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Unit Objectives 1)understand the evolution of models of the atom: Dalton, Thomson, Rutherford, Bohr, the ‘quantum model 2) understand the meaning of mass.

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Presentation on theme: "Unit Objectives 1)understand the evolution of models of the atom: Dalton, Thomson, Rutherford, Bohr, the ‘quantum model 2) understand the meaning of mass."— Presentation transcript:

1 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

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

3 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

4 Fuse School Isotopes

5 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

6 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

7 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

8 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

9 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

10 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

11 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

12 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

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

14 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?

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

16 Fuse School RAM determination (4 mins)

17 ANOTHER MASS SPECTRUM? 20Ne 90.92% MASS SPECTRUM OF NEON 21Ne 0.26%
20Ne % 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

18 EXAMPLE CALCULATION (1)
Calculate the average relative atomic mass of neon using data on the previous page. Out of every 100 atoms are 20Ne , are 21Ne and are 22Ne Average = (90.92 x 20) + (0.26 x 21) + (8.82 x 22) = Ans. = 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

19 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 x (100-x) = 100 therefore x x = 3910 thus x = and x = 95 ANSWER There will be 95% 39K and 5% 41K

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

21 Right, ok now you try, see the handout

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