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The Structure of the Atom.

Extracts from this document...

Introduction

The Structure of the Atom. Basic Atomic Particles : Atoms are made up of the following particles : Protons : Protons are positively charged particles with a mass of one atomic mass unit. They are found in the nucleus at the centre of the atom structure. Neutrons : Neutrons are not charged and have a mass of one atomic mass unit. They are found, with protons at the centre of the atom. Electrons : Electrons are negatively charged particles with a mass of 1/1846th of an atomic mass unit. They are arranged in shells around the central nucleus. Useful definitions for atomic structure : Atomic number (Z) : The number of protons in the nucleus of an atom but is also equal to the number of electrons in the same atom (because atoms don't carry an overall charge - the positives balance the negatives!). Mass Number, (A) (or atomic mass) : The number of neutrons and protons in the nucleus of one atom of the element The atomic number and mass number of a particular element can be found from the periodic table. The atomic number is always displayed to the bottom left of the symbol for the element. The mass number is always displayed to the top left of the symbol for the element. ...read more.

Middle

During the mass spectrum of any sample, ionisation and acceleration take place continually. The magnetic field starts at its lowest setting before increasing gradually to its highest setting. The ions are detected by the sensitive screen as they pass through the mass spectrometer at the correct magnetic field strength. This very small detection is photomultiplied before being sent to a suitable detector. What does a mass spectrum look like? Double Ionisation. Please note : Ionisation in a mass spectrometer is a precarious business. Atoms are passed into a field of fast moving electrons. Most of the time only one electron will be removed from the atoms at this point : e.g. Cl + e- ==> Cl+ + 2e- However, in some cases two electrons may be removed from the same atom. Cl + e- ==> Cl2+ + 3e- This leaves us with a dipositive ion (2+) rather than a unipositive one (1+) and the mass to charge (m/z) ratio of these ions will be half of the mass to charge ratio of the (1+) ion. Q11. A scientist wants to find the exact RAM of titanium. A sample of titanium was placed into a mass spectrometer the following results were obtained.: Mass to charge ratio (m/z) ...read more.

Conclusion

Q3. Draw the low resolution mass spectra you would expect for the following compounds, clearly showing the molecularions that would form. a) CH2CHBr b) CH2CHCl c) CH2BrCH2Br d) CH2ClCH2CL Ans : a) Should contain two peaks of equal size at 106 (containing 79Br) and 108 (containing 81Br) b) Should contain a large molecularion peak at 62 (containing 35Cl) and a smaller molecularion peak at 64 (containing 37Cl) that is one third of the size of the other peak. c) There should be three molecularion peaks in this spectrum, one at 186 (containing two 79Br atoms), one at 188 (containing one 79Br and one 81Br - there are two possibilities as to how this might arise) and one peak at 190 (containing two 81Br atoms). The heights of these peak should be roughly in the ratio (1:2:1) reflecting the probability of each occuring. d) There should be three molecularion peaks in this spectrum, one at 98 (containing two 35Cl atoms), one at 100 (containing one 35Cl and one 37Cl - there are two possibilities as to how this might arise) and one peak at 102 (containing two 37Cl atoms). The heights of these peak should be in the ratio (0.5625:0.375:0.0625) reflecting the probability of each occuring. (0.75 x 0.75 = 0.5625) : ((0.75 X 0.25) X2 = 0.375), (0.25 X 0.25 = 0.0625) ...read more.

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