3.1.1 atomic structure + mass spec Flashcards
describe John Dalton’s theory of the atom
1800s - BILLARD BALL
believed atoms where solid spheres
different elements made from diff types of spheres
describe J.J Thomson’s theory of the atom
1897 - PLUM PUDDING MODEL
believed that atoms must contain a negative charge
deduced the atom is a cloud of +ive charge (pudding) w/ -tively charged particles inside
explain Ernest Rutherford’s experiments and theory of the atom
1909-1911
fired alpha particles at the thin gold sheet
expected them to be diffracted
most of them passed through with few diffracted
concluded atom must have +ive nucleus with -ive cloud around it and it’s mostly empty space
explain Niels Bohr’s theory of the atom
Rutherford model had a flaw - nothing stopping -ive cloud from spiralling into nucleus
concluded electrons must be in shells and sub shells
had to have fixed E levels
when they moved E levels they gained/lost EM radiation
EM radiation is at a fixed frequency
describe today’s currents atomic model
has a central nucleus w/ neutrons and protons
electrons orbit the nucleus in shells/orbitals
each shell must be filled before next one is used
how do you calculate Ar?
Ar = average mass of isotopes of element/total abundance
how does electron impact ionisation work?
electron gun fires electrons at a sample at high energy
knocks an electron off the sample
creates +ive ion
(for low Mr compounds)
what is the main disadvantage of electron impact?
can cause fragmentation of larger molecules
how does electrospray ionisation work?
sample dissovled in a POLAR VOLATILE solvent
injected into a needle at high voltage
causes sample to gain H+ ion from solvent
(for high Mr compounds)
what are the equations of electron impact + electrospray ionisation?
electron impact:
Na (g)»_space; e- + Na+ (g)
electrospray:
Fe (g) + H+»_space; FeH+ (g)
how are the ions accelerated?
+ive ions are attracted ot the -ively charged detection plate
all ions gain SAME KINETIC ENERGY
lighter ions = greater acceleration
how are the ions detected and abundance determined in a TOF mass spec?
at the detection plate they gain an electron + discharge
causes a current to be produced
SIZE OF CURRENT DIRECTLY PROP TO ABUNDANCE
lighter ions reach first
what is the kinetic energy equation?
KE = 1/2 mv2
why must TOF mass spec occur in a vacuum?
to prevent electrons from colliding with air particles
what is the molecular ion?
the final peak on the mass spec graph
M+
it gives the Ar of the sample used ( since charge is +1 in m/z ratio)
caused by electron impact (fragmentation)
