atomic structure Flashcards
relative mass of an electron?
1/1840
what is an isotope?
atoms of the same element with a different number of neutrons but the same proton number
why is the 4s sub-shell filled before the 3d sub-shell?
it has a lower energy
what can the mass spectrometer be used to do?
identify atomic / molecular mass
find relative isotopic abundance
identify elements
name all five parts of a mass spectrometer
vacuum ionisation acceleration ion drift detection
why are the ions kept in a vacuum during mass spectrometry?
prevents ions produced colliding with molecules from the air
what happens during electron impact to ionise atoms?
the sample is vaporised
high energy electrons fired from electron gun
knocks one electron off each particle
forms 1+ ion
equation to show process of electron impact
X(g) + e- —–> X+(g) + 2e-
what is the purpose of acceleration during ToF?
GIVE ALL IONS THE SAME KINETIC ENERGY
positive ions accelerate towards negative plate
(lighter and more highly charged ions = higher speed)
describe ion drift during ToF
ions travel through hole in the negative plate
form a beam
travel down FLIGHT TUBE
what is detection during ToF?
ions with same charge reach detector
lighter ones = first as they have HIGHER VELOCITIES
—–> flight times are recorded
- positive ions pick up e- at detector —— causes current to flow
define the first ionisation energy
energy required to remove one mole of e- from one mole of atoms in the gaseous state
(measured in kjmol-1)
why is the first ionisation energy the lowest?
least energy required
removing electrons from a NEUTRAL atom
general trend in ionisation energies across a period
generally increase as the nuclear charge increases but shielding remains constant
why does the IE decrease between Mg and Al?
Mg = 2p6, 3s2 Al = 2p6, 3s2, 3p1
outer 3p electron in aluminium is in a higher energy level and so is slightly easier to remove
