Unit Objectives 1)understand the evolution of models of the atom: Dalton, Thomson, Rutherford, Bohr, the ‘quantum model 2) understand the meaning of mass number, atomic (proton) number. 3) be able to write and work with full atomic symbols 4) be able to calculate relative atomic, molecular and formula mass

Refreshing some Old Terminology Mass Spectrometer Isotopes and ions R.A.M. (Relative Atomic Mass)

MASS NUMBER AND ATOMIC NUMBER Atomic Number (Z) Number of protons in the nucleus of an atom Mass Number (A) Sum of the protons and neutrons in the nucleus Mass Number (A) PROTONS + NEUTRONS Na 23 11 Atomic Number (Z) PROTONS

Fuse School Isotopes https://www.youtube.com/watch?v=o7Kpk3al_uo

A MASS SPECTROMETER DETECTOR ION SOURCE ANALYSER A mass spectrometer consists of ... an ion source, an analyser and a detector. PARTICLES MUST BE IONISED SO THEY CAN BE ACCELERATED AND DEFLECTED

HOW DOES IT WORK? IONISATION DETECTOR ION SOURCE ANALYSER IONISATION gaseous atoms (a flame is provided to vaporise atoms) are bombarded by electrons from an electron gun and are IONISED sufficient energy is given to form ions of 1+ charge

HOW DOES IT WORK? IONISATION DETECTOR ION SOURCE ANALYSER IONISATION gaseous atoms are bombarded by electrons from an electron gun and are IONISED sufficient energy is given to form ions of 1+ charge ACCELERATION ions are charged so can be ACCELERATED by an electric field

HOW DOES IT WORK? IONISATION DETECTOR ION SOURCE ANALYSER IONISATION gaseous atoms are bombarded by electrons from an electron gun and are IONISED sufficient energy is given to form ions of 1+ charge ACCELERATION ions are charged so can be ACCELERATED by an electric field DEFLECTION charged particles will be DEFLECTED by a magnetic or electric field

HOW DOES IT WORK? IONISATION DETECTOR ION SOURCE ANALYSER IONISATION gaseous atoms are bombarded by electrons from an electron gun and are IONISED sufficient energy is given to form ions of 1+ charge ACCELERATION ions are charged so can be ACCELERATED by an electric field DEFLECTION charged particles will be DEFLECTED by a magnetic or electric field DETECTION by electric or photographic methods

HOW DOES IT WORK? IONISATION DETECTOR ION SOURCE ANALYSER IONISATION gaseous atoms are bombarded by electrons from an electron gun and are IONISED sufficient energy is given to form ions of 1+ charge ACCELERATION ions are charged so can be ACCELERATED by an electric field DEFLECTION charged particles will be DEFLECTED by a magnetic or electric field DETECTION by electric sensor

HOW DOES IT WORK? - Deflection 20Ne 21Ne 22Ne HEAVIER ISOTOPES ARE DEFLECTED LESS the radius of the path depends on the value of the mass/charge ratio (m/z) ions of heavier isotopes have larger m/z values so follow a larger radius curve as most ions are 1+charged, the amount of separation depends on their mass

HOW DOES IT WORK? - Deflection 20Ne 21Ne 22Ne HEAVIER ISOTOPES ARE DEFLECTED LESS the radius of the path depends on the value of the mass/charge ratio (m/z) ions of heavier isotopes have larger m/z values so follow a larger radius curve as most ions are 1+charged, the amount of separation depends on their mass if an ion acquires a 2+ charge it will be deflected more; its m/z value is halved

Mass spectrum of Cl2: m/e ratio Corresponding ion 35 35Cl+ 37 37Cl+ 70 72 35Cl ─ 37Cl+ 74 37Cl ─37Cl+

Cl 35 17 37 The two isotopes of chlorine are written as: Cl-35 and Cl-37, from the spectrograph earlier Cl-35 was 75% and the other 25%, what is the weighted average atomic mass?

Cl has 2 isotopes: Cl-35 and Cl-37 Relative abundance Cl-35 75% Cl-37 25%

Fuse School RAM determination (4 mins) https://www.youtube.com/watch?v=aqfQKzbTCVo

ANOTHER MASS SPECTRUM? 20Ne 90.92% MASS SPECTRUM OF NEON 21Ne 0.26% 19 20 21 22 23 20Ne 90.92% 21Ne 0.26% 22Ne 8.82% MASS SPECTRUM OF NEON THE positions of the peaks gives atomic mass THE peak intensity gives the relative abundance

EXAMPLE CALCULATION (1) Calculate the average relative atomic mass of neon using data on the previous page. Out of every 100 atoms... 90.92 are 20Ne , 0.26 are 21Ne and 8.82 are 22Ne Average = (90.92 x 20) + (0.26 x 21) + (8.82 x 22) = 20.179 Ans. = 20.18 100 TIP In calculations of this type... multiply each relative mass by its abundance add up the total of these values divide the result by the sum of the abundances

Can we calculate the % composition if we know the isotopes ? Naturally occurring potassium consists of potassium-39 and potassium-41. Calculate the percentage of each isotope present if the average is 39.1. Assume there are x nuclei of 39K in every 100; so there will be (100-x) of 41K so 39x + 41 (100-x) = 39.1 100 therefore 39 x + 4100 - 41x = 3910 thus - 2x = - 190 and x = 95 ANSWER There will be 95% 39K and 5% 41K

Calculate the relative atomic mass of the following – give your answers to 3 significant figures Bromine : 79 Br 50% , 81 Br 50% Copper : 63 Cu 69% , 65 Cu 31% Zirconium : 90 Zr 51.5% , 91 Zr 11.2%, 92 Zr 17.1%, 94 Zr 17.4%, 96 Zr 2.8% Lead : 204 Pb 1.5% , 206 Pb 23.6%, 207 Pb 22.6%, 208 Pb 52.3% Neon : 20 Ne 90.9% , 21 Ne 0.2%, 22 Ne 8.9% 63.6 91.3 207. 20.2

Right, ok now you try, see the handout