physical chemistry

what is time of flight mass spectrometry

analytical technique to identify different isotopes

& find overall relative atomic mass of element

steps to TOF

ionisation

acceleration

flight tube

detection

describe ionisation in TOF

happens to elements & low Mr compounds

sample of element is vaporised & injected into mass spectrometer

high voltage passed over chamber

electrons removed from atoms (ionised)

describe acceleration in TOF

positive ions accelerated by electric field

so all ions have same KE

describe flight tube step in TOF

ions set off along flight tube at same time

lighter ions = faster & seperate out

lightest ion reach detector first

ions distinguished by diff flight times

equation for time of flight

distance/particle velocity

describe detection in TOF

positive ions hit negative plate

producing electric current

size of current is directly proportional to number of ions

describe analysis in TOF

current values used in combination with flight times to produce spectra print out

how to find Ar from TOF

Ar= m/z x abundance divide by total abundance

explain the chlorine spectra

chlorine has 2 isotopes 35CL 37CL

have natural abundance ratio 3;1

in mass spec that gives 3;1 peak ratio for CL+ ions

9;61 ratio for CL2+

there’s characteristic pattern

what are the different electron orbitals

S, D , P

How many electrons does S hold

2

how many electrons does p hold

6

how many electrons does d hold

10

how many electrons does f hold

14

what happens to energy as shells increase

energy levels increase

order of electronic configuration

1S

2S

2P

3S

3P

4S

3D

4P

what do electrons pair with in electronic configuration

pair with opposite spin

why do electrons pair with the opposite spin

they repel

so atom is stable

define first ionisation energy

amount of energy required to remove 1 mol of electrons from each atom in a mole of atoms in the gaseous state

eg H(g)——→ H+(g) + e-

define second ionisation energy

amount of energy required to remove 1 mol of electrons from one mol of 1+ ions in the gaseous state to form 1 mol of 2+ ions

eg Ti+ (g)——> Ti2(g)+ + E-

factors that affect ionisation energy

attraction of nucleus

distance between electrons & nucleus

shielding of attraction of nucleus

how does attraction of nucleus affect ionisation energies

more protons in the nucleus means greater attraction

so more energy required

how does distance between electrons & nucleus affect ionisation energy

when atomic radius increase

further outer electrons from nucleus

so weaker arrtaction

so energy decrease

how does shielding of attraction of nucleus affect ionisation energy

electron in outer shell is repel by electrons in complete inner shell

so weakens attraction of nucleus

why is second ionisation energy always more than first

when first electron removed , positive ions form

ion increases attraction on remaining electron

so energy required to remove next is more

how is ionisation energy linked to electronic structure

ionisation energy steadily increase

but when electron being removed is in innermost shell, energy significantly increase

cuz inner shell close to nucleus so attached strongly by nucleus

and no shielding

why do first ionisation energy decrease down group

down group, outer electrons found in shells further from nucleus

so more shielded so attraction of nucleus is smaller

why’s there a general increase in 1st ionisation energy across period

across period, electrons added to same shell

which has same distance from nucleus

& same shielding effect

proton number increase so attraction of nucleus is greater