Atomic structure

Question 1

What is the mass and relative charge of protons , neutrons and electrons

Answer 1

Electrons - mass=1/1840 charge=-1
protons - mass=1 charge = +1
Neutrons- mass=1 charge=0

Question 2

What are the principles of a TOF mass spectrometer

Answer 2

Ionisation , Acceleration to give ions kinetic energy, ion drift , ion detection , data analysis.

Question 3

What is a plum pudding model ?

Answer 3

A sphere of positive charge with electrond scattered around

Question 4

What is an isotope ?

Answer 4

Atoms of the same element with the same number of protons but different number of neutrons.

Question 5

What does the mass spectrometer do?

Answer 5

The mass spectrometer gives (accurate) information about the relative isotopic mass and also the relative abundance of isotopes

Question 6

What can the mass spectrometer also do?

Answer 6

It can be used to identify elements and to determine relative molecular mass.

Question 7

What is relative atomic mass?

Answer 7

The average mass of one atom (of an element) to 1/12 of the mass of one atom of carbon-12

Question 8

What is relative molecular mass?

Answer 8

The average mass of a molecule to 1/12 of the mass of one atom of carbon-12

Question 9

What is vaporisation ?

Answer 9

Sample turns into gas

Question 10

What is ionisation?

Answer 10

High energy electrons knock off 1 electron from atom (gaseous) molecules
x(g)—– x^+ (g) + e^-
e^- + x (g) ——- x^+ (g) + 2e^-

Question 11

What is acceleration?

Answer 11

A negative plate (electric field) attracts positive ions so their velocity increases.

Question 12

What is ion drift?

Answer 12

The ions travel along the flight tube larger m/z ions take longer to reach detector (mass/charge)

Question 13

What is ion detection?

Answer 13

Positive ions hits negative plate
Collector——–positive ions so their velocity increases
x^+ +e- —– x = produces current
size of current is directly proportional to abundance.

Question 14

What is data analysis?

Answer 14

Time of flight converted into m/z. Size of current converted into abundance. Displayed as spectrum.
mass/charge= Ti

Question 15

What are the two type of ionisation techniques?

Answer 15

Electron impact , electronspray ionisation

Question 16

Describe the first technique?

Answer 16

High energy electrons from electricion gun fixed at sample , knock off an electron.
x(g)—– x^+ (g) + e^- OR
e^- + x (g) ——- x^+ (g) + 2e^-
used for elements and lower Mr molecules (relatively small mole)

Question 17

Describe the second technique?

Answer 17

Sample dissolved in volatile solvent. Injected through needle at high voltage - molecule gains a poroton (h^+)
x + H^+ —- XH^+
High Mr molecules including biological molecules.