7. Modern analytical techniques (MASS SPECTROMOTERY+ IR)

Particles Relative mass Charge Proton: 1 + 1 Neutron: 1 0 Electron: 1/1840 -1

Total number of protons and neutrons in an atoms nucleus

Number of protons in the nucleus –> given the letter Z

Number of protons and neutrons in an atom –> given the letter A

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

The mass of an atom of an isotope relative to one twelfth of the mass of one atom of carbon -12

The average mass of an atom of an element relative to one twelfth of the mass of one atom of carbon -12

1) identifying elements on other planets and their isotopes 2) drug testing in sports to identify chemicals in the blood 3) quality control in the pharmaceutical industry 4) radioactive dating (carbon - 14) to determine age of fossils etc.

Vaporisation Ionisation Acceleration Deflection Detection

Ionisation - Heated metal coil gives off electrons that are attracted to the positively charged plate above it. Gaseous sample is bombarded by electrons to form 1+ ions.

Accelerated using an electric field

Charged particles deflected by a magnetic field - with an electromagnet

Mass of ion - lighter ions that have smaller m/z ratio are deflected more than heavier ones Charge on the ion- 2+ ions are deflected more than a +1 ion. This halves the m/z (mass/charge) value but the abundance stays the same.

The mass of the isotope –> mass / charge but charge is often just +1 so its just mass

The beam of ions passing through the machine is detected electrically. –> when the beam of ions hits a negative plate its charge is neutralised by an electron jumping from the metal on to the ion. That leaves a space amongst the electrons in the metal, and the electrons in the wire shuffle along to fill it. –> A flow of electrons in the wire is detected as an electric current which can be amplified and recorded. The more ions arriving, the greater the current.

Lines represent different isotopes in that element

When a molecule becomes ionised to form a molecular ion (M+) which is unstable and can fragment into different pieces

It shows the different fragments produced when the molecular ion breaks up

In the ionisation chamber, an electron is knocked off the molecule to form a molecular ion - Cl2+. This can then form a chlorine atom and cl+ ions. As the atom has no charge it is not included in mass spectra. The cl+ atom will form lines at 35 and 37 in the ratio 3:1. However, you will also get lines for the unfragmented (cl2) +. This ion could either be from the isotopes: chlorine 35 and chlorine 35 = 70 chlorine 35 and chlorine 37 = 72 - this combo is twice as likely to occur compared to the others chlorine 37 and chlorine 37 = 74 Relative intensity: 3/4 x 3/4 = 9/16 3/4 x 1/4 = 3/16 + 3/16 = 6/16 1/4 x 1/4 = 1/16 Therefore, you get lines in the ratio: 9:6:1

• exhibits a 1:2:1 ratio • this is because there are two naturally occurring stable isotopes of bromine, 79Br and 81Br. Both of these isotopes are present in a 1:1 ratio So: 79Br+ 79Br =158 79Br + 81Br =160 - this combo is twice as likely to occur that the others 81Br + 81Br =162 Relative intensity 0.5 x 0.5 =0.25 0.5 x 0.5 =0.25 + 0.25 = 0.50 0.5 x 0.5 =0.25 So 0.25: 0.50: 0.25 = 1:2:1

M+ ion is the heaviest so it is furthest to the right

The relative molecular mass of the molecule

to prevent interference from air molecules - Molecular fragments could not exist otherwise

No, not always. You divide by the total abundance which is not always 100%. Check by adding up total abundance either from a table or graph