Atomic structure

Question 1

What is meant by relative atomic mass?

Answer 1

The mean mass of an atom compared to 1/12th of the mass of a carbon-12 atom

Question 2

How do you work out the relative atomic mass of an element?

Answer 2

(mass no. x abundance)+(that for other isotopes)/total abundance

Question 3

What are the 4 stages of time of flight mass spectrometry?

Answer 3

1= Ionisation.
2= Acceleration.
3= Flight tube.
4= Detection.

Question 4

Describe electron impact.

Answer 4

1. The sample is vaporised.
2. High energy electrons are fired at it from an electron gun(a hot wire filament with a current running through it that emits electrons).
3. This knocks off one electron from each particle forming a 1+ ion.
   e. g. X(g) -> X+(g) + e-

Question 5

Describe electrospray ionisation.

Answer 5

1. The sample is dissolved in a volatile solvent.
2. The sample is injected through a fine hypodermic needle giving a fine mist.
3. The tip of the needle has high voltage.
4. Each particle gains a proton as it leaves the needle producing XH+ ions.
   e. g. X(g) + H+ -> XH+(g)

Question 6

Describe the acceleration stage of time of flight mass spectrometry.

Answer 6

The positive ions are accelerated using a negative electric plate so that they all have the same kinetic energy.

Question 7

Give the kinetic energy equation.

Answer 7

KE=1/2mv^2 (J, Kg, m/s)

Question 8

Describe the flight tube stage of time of flight mass spectrometry.

Answer 8

Ions travel through the tube at different speeds and take different times to reach the detector.
Lighter particles move faster and so have a shorter time of flight.

Question 9

Describe the detection stage of time of flight mass spectrometry.

Answer 9

1. Positive ions hit a negatively charged plate
2. These positive ions are discharged by gaining electrons from the plate
3. This generates an electric current (movement of electrons) that is measured.
4. The size of current is proportional to the number of ions hitting the plate.

Question 10

Give the equation for time using just distance and velocity.

Answer 10

t=d/v

Question 11

Give the equation for time using distance, mass and kinetic energy.

Answer 11

t=d x √m/2KE

Question 12

How do you know the relative molecular mass of a molecule (after the mass spectrum has been produced by electron impact ionisation)?

Answer 12

1. Look at the group to the right
2. Highest m/z HERE
   I
   I I
   I I I
   I I I I I
   I I I I I I I I
   I__I_I__I_I_____I__I__I__I__I_____

Question 13

For relative molecular mass and via electron impact what causes the peaks below and around the rmm?

Answer 13

Below= Fragmentation of molecular ions.
Around= Molecular ions that contain different ions.

Question 14

How do you know the relative molecular mass of a molecule (after the mass spectrum has been produced by electrospray ionisation)?

Answer 14

1. The one with the biggest peak.
2. Subtract one HERE (X)
   Answer= X-1
   I
   I I
   I I
   I I
   I I
   I________________I____I_____

Question 15

For relative molecular mass and via electrospray ionisation what causes the other peak?

Answer 15

Due to ions containing an atom (isotope) with a higher mass.

Question 16

How do you find the mass of one ion?

Answer 16

X =(g in one mole)
/1000 =(kg in one mole)
/(6.02 x 10^23) =(kg in one ion)

Question 17

What does the first number represent in terms of electron configuration?

Answer 17

Which no. shell.

Question 18

What the letter represent in terms of electron configuration?

Answer 18

The type of subshell/orbital.

Question 19

What does the power represent in electron configuration?

Answer 19

Number of electrons in the subshell

Question 20

How many electrons can the s, p, d & f subshells hold?

Answer 20

s=2
p=6
d=10
f=14

Question 21

What is the full electron configuration all way to a full 4p subshell?

Answer 21

1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6

Question 22

For the electron configurations of the transition metals, which subshell gets filled first 3d or 4s and why?

Answer 22

4s

As it has a lower energy level than 3d.

Question 23

For the electron configuration of an ion would the 3d or 4s lose an electron/s first?

Answer 23

4s

Loses electrons first.

Question 24

What are the electron configurations for the exceptions of Cr and Cu? And why are they like this?

Answer 24

Cr= [Ar] 4s^1 3d^5
not 4s^2 3d^4

Cu=[Ar] 4s^1 3d^10
not 4s^2 3d^9

As it is a slightly lower energy arrangement

Question 25

What does the Aufbau principle state?

Answer 25

That the lowest energy sub-levels are occupies first

e.g. 1s then 2s then 2p etc.

Question 26

What does the Pauli exclusion principle and spin state?

Answer 26

That each orbital may contain no more than two electrons.

Two electrons in the same orbital must have opposite spin.

Question 27

What does Hund’s rule of maximum multiplicity state?

Answer 27

That electrons occupy all empty orbitals within a sub-level before they start to form pairs in orbitals.

Question 28

What does the ionisation energy of an element typically depend on?

Answer 28

1. Atomic radius (distance)
2. No. of protons (Force of attraction)
3. Sheilding/shells

+energy level outer e- is on
(higher energy level=lower IE)
+e- pair (if 1st)
=more e- repulsion= easier to remove

Question 29

Explain the term first ionisation of an atoom.

Answer 29

Enthalpy change when an electron is removed from a gaseous atom.

Question 30

Describe the down a group ionisation energy trend.

Answer 30

As you go down a group the ionisation energy decreases.

Question 31

Explain the down a group trend.

Answer 31

As you go down a group, there is more distance and shielding between the nucleus and the outer electrons meaning that there is less force of attraction so the outer electrons are easier to remove so the ionisation energy required is lower.

Question 32

Describe the across a period ionisation energy trend.

Answer 32

As you go across the period the ionisation energy increases.

Except for the 3rd element and the 6th element.

Question 33

Explain the across a period ionisation energy trend.

Answer 33

As you go across a period the no. of protons increases with the same amount shielding meaning it has a stronger force of attraction and is therefore the outer electrons are closer to the nucleus so electrons are harder to remove so has a higher ionisation energy.

Question 34

Explain the exceptions of the 3rd and 6th element for the across a period trend.

Answer 34

3rd= From an s to a p subshell, p has a higher energy level and so is further away from the nucleus, easier toremove, lower ionisation energy.

6th= 1st electron pair so they repell eachother (more electron pair repulsion), easier to remove, lower ionisation energy.

Question 35

Describe the general trend for successive ionisation energies and explain.

Answer 35

They increase as more electrons are removed.

Once electron removed= more positive= harder to remove= higher ionisation energy.

Question 36

Explain the reason for large increases in successive ionisation energies.

Answer 36

There is a change in shell
= much closer to nucleus
= much harder to remove
= higher ionisation energy

Question 37

What does the group no. represent in terms of successive ionisation energies?

Answer 37

The group= how many electron removals before its a new shell (before the big jump in ionisation energies).