Chemistry - Isotopes and Mass Spectrometry

Isotopes

Atoms of the same element with different atomic mass

Isotopes properties

-Same atomic number (same element)

-Different mass numbers

-Chemically similar, but may have different physical properties

Isotopes types

-Stable isotopes: Do not decay (e.g., Carbon-12)

-Radioactive isotopes: Unstable, emit radiation (e.g., Carbon-14)

Why sometimes radioactive?

-combination of P⁺and N^o does not provide sufficient strong nuclear force to hold the nucleus together indefinitely.

-Eventually it will rearrange itself and emit a particle and radiation as it becomes stable.

Mass spectrometry

-Technique which measures atomic and molecular mass

-Also can be used to find isotopic abundance

Mass Spectrometry allows for:

-Separation of individual isotopes of an element sample

-Determination of the mass of each isotope, relative to C-12

-Calculation of the relative abundances of the isotopes in the sample

Mass spectrometry process

-The sample is vaporised and ionised (allows them to be manipulated by electric and magnetic fields.)

-Ions are accelerated by an electric field and then separated based on their mass-to-charge ratio (m/z) using a magnetic or electric field.

-A detector records the number of ions for each mass-to-charge ratio, generating a mass spectrum.

Size of the charge’s impact on deflection

Greater the charge the larger the deflection

mass of particle’s impact on the degree of deflection

Larger the mass the less the deflection

Mass spectra graphs

Output of mass spectrum, peaks for each of the ions that are detected for each ratio

if no scale %abundance

Peak height/total peak heights x 100