Atomic structure Flashcards
isotopes definition
atoms with the same amount of protons but a different number of neutrons
why do isotopes exist?
there can be different numbers of neutrons in the nucleus of atoms of each element
what is the mass spectrometer used for
to identify elements and their relative molecular mass
relative isotopic mass
relative abundance of isotopes
why is the mass spectrometer apparatus in a vacuum
to prevent ions colliding with air particles
what are the 4 steps of mass spectrometry
1) ionisation
2) acceleration
3) ion drift through flight tube
4) ion detection
names of the different methods of ionisation
electron impact and electrospray
describe electron impact
sample is vaporised
electron gun fires high energy electrons at it
one electron from each particle is knocked off
forms a 1+ ion
electron impact equation
X(g) + e- –> X+(g) + 2e-
which elements/ substances is electron impact for and why
with low formula mass
molecular ion may break down into fragments
describe electrospray
sample is dissolved in a volatile solvent and is injected through a hypodermic needle
positive terminal of a high voltage power supply is attached to the tip of the needle
particles gain a proton from the solvent
solvent evaporates away
leaves 1+ ions to accelerate towards the negative plate
electrospray equation
X(g) + H+ –> XH+(g)
which elements/ substances is electrospray used for
with higher molecular mass
describe the acceleration process
positive ions are accelerated by an electric field
all have equal KE
ions with different masses have different velocities
lighter ions have higher velocities
describe ion drift through flight tube process
positive ions travel through a hole in the negatively charged plate into a flight tube
ions with different masses seperate
time of flight of each ion depends on its mass
describe ion detection process
positive ions hit a negatively charged electric plate
ions become discharged by gaining electrons
this movement of electrons generates an electric current which is measured
current is related to abundance
why does the sample need to be ionised for mass spectrometry
for acceleration and detection
what does the mass spectrum show
shows the mass tp charge ratio and abundance of each ion that reaches the detector
relative atomic mass equation
= combined mass of all isotopes/ combined abundance of all isotopes
first ionisation energy definition
the enthalpy change when an electron is removed from each atom in a mole of gaseous atoms to form one mole of 1+ gaseous ions
equation for first ionisation energy
X(g) –> X+(g) + e-
equation for n ionisation energy
X^(n-1)+(g) –> X^n+(g) + e-
rule for which electron removed
highest energy electrons are lost first when an ion is formed
are ionisation energy reactions endo or exothermic
endothermic
energy required to remove an electron by overcoming the forces of attraction between the e- and positive nucleus
factors affecting ionisation energy (3)
distance between highest energy electron and nucleus
nuclear charge
shielding (repulsion) by electrons in inner shell between nucleus and outer shell electron
trend of 1st ionisation energy down a group
requires less energy down a group
- more shielding as more energy levels
- further distance from nucleus
general trend of 1st ionisation energy across a period
generally requires more energy
- increase in nuclear charge
- atoms become smaller so closer distance
why is there a decrease in 1st ionisation energies from group 2-3
p orbital is higher in energy than s orbital
why is there a decrease in 1st ionisation energies from group 5-6
extra electron-electron repulsion within orbital makes it easier to lose electron
general trend for successive ionisation energies of an element
generally requires more energy for the next electron lost
- highest energy electrons become closer to the nucleus
- less shielding
- ions increases attraction with other electrons
why are there some bigger jumps between some successive ionisation energies
more energy is required to remove electrons at the next energy level which is lower in energy
- less shielding
- increase ion charge
- closer distance
rules for filling up energy levels
hunds rule
aufbau principle
paulis principle
4s is filled and emptied before 3d
Cr and Cu loses one electron from 4s to 3d
shorthand uses previous noble gas + additional electrons
hund’s rule
electrons prefer to occupy orbital on their own (parallel spin) and only pair up (opposite spin) when no empty orbitals of the same energy level are available
aufbau principle
electrons fill up lowest (sub)energy levels first
pauli’s principle
each orbital holds a maximum of 2 electrons
