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Description
Flashcards by Tania Parvaiz, updated more than 1 year ago
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Created by Tania Parvaiz
over 8 years ago
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| Question | Answer |
| Why do we need to know the masses of atoms and molecules? | To calculate the Ar (relative atomic mass) |
| What 4 things can we find out using a mass spectrometer? | •Isotopic mass •Relative abundance of isotopes •Molecular mass •Ionisation energy |
| How do you calculate the Ar using a mass spectrometer? | Abundance of each isotope x mass ------------------------------------------ total abundance |
| What are the 4 stages of a ToF mass spectrometer? | •Ionisation •Acceleration •Ion drift •Detection |
| What are the 2 types of ionisation? | •Electron bombardment •Electrospray ionisation |
| What happens in electron bombardment and when is it used? | •High energy electrons are fired at the sample from an electron gun, which knocks off one electron from each atom •Used for isotopes/low Mr compounds |
| What happens in electrospray ionisation and when is it used? | •Sample is dissolved in volatile solvent and injected through nozzle and sprayed into vacuum chamber •Voltage is applied to end of nozzle (which is positively charged) so the particles gain a proton •Used for high Mr compounds |
| What is the equation for electron bombardment? | X(g) + e- -----> x+(g) - 2e- |
| What is the equation for electrospray ionisation? | X(g) + h+(g) -----> XH+(g) |
| What happens in the acceleration stage? | Ions are accelerated using an electric field so that all the ions have the same kinetic energy |
| What happens in the ion drift stage? | Lighter ions travel faster. Different ions have a different time of flight |
| What happens at the detector? | Detector is negatively charged. Current is produced when ions hit it - more ions means a bigger current is created. |
| What does a mass spectrum show? | Abundance against mass/charge ratio (m/z). Charge is usually 1 so m/z value is usually mass. |
| What does the amount of peaks signify on a mass spectrum? | Different isotopes |
| How can you tell how many shells an element has by looking at the periodic table? | Look at period number |
| How can you tell how many electrons on the outer shell an element has by looking at the periodic table? | Look at group number |
| What is the proper term for "shells"? | Principal energy levels |
| What is the proper term for "electrons on outer shell"? | Principal quantum number |
| What are orbitals? | Space where electrons are found |
| How many electrons do each type of orbitals hold? | 2 max |
| What are the 4 types of orbitals? | s, p, d and f |
| What are shells split into? | Sub-shells |
| What can an s sub-shell hold? | 1 s-orbital |
| What can a p sub-shell hold? | 3 p-orbitals |
| What can a d sub-shell hold? | 5 d-orbitals |
| How do electrons fill orbitals? (2) | •Lowest energy level first (4s before 3d) •Singly before pairing |
| Why does 4s fill before 3d? | 4s has slightly lower energy than 3d before it is filled meaning electrons go into 4s before 3d (Aufbau principle) |
| What are the 2 exceptions to the Aufbau principle? | Chromium and copper because they give one electron from 4s to 3d to make it either half full (Cr) or full (Cu) so it is stable |
| Why are 4s electrons lost before 3d electrons in transition metals when forming ions? | As soon as 4s and 3d sub-shells have electrons in them, their positions swap and 3d becomes lower in energy than 4s, which means 4s is the highest energy level. |
| What is the first ionisation energy? | The energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions. |
| What is the ionisation energy used for? | To break forces of attraction between positive nucleus and negative electron |
| When is the ionisation energy greater? (3) | •Distance from nucleus is smaller •Less electron shielding •Nuclear charge is greater |
| What happens to the first ionisation energy down any group? (2) | Decreases because: •More shells causing more shielding on the outer electron •Distance from nucleus of outer electron gets greater so force of attraction decreases Both of these factors outweigh the increase in nuclear charge |
| What happens to the first ionisation energy across any period? | Generally increases because nuclear charge increases but shielding and distance from nucleus remain the same. Drops between groups 2 & 3 and groups 5 & 6 |
| Why is there a drop between groups 2 & 3 in first ionisation energy? | The electron removed from the p orbital is further from the nucleus and has more shielding so first ionisation energy is lower |
| Why is there a drop between groups 5 & 6 in first ionisation energy? | Group 6 elements outer electron is removed from a paired orbital and so the force of repulsion makes it easier to remove. Group 5 elements outer electron removed from singly-occupied orbital. |
| How can you use ionisation energies to identify what element is in the graph? | Amount of electrons removed before big jump = group number Number of shells = period number |
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