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

In TOF what does electron impact mean

an electron is knocked off

In terms of TOF what does electrodpray mean

the Mr+1

in elements what is the oxidation state

always 0

on simple ions what is the oxidation state

charge of the ion

eg cu2+ oxidation state is +2

in a charged compound what must the total of all oxidation states equal

the overall charge of charged compounds

in molecules and more complex ions the more electronegative one is usually ?

negativeb

in neural compounds what must the oxidation state + to?

0

what oxidation state is hydrogen always

+1

what oxidation state is oxygen

-2

what oxidation state is the halogens ?

-1

what oration state is group 1

+1

describe oxidising agents

accepts electrons from species being oxidised

gains electrons & is reduces

reduction in oxidation number

describe reducing agent

donates electrons to species being reduced

loses electrons & is oxidised

increase in oxidation number

how to work out half equations step by step

1. calc oxidation states

2. balance everything except O & H

3. balance O using H20

4. balance H using H+

5. balance the charges using electrons

how to describe the bonding & shapes of molecules

1 state bum of BP & LP

2 stars electron pairs repel & try get as far as possible

3 if no lone pairs , electron pair repel equally

4 if there is LP, Lp repel more than Bp

5 state shape name & bond angle

what happens to the bond angle because lone pairs repel more than bonding pairs?

bond angle is reduced

how to calculate num of outer electrons to find shape of molecule

it’s just number of outer electrons in central atom

how to calculate number of bonding pairs

just the subscript of the other element

how to calculate number of lone pairs

central atom - bp outer electrons

then divide by 2

describe pond polarity in covalent bond

negative charge around covalent bond is not evenly spread

what is electronegativity

power of atom to attract the electrons towards itself within a covalent bond

factors affecting electronegativituy?

atoms size

nuclear charge

electron shielding

effect of electronegativity across period

increases

cuz proton num increases

atomic radius decreases

cuz electrons in same shell pulled in more

effect of electro negativity down group

decreases

cuz distance between nucleus and outer electron increase

so shielding of inner shell electron increase

describe intermediate bonding

continuum of bonding

ionic & cocbalent bonding lie on spec

diff in electronegativity between 2 atom tells where bond lies on the spec