher than the s sub-unit in Mg, therefore further away from the nucleus so less energy needed.
S- has 2 electrons in one p sub-unit (one box) so ‘spin-pair repulsion’ occurs, easier to take away as they are repelling anyway.
Why does the 1st ionisation energy decrease going down group 2?
The number of shells increase, so better atomic shielding and larger atomic radius
Why do we use time of flight mass spectrometry?
Helps work out the mass of an atom
Kinetic energy =?
1/2 m v^2
Velocity=?
distance/ time
Kinetic energy combined with velocity equation?
KE= 1/2 m d^2/t^2
Time with kinetic energy equation?
t= d Square root: m/ 2KE
