1. 11 Na 12 Mg 1s 2 2s 2 2p 4 Wrong 22 Ti [Ar] 4s 2 3d 10 4p 2 ⃝ 17 Cl [Ar] 4s 1 3d 5  1s 2 2s 2 2p 6 3s 1 S orbital 1s 2 2s 2 2p 6 3s 2 [Ar] 4s 2 3d 9 p orbital1s 2 2s 2 2p 6 3s 2 3p 5 24 Cr [Ar] 4s 2 3d 2 8O8O 12 Mg 1s 2 2s 2 2p 4 Wrong 22 Ti [Ar] 4s 2 3d 10 4p 2 ⃝ 17 Cl [Ar] 4s 1 3d 5  1s 2 2s 2 2p 6 3s 1

2. Sub-atomic particles Protons – mass 1; charge +1 Electrons – mass 1 / 1840 ; charge –1 Neutrons – mass 1; charge 0 Atomic number – number of protons in nucleus Mass number – protons + neutrons in nucleus Electrons – (atomic number – charge)

3. Calculating numbers of each particle WHITEBOARDS ProtonsNeutronsElectrons 3 4 3 6 6 6 19 20 19

4. Chlorine How many protons does chlorine have in its nucleus? 17 How many electrons? 17 How many neutrons does chlorine have in its nucleus?

5. Isotopes Atoms of the same element can have different numbers of neutrons in the nucleus. The element has the same electron arrangement - so is chemically identical. The only difference between isotopes is the mass number. The isotopes name gives the mass number, for example, chlorine - 35 & chlorine - 37

6. Calculating numbers of each particle ProtonsNeutronsElectrons 17 18 17 17 20 17

7. Atomic mass of a mixture of isotopes The atomic mass of a mixture of isotopes of one element is the WEIGHTED AVERAGE of the atomic masses. Atomic mass = (9 x 35 + 3 x 37)/12 = 35.5 35 Cl 37 Cl 35 Cl 35 Cl 35 Cl 37 Cl 35 Cl 35 Cl 35 Cl 37 Cl 35 Cl 35 Cl

8. Practice Calculations 32 S 95 % 34 S 5 % (32 x 95 + 34 x 5)/100 =32.1 39 K 93.22 % 41 K 6.78 % (39 x 93.22 + 41 x 6.78)/100 =39.14 85 Rb 72.17 % 87 Rb 27.83 % (85 x 72.17 + 87 x 27.83)/100 =85.56

9. Relative masses Mass relative to 1 / 12 th mass of 1 atom carbon-12 Relative atomic mass: weighted mean of relative isotopic masses Relative molecular mass: sum of relative atomic mass in molecular formula Empirical – simplest ratio Molecular – atoms in a molecule

10. Mass spectroscopy Watch the video and animations – links via the online textbook Vaporisation Ionisation – E (g) + e - (high energy)  E + (g) + 2e - Acceleration – from +; through – grid Deflection – magnetic field Detection

11. Schematic diagram of mass spectrometer

12. Calculating atomic mass from mass spectra Relative atomic mass = weighted average of relative isotopic masses Chlorine: = (75 x 35) + (25 x 37) 100 = 35.5 + + Positive ion is detected 75% 50% 25%

13. Relative atomic mass tungsten Relative abundance 4:2:4:4 Relative atomic mass = 4x182+2x183+4x184+4x186 14 = 183.9 Why is this a plausible answer? 4244

14. Mass spectroscopy and molecular ions Molecules can undergo mass spectroscopy Three pieces of information can be found: – Mass of parent ion – Fragment pattern/fingerprint (can identify particular compounds) – Isotope ratio (calculating mass, source and distinguishing between natural and synthetic) C3H6O+C3H6O+ 58: CH 3 CH 2 CHO + 15: CH 3 + 29: CH 3 CH 2 + and CHO + 43: CH 2 CHO +

15. Mass spectra and archaeology The isotope 14 C is radioactive – it decays into 14 N While an organism is alive the proportion of carbon- 14 remains constant – as carbon compounds enter and leave On death the proportion of carbon-14 begins to decline The proportion of carbon-14 remaining can be used to estimate age up to about 60 000 years Other atomic isotopes can be used for longer dating e.g. U:Pb and K:Ar

16. Homework Due Friday 7 th October 2011 Mass spectrometry in space and sport p50-1 [Mark yourself using the online material] Review question p 61 & 62 Mass spectroscopy sheet