Subatomic Particles Isotopes And Mass Spectrometry

proton — relative mass 1, charge +1; neutron — relative mass 1, charge 0; electron — relative mass 1/1836 (or ≈ 0), charge −1

protons = 26; neutrons = 56 − 26 = 30; electrons = 26 − 3 = 23

an electron has a mass of about 1/1836 that of a proton; this is negligibly small compared to protons and neutrons, so it does not affect the mass number

atoms of the same element with the same number of protons / same atomic number; but different numbers of neutrons / different mass numbers

isotopes have the same number of electrons / same electronic configuration; chemical properties depend on the outer electrons, so the reactions are the same

• ionisation — sample bombarded with high-energy electrons to form positive ions - acceleration — positive ions accelerated by an electric field to give equal kinetic energy - deflection — ions deflected by a magnetic field according to m/z; lighter or more highly charged ions deflect more - detection — ions hit a detector that records relative abundance against m/z

Finding the relative atomic mass $${A}_{r}=\frac{(24\times 78.99)+(25\times 10.00)+(26\times 11.01)}{100}$$ $${A}_{r}=\frac{2432.02}{100}$$ $${A}_{r}=24.32$$ The relative atomic mass is 24.32.

m/z = 26; the ion has mass 52 and charge 2+, so m/z = 52 ÷ 2 = 26

Mr = 58; matches C₄H₁₀ (butane) since (4 × 12) + (10 × 1) = 58

H–³⁵Cl at m/z = 36; H–³⁷Cl at m/z = 38; relative heights 3 : 1

chlorine has two isotopes, ³⁵Cl and ³⁷Cl; each atom in Cl₂ may be either isotope, giving three possible combinations; ³⁵Cl–³⁵Cl, ³⁵Cl–³⁷Cl and ³⁷Cl–³⁷Cl all give different molecular masses

• element Y is chlorine, existing as Cl₂ - the 9 : 6 : 1 pattern matches two isotopes in a 3 : 1 ratio (³⁵Cl 75%, ³⁷Cl 25%) - m/z 70 corresponds to ³⁵Cl–³⁵Cl⁺; m/z 72 corresponds to ³⁵Cl–³⁷Cl⁺; m/z 74 corresponds to ³⁷Cl–³⁷Cl⁺ - the 6 for the mixed peak arises from two equivalent combinations (3 × 1 + 1 × 3) - relative atomic mass: $${A}_{r}=\frac{(35\times 75)+(37\times 25)}{100}$$ $${A}_{r}=\frac{3550}{100}=35.5$$ chlorine has only two stable isotopes, so only three pair combinations exist; no other molecular ion m/z values are possible