Chemistry: 1.1 Atomic Structure Part 1

Protons, neutrons and electrons

Charge: +1
Mass: 1
Location: nucleus

Mass: 1
Charge: 0
Location: nucleus

Mass: 1/2000
Charge: -1
Location: shells

Number of protons in the nucleus of an atom

Number of protons and neutrons in the nucleus of an atom

Atoms of the same element with a different number of neutrons

Same no of elections> same electron configuration> dictates chemical behaviour

Positively charged ion (cation)

A negative ion (anion)

Determining information about elements and compounds, it can be used to calculate relative atomic mass of an electrons or relative molecular mass of a compound

• ionisation

• acceleration

• separation of ions

• detection

Electron impact and electrospray ionisation

• sample injected into spectrometer and vaporised

• high energy electrons from electron gun fired at sample

• high energy electrons knock off an electron from each particle to form positive ions

Na (g) -> Na+ + e-

• sample dissolved in polar solvent

• injected through a fine hypodermic needle to give a fine mist

• tip of needle is attached to the positive terminal of a high voltage supply

• particles gain a proton (H+ ion) from the solvent to form positive ions

CH4 + H+ -> CH5+

Mass of ion= mass of element/compound

Mass of ion = mass of element/compound +1

An electric field is applied to accelerate the positive ions. This gives all the ions with the same charge the same kinetic energy

Lighter

Lighter ions reach the detector first

Heavier ions reach the detector last

To prevent other molecules in air colliding with the sample ions

Records the different ions as they arrive at the detector

They gain an electron at the detector to produce a current. The more ions of one type, the greater the current and bigger the peak

Relative abundance against mass to charge ratio

The relative atomic mass is an average

So it can be accelerated and detected

The mass of an isotope relative to 1/12th the mass of an atom of carbon 12

Weighted average mass of all the isotopes relative to 1/12th the mass of a carbon-12 atom

(Massxabundance of each isotope)/total abundance

Multiple each m/z by relative abundance and add them up, divide the whole thing by 100

M/z = 32 (CH3OH+)

Small amount of carbon 13 present

Molecule fragments until electron impact

The peak furthest to the right

Does not cause fragmentation of the molecular ion so fewer peaks are present

Gains hydrogen ion

| C12H25O6+

Carbon 13= C13H25O6

No fragmentation

M+

MH+