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41 Cards in this Set
- Front
- Back
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What are the three Sub-atomic particles? |
Proton Neutron Electron |
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What are the positions of the three Sub-atomic particles? |
Protons are found in the nucleus. Neutrons are found in the nucleus. Electrons are found in orbitals. |
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What are the relative charges of the three Sub-atomic particles? |
The relative charge of a proton is +1. The relative charge of an electron is -1. The relative charge of a neutron is 0. |
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What are the relative masses of the three Sub-atomic particles? |
The relative mass of a proton is 1. The relative mass of a neutron is 1. The relative mass of an electron is 0. |
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What is Time of Flight mass spectrometry used for? |
The mass spectrometer can be used to determine all the isotopes present in a sample of an element and to therefore identify elements. |
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What are the conditions for Time of Flight mass spectrometry? |
It needs to be under a vacuum otherwise air particles would ionise and register on the detector. |
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What are the four stages of Time of Flight mass spectrometry? |
Ionisation Acceleration Flight Tube Detection |
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What are the two different types of ionisation? |
Electron impact Electro spray ionisation |
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What happens during electro spray ionisation? |
The sample is dissolve in a volatile, polar solvent. It is then injected through a fine hypodermic needle giving a fine mist or aerosol. The tip of the needle has high voltage. At the tip of the needle the sample molecule, M, gains a proton, H+, from the solvent forming MH+. M(g) + H+ ➞ MH+(g) The solvent evaporated away while the MH+ ions move towards a negative plate. |
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When is electro spray ionisation used? |
Electro spray ionisation is used preferably for larger organic molecules. The softer conditions of this technique mean fragmentation does not occur. |
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What happens during electron impact ionisation? |
A vaporised sample is injected at low pressure. An electron gun fires high energy electrons at the sample. This knocks out an outer electron. Forming positive ions with different charges. |
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What happens during acceleration? |
Positive ions are accelerated by an electric field to a constant kinetic energy. |
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What happens in the flight tube? |
The positive ions with m/z values will have the same kinetic energy as those with larger m/z values and will move faster. The heavier particles take longer to move through the drift area. The ions are distinguished by different flight times. |
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What happens during detection? |
The ions reach the detector and generate a small current, which is fed to a computer for analysis. The current is produced by electrons transferring from the detector to the positive ions. |
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How do you calculate the time of flight? |
t = d/v t = time of flight (s) d = length of flight tube (m) v = velocity of the particle (m/s)
v = √2KE/m v = velocity of the particle (m/s) m = mass of the particle (kg) KE = kinetic energy of the particle (J) |
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What does the size of the current tell us? |
The size of the current is proportional to the abundance of the species. |
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How do you calculate the mass of one ion? |
Mass of one ion = mass of one mole ÷ The Avogadro constant |
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What is the parent ion or molecular ion? |
The parent or molecular ion is the largest peak of a series of peaks given when a molecule is put through a mass spectrometer with an electron impact ionisation stage and is subsequently fragmented giving a series of peaks. The peak with the largest m/z value will be equal to the relative molecular mass of the molecule. |
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What happens if a molecule is put through a mass spectrometer with electro spray ionisation? |
If a molecule is put through a mass spectrometer with electro spray ionisation, then fragmentation will not occur. There will be one peak that will equal the mass of the MH+ ion. It will therefore be necessary to subtract 1 to get the Mr of the molecule. |
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What is the atomic number? |
The atomic number is the number of protons in the nucleus. |
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What is the mass number? |
The mass number is the number of protons and neutrons in the nucleus. |
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What are the isotopes? |
Isotopes are atoms with the same number of protons, but different numbers of neutrons. |
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How do you calculate R.A.M? |
R.A.M = Σ(isotope mass × % abundance) ÷ 100 R.A.M = Σ(isotope mass × relative abundance) ÷ total relative abundance |
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What was the Bohr model of the atom? |
2 electrons in the first shell and 8 on the second with the electrons in spherical orbits. |
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What are the Principle energy levels? |
1, 2, 3 and 4. |
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What are the sub energy levels called? |
S holds up to 2 electrons. P holds up to 6 electrons. D holds up to 10 electrons. F holds up to 14 electrons. |
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Which sub-levels are in Principle level 1? |
1s |
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Which sub-levels are in Principle level 2? |
2s, 2p |
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Which sub-levels are in Principle level 3? |
3s, 3p, 3d |
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Which sub-levels are in Principle level 4? |
4s, 4p, 4d, 4f |
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Why does 4s get filled up before 3d? |
An atom fills up the sub shells in order of increasing energy and 3d has higher energy than 4s and do gets filled after the 4s. |
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What is ionisation energy? |
The first ionisation energy is the enthalpy change when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge. |
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What is second ionisation energy? |
The second ionisation energy is the enthalpy change when one mole of gaseous ions with a single positive charge forms one mole of gaseous ions with a double positive charge. |
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What are the factors that affect ionisation energy? |
The more protons in the nucleus the greater the attraction. The larger the atomic radius, the further the outer electrons are from the nucleus and the weaker the attraction of the nucleus. The more shielding of inner electrons, the weaker the attraction between the nucleus and the outer electrons. |
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Why are successive ionisation energies always larger? |
The second ionisation energy of an element is always bigger than the first ionisation energy. When the first electron is removed a positive ion is formed. The ion increase the attraction on the remaining electrons and so the energy required to remove the next electron is larger. |
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What is a periodicity? |
A repeating pattern across a period. |
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Why does Helium have the largest first ionisation energy? |
Its first electron is in the first shell closest to the nucleus and has no shielding effects from inner shells. He has a bigger first ionisation energy than H as it had one more proton. |
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Why do first ionisation energies decrease down a group? |
As one goes across a period the electrons are found in shells further from the nucleus and are more shielded, so the attraction of the nucleus becomes smaller. |
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Why is there a general increase in first ionisation across a period? |
As one goes across a period the electrons are being added to the same shell which has the same distance from the nucleus and same shielding effect. The number of protons increases, however, making the effective attractions of the nucleus greater. |
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Why does Na have a much lower first ionisation energy than Neon? |
This is because Na will have its outer electron in a 3s shell further from the nucleus and is more shielded. Na’s outer electron is easier to remove and has a lower ionisation energy. |
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Why is there a small drop in the general trend of first ionisation energy from P to S? |
With sulphur there are 4 electrons in the 3p sub shell and the 4th is starting to doubly fill the first 3p orbital. When the second electron is added to a 3p orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove. |
