3.1.1 - Atomic structure Flashcards
Describe the TOF spectrometry process (5)
Uses electron gun preparation
- Sample is dissolved in volatile solvent
- Sample is passed through an electron gun
- Sample loses an electron to form positive ion
- Ions accelerated to constant kinetic energy via a negative plate (bigger ions move slower)
- When ion hits detector it creates a current (gains electron)
Describe electrospray ionsation
- Sample dissolved in volatile sample
- Passed through hypodermic needle
- Gains proton
Define the term relative atomic mass
Average mass of 1 atom of a element divided by 1/12 the mass of one atom of carbon-12
Describe J.J Thomson’s (1897) findings
Plum pudding model - negative electrons in a “pudding” of positive charge
Describe Rutherford’s (1909) gold leaf experiment and findings
- Discovered a very small, positively charged nucleus
- Fired positive alpha particles at thin gold leaf, most went through (mostly empty space), some deflected (hit positive nucleus)
Describe Niel Bohr’s (1913) findings
Proposed electrons where in fixed energy shells as opposed to a cloud
Describe the trend in ionisation energies down Group 2
- Decreases
- Ions get bigger, highest electron subshell further away from nucleus.
- Weaker force of attraction of ion to lost electron
State which period 3 element has the highest melting point
- Silicon
- Has covalent bonds
- Takes a lot of energy to break these bonds
How to do relative abundance questions
Do m/z x relative abundance line (e.g. 124x2 + 126x4 etc) divided by total abundance lines.
Why would the relative abundance value be different to the periodic table value?
Some isotopes may not be present
The mass spectrum of tellurium also has a small peak at m / z = 64. Explain the existence of this peak.
Due to the existence of the 128Te2+ ion
What is measured in a TOF spectra?
- m/z (mass to charge ratio)
- relative abundance
Explain how this current is generated.
Electrons transferred from detector to the positive ion
