P1: Atomic Structure

Question 1

What are protons and neutrons sometimes called, and why?

Answer 1

Nucleons, because they are in the nucleus.

Question 2

What is relative atomic mass relative to?

Answer 2

Carbon 12, weighing 12

Question 3

What is 1 mass unit equal to (relative atomic mass)?

Answer 3

1/12 mass of Carbon 12

Question 4

What is mass (kg) of a proton?

Answer 4

1.673 x 10^(-27)

Question 5

What is the charge (c) of a proton?

Answer 5

+1.602 x 10^(-19)

Question 6

What is the mass (kg) of a neutron?

Answer 6

1.675 x 10^(-27)

Question 7

What is the charge (c) of a neutron?

Answer 7

0

Question 8

What is the mass (kg) of an electron?

Answer 8

0.911 x 10^(-30)

Question 9

What is the charge (c) of an electron?

Answer 9

-1.602 x 10^(-19)

Question 10

What are the Mr’s of a proton, neutron, and an electron?

Answer 10

P: 1
N: 1
E: 1/1840

Question 11

What do we use Time of Flight Mass Spectrometry for?

Answer 11

To find the abundance mass of each isotope in an element, allowing us to determine its relative atomic mass.
- Can also do molecular

Question 12

What are the 3 stages of Time of Flight Mass Spectrometry?

Answer 12

1. Ionisation- make it a +ion, there are two methods
2. Acceleration- Using an electric field so they all have the same kinetic energy
3. Flight Tube- Ions travel through a hole in the negative plate, a current is detected and time is taken.

Question 13

Explain the ‘electron impact’ method for ionisation in ToF

Answer 13

• Sample is vaporised
• An electron gun, hot wire filament, fires high energy electrons at the sample
• This knocks off one electron from each particle, forming 1+ ions
  -These are attracted to the negative plate and are accelerated

(fragmentation may occur)

Question 14

Explain the ‘electrospray ionisation’ method for ToF

Answer 14

• Sample is dissolved in volatile solvent (e.g water) and injected into a fine hypodermic needle
• This creates a fine mist
• The needle is attached to a positive terminal of high voltage power supply
• The particles gain a proton (e.g H+ ion) and are now positive ions
• The solvent evaporates and leaves the + ions to be attracted to the negative plate where they are accelerated.

Question 15

Why do some ions reach the detector before the other ions? (in ToF)

Answer 15

Lighter ions travel faster as they have more velocity (isotopes) so reach the detector first.

Question 16

(ToF) What is the kinetic energy formula?

Answer 16

KE= 1/2mv^2

becomes…

KE=1/2m d^2/t^2 when combined with the velocity calc d/t

Question 17

(ToF) What is the time equation?

Answer 17

t= d⎷m/2KE

or if not given enough values for that, use the KE equation and rearrange

m/t=m/t (t^2)

Question 18

What are the two ionisation equations? (ToF)

Answer 18

Electrospray:

X(g) + H+ → XH+(g)

Electron impact:

X(g) + e- → X+(g) + 2e-

Question 19

What are some other names for electron shells?

Answer 19

-Main energy levels
-Orbitals
-Shells

Question 20

What are the main energy levels labelled as?

Answer 20

1, 2, and 3…

1 being the closest to the nucleus and the lowest energy.

Question 21

Where are the sub-levels of orbitals found?

Answer 21

Level 1: s
Level 2: s + p
Level 3: s + p + d

also f (not needed)

Question 22

Explain the ‘ s ‘ sub-unit

Answer 22

• All orbitals have them
• Hold up to 2 electrons, with only one group (so just 2)
• The first two groups of the periodic table.

The diagram is a circle around the origin in a graph.

Question 23

Explain the ‘p’ sub-unit

Answer 23

• Starts at level 2 and carries on
• Holds 2 electrons in each, with 3 groups (so 6 altogether)
• Begins after the transition metals on the periodic table.

There are 3 diagrams, all have a figure of 8 shape in these directions on the axis ↑ → and diagonal right.

Question 24

Explain the ‘d’ sub-unit

Answer 24

• Starts at level 3 and so on, however although it belongs to the level 3 group, it comes after 4s as this has lower energy (and follows the periodic table structure)
• Hold 2 electrons each, with 5 groups (so 10 altogether)
• The transition metals on the periodic table.

We don’t need to know the diagrams.

Question 25

How are the main energy levels arranged with the sub-units (☐) in a diagram?

Answer 25

  |
  |          5p☐☐☐
  |                         4d☐☐☐☐☐
  | 5s☐
  |          4p☐☐☐
  |                         3d☐☐☐☐☐
  | 4s☐
  |          3p☐☐☐
  | 3s☐
  |          2p☐☐☐
  | 2s☐
  |
  | 1s☐ ^Energy

*notice how the 4s is below the 3d as 4s is lower in energy, even though 3d is technically still level 3

Question 26

What is a spin?

Answer 26

A property that electrons have within an orbital.
- There is and up spin and a down spin
- Two electrons in the same orbital must have opposite spins

Represented by half arrows (like in an equilibria reaction)

Question 27

What are the 3 rules of allocating electrons to orbitals?

Answer 27

1. Low energy orbitals must be filled first, so the lowest main energy level, with the lowest sub unit (s).
2. Orbitals with the same energy levels (e.g p and d) must fill singularly before paired (otherwise repulsion occurs) so 3d: 3 up arrows before any down arrows are added.
3. No orbital can have more than two electrons in it, so only two arrows.

Question 28

How do you write electron shell configurations?

Answer 28

e.g 10 electrons
1s^2 , 2s^2 , 2p^6

1= energy level
s= sub-unit
^x= how many electrons

Question 29

Define ionisation energy

Answer 29

The energy required to remove an electron from an atom

-From one singular atom, so may need to be in vapour form

Question 30

Why does the ionisation energy increase as we go down an energy level and each electron?

Answer 30

-Energy level 3 is the furthest away from the nucleus therefore has the least attraction, as you go down levels, the energy required increases
-A slight increase in energy occurs as each electron is taken in one energy level because the ion gets increasingly positive, therefore the attraction is greater.

Question 31

These are the fist ionisation energies of period 3:
Na- 496
Mg- 738
*Al- 578
Si- 789
P- 1012
*S- 1000
Cl- 1251
Ar- 1521

These should increase as the nuclear charge increases, but why are there anomalies in Al and S?

Answer 31

Al- has an electron in the p sub-unit, slightly higher than the s sub-unit in Mg, therefore further away from the nucleus so less energy needed.

S- has 2 electrons in one p sub-unit (one box) so ‘spin-pair repulsion’ occurs, easier to take away as they are repelling anyway.

Question 32

Why does the 1st ionisation energy decrease going down group 2?

Answer 32

The number of shells increase, so better atomic shielding and larger atomic radius

Question 33

Why do we use time of flight mass spectrometry?

Answer 33

Helps work out the mass of an atom

Question 34

Kinetic energy =?

Answer 34

1/2 m v^2

Question 35

Velocity=?

Answer 35

distance/ time

Question 36

Kinetic energy combined with velocity equation?

Answer 36

KE= 1/2 m d^2/t^2

Question 37

Time with kinetic energy equation?

Answer 37

t= d Square root: m/ 2KE