Atomic structure Flashcards
define what an isotope is
atoms with the same number of protons but different number of neutrons
what are the two types of ionisation?
- electrospray
- electron impact
why does mass spectrometer need to be under a vacuum
this is so that air particles dont ionise and register on the detector
describe electron impact ionisation
a vapourised sample is injected at low pressure and an electron gun fires high energy electrons at the sample this knocks off an electron forming a 1+ ion
equation for electron impact
Ti (g) —— Ti + (g) + e-
describe electrospray ionisation
the sample is dissolved in a volatile solvent and is then injected through a fine hypodermic needle giving a fine mist. the tip of the needle has high voltage at the tip of the needle the sample gains a proton from the solvent forming XH+
what is electron impact typically used for ?
for elements and substances with a low formula mass ( fragmentation)
electron impact can cause larger organic molecules to fragment
whats electrospray ionisation used for?
used for larger organic molecules . the “softer” conditions means fragmentation doesnt occur
Acceleration - what happens?
- positive ions are accelerated by an electric field to a constant velocity.
NOTE: given that all particles have the same kinetic energy the lightest particles will reach the detector first.
Detection ( final step)
the ions reach the detector and generate a small current. the current is produced by electrons transferring from the detector to the positive ions
which is lost first when forming an ion 3d or 4s?
4s
define first ionisation energies
The first ionisation energy is the energy required to remove one mole of electrons from one mole of atoms of an element to form one mole of 1+ ions E.g. the first ionisation energy of gaseous calcium:
Ca (g) → Ca+ (g) + e-
define second ionisation energies
after1st ionisation energy
Second ionisation energy is defined by the equation:
X+(g) X2+(g) + e-
It is the energy required to remove a second electron from each ion in 1 mole of gaseous 1+ ions to give gaseous 2+ ions.
what are the factors that affect ionisation energies
1) nuclear charge ( the more protons in the nucleus the greater the attraction)
2) shielding ( an electron in an outer shell is repelled by electrons in complete inner shells )
3) atomic radius ( the bigger the atom the further the outer electrons are from the nucleus and the weaker the attraction to the nucleus.
why are successive ionisation energies always larger?
this is because when the first electron is removed it forms an positive ion. The ion increases the attraction on the remaining electrons and so the energy required to remove the next electron is larger
why does Helium have the largest ionisation energy?
its first electron is in the first shell closest to the nucleus and has no shielding effects from inner shells. Helium has a bigger first ionisation energies than H as it has one more proton.
why does ionisation energy decrease down a group?
this is because as you go down the group the outer electrons are found in shells further from the nucleus and are more shielded so the attraction of nucleus becomes smaller
why is there a general ionisation energy increase across a period?
as you go across a period the electrons are being added to the same shell which has the same distance from the nucleus and same shielding effect. however the number of protons increases making the attraction of the nucleus greater
why does sodium (Na) have lower ionisation energy than neon?
this js because Na will have its outer electron in the 3s subshell further from the nucleus and is more shielded therefore meaning Na outer electron is easier to remove and has a lower ionisation energy
why is there a small drop from Mg to Al?
this is because Al is starting to fill a 3p subshell whereas Mg has its outer electron in the 3s subshell. electrons in the 3p shubshell are slightly easier to remove because the 3p electrons are higher in energy and are also slightly shielded by the 3s electrons.
why is there a small drop from P to S
this is because in sulfur there are 4 electrons in the 3p subshell meaning that one of the 3p orbital will be fully filled this causes a slight repulsion between the two negatively charged electrons which makes the electron in sulfur easier to remove
define the term orbital
a region around the nucleus which can hold up to two electrons
