atomic structure

John dalton

atoms are solid spheres, different spheres make up different elements

J.J Thompson

discovered an electron.

Positively charged pudding with negative electrons embedded inside it.

Ernest Rutherfod

conducted gold foil experiment

• Fired positively charged alpha particles at a thin sheet of gold.

• Plum pudding suggested that most particles would be deflected by ‘pudding’. However most passed straight through, with only a small n.o being deflected.

• Development of the nuclear model - positively charged nucleus surrounded by a cloud of electrons in mostly empty space.

Niels Bohr

discovered that electrons exist in shells/ orbitals.

When electrons move between shells electromagnetic radiation is emitted or absorbed.

relative atomic mass

Average mass of an atom compared to one twelfth of the mass of one atom of carbon-12.

Relative molecular mass

Average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12.

Relative isotopic mass

Average mass of an isotope compared to one twelfth of the mass of an atom of carbon-12.

ELECTROSPRAY IONISATION

• sample is dissolved and pushed through a small nozzle at high pressure.

• High voltage is applied, causing each particle to gain a H+ ion.

• Sample is turned into a gas made up of positive ions.

E.g M(g) + H+ = MH+(g)

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

ACCERLERATION

• positively charged ions are accelerated by an electric field so they all have the same kinetic energy.

  Lighter ions move faster than heavier ions.

ION DRIFT

Ions enter region with no electric field, drift through it.

Lighter ions move faster than heavier ions.

DETECTION

Detector detects charged particles and a mass spectrum.

Electron impact

• sample is vaporised

• ‘electron gun’ fires high energy electrons at sample

• knocks one electron off each particle, so they become 1+ ions

  E.g Ti(g) = Ti+(g) + e-

used for elements and substances with low formula mass

can cause larger organic molecules to fragment.

first ionisation energy

energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.

second ionisation energy

energy needed to remove one mole of electrons from each ion in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions.