3.1.1 Atomic structure

Question 1

What is first ionisation energy

Answer 1

the energy required to remove 1 mole of electrons from one mole of gaseous atoms to form 1 mole of 1+ Gaseous ions

Question 2

ionisation energy equation is

Answer 2

(n-1)+ n+
X* —> X * + e-

with n being the nth ionisation energy
so for 2nd ionisation energy its 1+ and 2+

Question 3

what are the 4 factors effecting ionisation energy

Answer 3

.Charge of nucleus - higher charge of nucleus= greater force of attraction between electron = Greater I.E

. Distance from nucleus(atomic radius)- greater distance = less I.E

. Shielding - greater shielding = less I.E

. Charge of ion/atom - harder to remove electron from a greater charged ion since greater forces of attraction so greater positive charge leads to more I.E required

Question 4

5 steps in TOF mass spectrometry

Answer 4

1. Ionisation
   2.acceleration
   3.Ion drift
   4.detection
   5.Analysis

Question 5

describe ionisation in TOF mass spectrometry

Answer 5

Electron impact
* vaporised sample injected at low pressure
*An electron gun fires high energy electrons at the sample
*This knocks out an outer electron forming ions of 1+ charge

Electrospray Ionisation
* sample dissolved in a volatile, polar solvent
* injected through a fine needle giving a fine mist or aerosol
* tip of needle has high voltage
* at tip of the needle the sample molecule, M ,gains a proton, H+, from the solvent forming MH+

• The solvent evaporates away while the charged sample molecule’s ions move towards a negative plate
  It needs to be under a vacuum or air particles would ionise and register on the detector

Electron impact is used for elements and substances with low formula mass. Electron impact can cause larger organic molecules to fragment.

Electro spray ionisation is used preferably for larger organic molecules. The ‘softer’ conditions of this technique mean fragmentation does not occur.

Question 6

Describe acceleration in TOF mass spectrometry

Answer 6

*Positive ions are accelerated by an electric field since the ions are attracted to the electric field caused by the negatively charged plate
*To a constant kinetic energy

Given that all the particles have the same kinetic energy, the velocity of each particle depends on its mass. Lighter particles have a faster velocity, and heavier particles have a slower velocity.

Question 7

Describe ion drift in TOF mass spectrometry

Answer 7

*The positive ions with smaller m/z values will have the same kinetic energy as those with larger m/z and will move faster.
*The heavier particles take longer to move through the drift area / flight tube
*The ions are distinguished by different flight times

Question 8

Describe the detection stage in TOF mass spectrometry

Answer 8

The ions reach the detector and generate a small current, which is fed to a computer for analysis. The current is produced by electrons transferring from the detector to the positive ions. The size of the current is proportional to the abundance of the species

Question 9

Write the electron configuration for chromium

Answer 9

ends in 3d5 4s1

Question 10

Write the electronic configuration for copper

Answer 10

ends in 3d10 4s1

Question 11

what is mass spectrometry used for

Answer 11

Mass spectrometry can be used to identify elements. Mass spectrometry can be used to determine relative molecular mass.
a mass spectrometry shows the rfm and its abundance

Question 12

define relative atomic mass

Answer 12

the average mass of 1 atom of an element relative to 1/12 of a carbon 12 atom

Question 13

state how the mr of a compound is obtained on a mass spectra

Answer 13

by the highest m/z value

Question 14

what is a transitional metal

Answer 14

elements with partially filled d orbitals

Question 15

Name 2 trends in first ionisation energy

Answer 15

1st ionisation energies of elements down a group of periodic table decrease
1st ionisation energies of elements across a period generally increase

Question 16

What provides evidence for shells structure of atoms?

Answer 16

Graph of successive ionisation energies gives evidence due to greater jumps after removing certain amounts of electrons - this is due to a change in subshellls

Question 17

how can you tell the group of an element by the successive ionisation energy

Answer 17

if the biggest change in ionisation energy is after nth ionisation energy , nth ionisation energys number is the group that the element belongs to

Question 18

describe the change in ionisation energy across a period

Answer 18

shielding similar but nuclear charge increase=lower at.radius = greater IE

Question 19

where is mass spectra used

Answer 19

in sports industry detecting for illegal substances in the blood