Topic 1 - Atomic Structure Flashcards
What does a mass spectrometer do?
Gives accurate information about relative atomic mass and can be used to identify elements
What conditions does TOF have to be done under?
A high vacuum so new ions don’t collide with molecules in the air.
What is electrospray ionisation?
The sample is dissolved in a volatile and polar solvent.
Then injected through a fine hollow needle connected to a terminal of a high voltage supply which leads the sample (X) to gain a proton and form a positive ion (XH+)
The solvent evaporates into the vacuum and the ions do not.
When do you use electrospray ionisation?
Used for large organic molecules so fragmentation doesn’t occur.
What is electron impact?
Sample is vapourised and injected at low pressure
The electron gun fires high energy electrons at the sample and knocks off an outer electron from the sample causing an ion to be formed.
When is electron impact used for?
Used for elements and substances with low MR.
Not used for larger molecules due to fragmentation.
What happens in acceleration?
The positive ions formed from ionisation are accelerated to a constant KE by a negatively charged plate.
What happens in the flight tube?
The ions spread out and hit the detector at different times, lighter ions reach the detector first as they travel fastest since their velocity is dependent on their mass.
What happens in the detection stage of TOF?
There is a negatively charged detection plate which the positive ions reach and gain an electron which causes a movement of electron which produces a current.
The amount of current produced is proportional to the abundance of the species
What are on the axis of the TOF Mass Spectrometer?
Relative abundance on y
Mass/Charge ratio on x
Define atomic number?
Number of protons in the nucleus of an atom
Define mass number?
Total number of protons and neutrons in the nucleus of an atom
Define isotope?
Atoms of the same element with the same number of protons and different numbers of neutrons
Define first ionisation energy?
The energy needed to remove on mole of electrons from one mole of gaseous atoms of the element to form one mole of gaseous ions with +1 charge each
How has the understanding of atomic structure changed over time?
- John Dalton 19th century - atoms described as solid spheres
- 1897 - electrons discovered and the plum pudding model was theorised - positively charged atom with electrons dotted around
- 1909 - radioactivity discovered - atom now said to be mainly empty space with a nucleus surrounded by a cloud of negatively charged electrons
4) Scientists then proposed the idea of electrons in fixed shells around the nucleus - Bohr model
5) Refined idea to now include sub shells with different energies.
How to determine the relative atomic mass from a mass spectroscopy reading?
Multiply the reading from the y axis (relative abundance) by the x axis reading (mass/charge) this gives you the total mass for each isotope.
Add the different masses together and /100
How to calculate the maximum number of electrons in an electron shell?
Using the equation 2n^2
Where n is the electron shell eg. One closest to the nucleus is 1
What is an atomic orbital?
A region around the nucleus that can hold up to two electrons with opposite spins
Two electrons in an orbital spin in opposite directions
What is a subshell?
All the orbitals of the same type in the same shell
What are the orbitals called?
S
P
D
F
What happens to the energy of the subshells the further away from the nucleus?
Increases
Electron configuration of calcium - 20 electrons
1s2 2s2 2p6 3s2 3p6 4s2
How many electrons can a s,p,d and f orbital hold
s = 2
p = 6
d = 10
f = 14
What fills with electrons first 3d or 4s subshell?
Why?
4s as it has a lower energy level than 3d
