Atomic Structure

Question 1

Relative atomic mass (Ar)

Answer 1

Average mass of an atom of an element relative to 1/12 the mass of an atom of 12C

Question 2

Ionisation energy

Answer 2

The energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of 1+ ions in the gas state under standard conditions

Question 3

Trend in IE down a group

Answer 3

• increased shielding due to more occupied inner energy levels
• the outermost e- is further from the nucleus
• it is less attracted to the nucleus and requires less energy to be removed

Question 4

Explain the different in ionisation energy between Li and Na

Answer 4

• the electron removed from lithium comes from the 2nd energy level
• e- removed from sodium comes from 3rd energy level
• the outermost e- in Na experiences greater shielding
• the outermost e- is further from the nucleus and is less attracted to the nucleus
• less energy is required to remove an e- from Na

Question 5

Factors that affect the value of IE

Answer 5

• distance between the outermost electron and the nucleus
• nuclear charge / no. Protons
• shielding

Question 6

What is shielding

Answer 6

Repulsion due to inner occupied energy levels

Question 7

Why does IE increase across a period

Answer 7

• the electrons fill the same main energy level
• the outermost e- experiences the same shielding
• distance between nucleus and outermost electron slightly decreases
• the nuclear charge increases, so the outermost electron is more attracted to the nucleus

Question 8

1st energy level

Answer 8

s subshell = 2e-

Question 9

2nd energy level

Answer 9

s subshell = 2e-
p subshell = 6e-

Question 10

3rd energy level

Answer 10

s subshell = 2e-
p subshell = 6e-
d subshell = 10e-

Question 11

4th energy level

Answer 11

s subshell = 2e-
p subshell = 6e-
d subshell = 10e-
f subshell = 14e-

Question 12

What energy level has the greatest energy gap

Answer 12

The 1st and 2nd energy levels

Question 13

What is special about 4s

Answer 13

It fills first and empties first

Question 14

Electron arrangement exceptions

Answer 14

Cr: [Ar]4s1 3d5

-> an e- moves from 4s to 3d for more stability bc a filled or half filled subshell is more stable

Cu: [Ar]4s1 3d10

Question 15

Why is the 1st IE of B less than Be

Answer 15

• the e- removed from B comes from the 2p subshell whereas Be comes from 2s
• the 2p subshell is slightly further from the nucleus
• shielding is the same
• e- from B is less attracted to the nucleus and can be lost easier

Question 16

Why is the 1st IE of O less than N

Answer 16

• the e- removed from O comes from orbital containing 2e-
• the e-e repulsion within the orbital means that less energy is required to remove one of them

Question 17

Successive IE

Answer 17

Energy needed to remove an e- increases with the no. of e- removed because the e- is removed from an increasingly +ve ion so there is more attraction for the remaining e-

Question 18

Why is the 6th IE much larger than the 5th IE

Answer 18

Because the 6th e- is removed from the 2nd energy level, whereas the 5th energy level- comes from the 3rd energy level

-> the 6th e- is closer to the nucleus and experiences less shielding

Question 19

What is electrospray ionisation used for

Answer 19

For substances with a higher molecular mass like proteins
-> prevents fragmentation making it easier to see the peaks

Question 20

Units used in n KE=1/2mv

Answer 20

m
- mass of 1 ion in kg (~10-26kg)
-> ~10-23 g

Question 21

Units in v=d/t

Answer 21

d
- ~1m
- ~10-4s

Question 22

To calculate mass of ions

Answer 22

Mr/1000 to get kg
Then..
Answer/6.022x10^23

Question 23

What is avogadros cosntant

Answer 23

Mass of 1mol

Question 24

Mass spectrometry can be used to..

Answer 24

• find the abundance and mass of each isotope in an element allowing us to determine relative atomic mass
• find the relative molecular mass of a substance made of molecules

Question 25

General stages of mass spec

Answer 25

1. Ionisation - electrospray or electron impact 2. Acceleration 3. Flight tube 4. Detection

Question 26

Electron impact ionisation

Answer 26

- sample is vaporised - high energy electrons fired at sample from a hot wire filament - this knocks of 1 electron frkm each particle forming a 1+ ion - the 1+ ions are attracted towards a -ve plate where they are accelerated

Question 27

What is electron impact used for

Answer 27

- elements and substances with low formula mass - the molecular ion often breaks down into smaller fragments some of which are detected in the mass spectrum X(g) + e- -> X+(g) + 2e-

Question 28

Electrospray ionisation

Answer 28

- sample is dissolved in a volatile solvent and injected through a fine hypodermic needed to give a fine mist - the tip of the needle is attached to a high-voltage power supply - the particles are ionised by gaining a proton from the solvent as they leave the needle forming XH+ ions X(g) + H+ -> XH+ - the solvent evaporates away

Question 29

What is electrospray ionisation used for

Answer 29

Substances with high molecular mass like proteins -> fragmentation rarely takes place

Question 30

Acceleration

Answer 30

The +ve ions are accelerated using an electric field so that they all have the same kinetic energy -> since all particles have the same KE the velocity of each particle depends on its mass Lighter velocity = faster velocity

Question 31

Detection

Answer 31

- the +ve ions hit the negatively charged plate - when they hit the play the ions gain electrons from the play - this generates a movement of electrons and so an electric current

Question 32

The size of the current..

Answer 32

Gives a measure of the number of ions hitting the plate

Question 33

What does a mass spectrum show

Answer 33

The mass to charge ratio and abundance of each ion that reaches the detector -> the m/z is effectively the mass of each ion since each ion has a 1+ charge

Question 34

For molecules ionised by electron impact the signal with the greatest m//z value..

Answer 34

Is from the molecular ion and its m/z value gives the Mr -> however there may be some other small peaks present around the molecular ion peak due to molecular ions that contain different isotopes

Question 35

Isotopes have similar..

Answer 35

chemical properties because they have the same electronic structure

Question 36

Isotopes may have slightly varying..

Answer 36

physical properties because they have different masses

Question 37

Mass spec needs to be in… because…

Answer 37

It needs to be under a vacuum otherwise air particles would ionise and register on the detector

Question 38

The mass spectrometer can be used to..

Answer 38

determine all the isotopes present in a sample of an element and to therefore identify elements

Question 39

If asked to give the species for a peak in a mass spectrum..

Answer 39

Give charge and mass number Eg. 24Mg+