1.1- Atomic Structure Flashcards
Details of a neutron?
In the nucleus
Relative mass= 1
Relative charge= 0
Details of a proton?
In the nucleus
Relative mass = 1
Relative Charge = +1
Details of electron?
In orbit around nucleus
Relative mass= 1/1800
Relative charge= -1
Define atomic number?
Number of protons in the nucleus (Z)
Define mass number?
Total number of protons and neutrons in the atom (A)
Number of neutrons?
A-Z
Define isotopes?
Atoms with the same number of protons but different numbers of neutrons
Same chemical properties (same electronic structure)
Varying physical properties (different masses)
Steps in mass spectrometry?
Ionisation- vapourised sample injected at low pressure and an electron gun fires high energy electrons at the sample which knocks out an outer electron forming positive ions with different charges
Acceleration- negative electric field accelerates the positive ions and makes them into a beam
Deflection- The beam of positive ions is deflected by a strong magnetic field. The degree of deflection depends on mass to chard ratio, the smaller this ratio the larger the deflection. By varying the magnetic field ratio, ions of different m/z pass through centre
Detection- the ions reach the detector and generate a small current, which is fed into a computer for analysis
Why do mass spectrometers need to be under a vacuum?
Otherwise air particles would ionise and register on the detector
Formula for relative atomic mass?
R.A.M = sum of (isotopic mass*%abundance)/100
How do you measure the Mr of a molecule using a mass spectrometry reading?
Peak with the largest m/z is equal to the Mr of the molecule
How are electrons arranged?
Principle energy levels (1,2,3..)
Sub energy levels (s,p,d,f)
Orbitals (hold up to two electrons of opposite spin)
How many electrons do each type of sub shell hold?
s- up to 2
p- up to 6
d- up to 10
f- up to 14
How to atoms fill up the sub shells (up to 4p)?
1s 2s 2p 3s 3p 4s 3d 4p
3d is higher in energy than 4s so gets filled after 4s
Define first ionisation energy?
Enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge
H(g) –> H+(g) + e-
Three main factors affecting ionisation energy?
- Attraction to the nucleus (nuclear charge)
- Distance of electrons from the nucleus
- Shielding of attraction of the nucleus
Why is the successive ionisation energies always larger?
When the first election is removed the attraction from the nucleus increases as a positive ion is formed. The ion increases the attraction on the remaining electrons so the energy required to remove the next electron is larger
Define periodicity?
Repeating pattern across a period
Why has He got the largest first ionisation energy?
It’s first electron is in the shell closest to the nucleus and has no shielding effects from inner shells. He has a bigger first IE than H as it has one more proton
Why do first IE decrease down a group?
As one goes down a group, the outer electrons are found in shells further from the nucleus and are more shielded by inner shell electrons so the attraction of the nucleus become smaller
Why is there a general increase in first ionisation energy across a period?
As one goes across a period the electrons are being added to the same shell which has the same distance from the nucleus and same shielding effect. The number of protons increases, however, making the effective attraction of the nucleus greater
Why has Na a much lower first IE than Ne?
Na will have its outer electron in a 3s shell further from the nucleus and is more shielded so the effective attraction from the nucleus is lower.
Why is there a small drop from Mg to Al?
Al is starting to fill a 3p sub shell, whereas Mg has its outer electrons in the 3s sub shell. The electrons in the 3p sub shell are slightly easier to remove and has a lower ionisation energy
Why is there a small drop from P to S?
With sulphur there are 4 electrons in the 3p sub shell and the 4th is starting to doubly fill up the first 3p orbital. When the second electron is added to an orbital there is slight repulsion between the two negatively charged electrons which makes the second electron easier to remove
