Atomic Structure

Question 1

TOF Ionisation 2 ways

Answer 1

electron impact:
•A vaporised sample is injected at low pressure
•An electron gun fires high energy electrons at the sample
•This knocks out an outer electron

Electro Spray Ionisation
• sample dissolved in volatile, polar solvent
• injected through a fine needle giving a fine mist
• tip of needle has high voltage
• at tip of the needle the sample molecule, gains a proton, H+
• solvent evaporates away while h+ ions move towards a negative plate

Question 2

TOF Acceleration

Answer 2

•Positive ions are accelerated by an electric field •To a constant kinetic energy

Question 3

TOF Flight Tube

Answer 3

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

Question 4

TOF Detection

Answer 4

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.
size of the current is proportional to the abundance of the species

Question 5

first ionisation energy

Answer 5

enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge

Question 6

Factors that affect Ionisation energy

Answer 6

• attraction of nucleus
• shielding
• distance of electrons from nucleus

Question 7

Why are successive ionisation energies always larger?

Answer 7

eg 2nd is bigger than 1st

• When the first electron is removed a positive ion is formed.
• ion increases the attraction on the remaining electrons –so the energy required to remove the next electron is larger.

Question 8

Why has Helium the largest first ionisation energy?

Answer 8

Its first electron is in the first shell closest to the nucleus and has no shielding effects from inner shells. He has a bigger first ionisation energy than H as it has one more proton

Question 9

Why do first ionisation energies decrease down a group?

Answer 9

As one goes down a group, the outer electrons are found in shells further from the nucleus and are more shielded so the attraction of the nucleus becomes smaller

Question 10

Why is there a general increase in first ionisation energy across a period?

Answer 10

as one goes across a period the electrons are being added to the same shell which has the same distance from the nucleus and same shielding effect. The number of protons increases, however, making the effective attraction of the nucleus greater.

Question 11

Al Ionisation trend

Answer 11

The electrons in the 3p subshell are slightly easier to remove because the 3p electrons are higher in energy and are also slightly shielded by the 3s electrons

Question 12

S ionisation trend

Answer 12

• With sulphur there are 4 electrons in the 3p sub shell and the 4th is starting to doubly fill the first 3p orbital.
• When the second electron is added to a 3p orbital there is a slight repulsion between the two negatively charged electrons
• makes the second electron easier to remove.

Question 13

mole

Answer 13

the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12

Question 14

Relative atomic mass

Answer 14

the average mass of one atom compared to one twelfth of the mass of one atom of carbon-12