Atomic Structure

Question 1

Name and describe the sub-shells of an atom from lowest energy level to highest.

Give the general electron configuration.

Answer 1

S Sub-shell - only one type of S-orbital therefore only max 2 electrons in sub-shell
P Sub-shell - three types of P-orbital therefore max 6 electrons in sub-shell
D Sub-shell - five types of D-orbital therefore max 10 electrons in sub-shell
F Sub-shell - seven types of F-orbital therefore max 14 electrons in sub-shell

1s, 2s, 2p, 3s, 3p, 42, 3d, 4p, 52, 4d, 5p…

Question 2

What is different about the electron configuration for Cr, (Mo, W and Sg)?

What is different about the electron configuration for Cu, (Ag, Au and Rg)?

Answer 2

• Cr ‘spends’ energy to move an e- from 4s sub-shell to 3d sub-shell, to change the electron configuration from 4s2, 3d4 to 4s1, 3d5, as a half-full 3d sub-shell with a half-full 4s sub-shell is more stable than a full 4s sub-shell and almost half full 3d sub-shell due to less repelling electrons.
• Cu ‘spends’ energy to move an e- from 42 sub-shell to 3d sub-shell, to change the electron configuration from 4s2, 3d9 to 4s1, 3d10, as a full 3d sub-shell and half-full 4s sub-shell is more stable than a full 4s sub-shell and almost full 3d sub-shell due to less repelling electrons.

Question 3

Define Ionisation energy of an element.

What are the factors affecting Ionisation energy?

Answer 3

• The ionisation energy of an element is the amount of energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous ions.
• Atomic radius
• Nuclear shielding
• Nuclear charge

Question 4

Describe the steps in TOF Mass Spectrometry. (Electron impact vs Electrospray ionisation?)

Answer 4

1 - Ionisation - (electron impact)
- used for low Mr compounds.
- high energy electrons fired at sample, knocking electrons off each atom/molecules to form 1+ ions, (gaseous).
- Ionisation - (electrospray ionisation)
- used for high Mr compounds.
- sample dissolved in volatile solution, injected through fine hypodermic needle (charged with very high voltage to end of needle for +ve charge). particle gains proton from end of needle. solvent evaporates, leaving ions.

2 - Acceleration of ions -
- ions accelerated using an electric field so all ions have same kinetic energy, as attracted to negative plate.

3 - Seperation of charged ions -
- ion drift - ions enter flight tube, different time of flight depending on mass.

4 - Detection -
- detector -ve charged plate, current produced when ions pass plate and ‘take’ an electron. quantity of ion shown by size of current.

Question 5

How do you calculate Kinetic Energy and speed of ions? (TOF MS SPEC)

Answer 5

Ke=1/2mv^2

V=d/t

Question 6

Define Relative atomic mass and Relative molecular mass.

Answer 6

Ar = average mass of one atom of an element / 1/12th mass of one 12C atom.

Mr = average mass of one molecule / 1/12th mass of one 12C atom.

Question 7

Describe the …
- Br2
- Cl2
… mass spectrums formed from the TOF mass spectrometer.

Answer 7

Br2 -
- two small peaks at 79 and 81 in a ratio of 1:1.
- three main peaks at 158, 160 and 162, in a ratio of 1:2:1.

Cl2 -
- two small peaks at 35 and 37, in a ratio of 3:1.
- three main peaks at 70, 72 and 74, in a ratio of 9:6:1.