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Chemistry 1.5
AS edexcel chemistry - atomic structure
| Question | Answer |
|---|---|
| What is an electron configuration and what is the maximum? | The arrangement of electrons in energy levels called shells. Maximum is 2,8,18,32 |
| What is the principal quantum number? | Describes the principal energy level and determines the size of the orbital and distance from the nucleus. First energy level: n=1, second energy level: n=2 |
| An electron further from the nucleus has higher / lower energy? | Higher |
| What is the Heisenberg uncertainty principal? | That you can't determine the position and momentum of an electron at the same time |
| What is the quantum mechanical model? | The idea that electrons exist in orbitals - regions of space around the nucleus in which there is a 90% chance of finding an electron at any given time in a particular state. |
| What does shape of the atomic orbital depend on? | The wave function for an electron |
| What are features of the electrons in one orbital? | Same energy, opposite spin (one spin up, one spin down), 2 electrons maximum |
| Describe and draw an s orbital | Spherical, one found in every principal energy level |
| Describe and draw the p orbitals | Three p orbitals in a p subshell, dumb-bell shaped, at right angles to each other, one found in every principal energy level excluding the first, Px, Py, Pz |
| Describe and draw the d orbitals | There are five d orbitals in a d subshell, various shapes - Dxy, Dxz, Dyz, Dx2-y2, Dz2 |
| What is the aufbau principle? | The method of filling subshells from low to high energy.S orbitals filled before p orbitals, filled before d orbitals. Further from nucleus, energy levels get closer. 4s and 3d overlap - 4s filled first, lost first in ionisation, 3d written first |
| What does the term 'penetrating' mean? | S electrons are more penetrating towards the nucleus than p electrons as they are found closer to the nucleus and so experience a greater effective nuclear charge. |
| What is the Pauli exclusion principal? | Each orbital can hold a maximum of two electrons with opposite spin (one spin up, one spin down) |
| What is Hund's rule? | Hund's rule of maximum spin multiplicity: electron pairing will not take place in a set of degenerate orbitals until first each orbital has been singly filled with parallel spin. This minimises electron repulsion |
| What are the names of the 'blocks' on the periodic table and why? | Groups 1 and 2 = s block. Groups 3-8 = p block. Transition metals = d block. Lanthanide and actinide series = f block. The electron configuration of an element ends with the orbital with the letter of the block. |
| Draw the electron configuration for carbon and calcium | Carbon: 1s2,2s2,2p2. Calcium: 1s2,2s2,2p6,3s2,3p6, 4s2 |
| What is the electron configuration of chlorine in terms of a noble gas? | [Ne]3s2,3p5 |
| What are the exceptions to the aufbau principle? | Chromium (24 e-): 1s22s22p63s23p63d54s1 instead of 1s22s22p63s23p63d44s2. Copper (29 e-): 1s22s22p63s23p63d104s1 instead of 1s22s22p63s23p63d94s2. It is more favourable to have a half/completely full set of d orbitals than a full set of s orbitals |
| What is a mole? | The mass of an element equal to its RAM in grams, so contains 6.02x10^23 atoms (Avogadro's number) |
| Define atomic number | The number of protons in an atom of an element, equal to the number of electrons |
| Define mass number | The number of protons plus neutrons in an atom of an element |
| What is an isotope? | Atoms of a single element with different numbers of neutrons so different mass numbers. |
| Define relative atomic mass | The average weighted mass of an atom of an element divided by 1/12th the mass of a C-12 atom |
| Define relative molecular mass | The weighted mass of a molecule divided by 1/12th the mass of a C-12 atom |
| Define relative isotopic mass | The weighted mass of an isotope divided by 1/12th the mass of a C-12 atom. Not an average! |
| What is mass spectrometry? | A method of finding the mass of atoms or groups of atoms so is used to determine relative atomic masses and relative molecular masses |
| Explain the steps in mass spectrometry | Sample is vaporised, atoms are ionised by being bombarded with high energy electrons, ions accelerated in electric field, deflected in magnetic field by electromagnet, series of paths dependent on mass/charge ratio, focused onto detector forming spectrum |
| To what extent are different ions deflected by the magnetic field? | High mass/charge ratio (large ions) are deflected less. Low mass/charge ratio (small ions) are deflected more. |
| What are the uses of mass spectrometry? | Measure metabolic gas exchange during surgery, sports testing for anabolic steroids in urine/blood, forensic analysis of blood/DNA, space research (mars, titan), pharmaceuticals content of drugs, carbon dating (ratio of C-12:C-14 in a sample, half life) |
| What is ionisation energy? | The energy required to remove an electron from an atom, ion or molecule - units are kJ/mol |
| What is first ionisation energy? | The energy required to remove one electron from the ground state of each atom in one mole of gaseous, neutral atoms of that element. A (g) -> A+ (g) + e- |
| What is second ionisation energy? | The energy required to remove one electron from each ion in one mole of gaseous, positive, singly charged ions of that element. A+ (g) -> A2+ (g) + e- |
| Is ionisation energy exothermic or endothermic and why? | Endothermic - energy has to be put in to remove an electron. |
| What evidence is there for principal energy levels? | Successive ionisation energies - second and third ionisation energies are higher than first - in a cation electrons move towards nucleus due to fewer number of electrons but same nuclear charge, so force of attraction is greater. |
| How do you calculate the group number from a graph of successive ionisation energies? | The number of successive ionisation energies before the first sudden change is the group number because it is the number of electrons in the outer shell. |
| What does a large jump in successive ionisation energies mean? | It means that the next energy level has been broken into, because there is a change in shielding and distance from nucleus. |
| What factors affect ionisation energies? | Amount of shielding, distance between outer electrons and nucleus, nuclear charge, effective nuclear charge, single/ paired electron (paired electrons require less energy to remove as 2 electrons in the same orbital experience repulsion) |
| What happens to ionisation energies as you go down a group? | Decreases down a group - atoms get larger so greater distance between outer electrons and nucleus, increased shielding - smaller force of attraction, easier to remove - outweighs increase in nuclear charge |
| What happens to ionisation energies as you go along a period? | Increases - electrons enter same principal energy level so little change in distance from nucleus or shielding - increase in nuclear and effective nuclear charge, so increased force of attraction. |
| What are the specific changes in ionisation energies as you go from group to group along a period? | 1-2: incr- higher nuclear + effective nuclear charge, same distance + shielding. 2-3: decr- p subshell further from nucleus, more shielding. 3-4/4-5: incr- same subshell. 5-6: decr- 1st electron pairing repulsion. 6-7/7-8: incr- same subshell.8-1 decrease |
| What evidence is there for subshells? | 2,3,3 pattern of ionisation energies along a period shows that there are subshells - if all electrons had the same energy, then ionisation energy would steadily increase as atomic number increased |
| What is periodicity? | The repeating pattern of a property e.g. ionisation energies, melting points |
| What is first electron affinity? | The energy change when one electron is added to each atom of one mole of neutral, gaseous atoms of that element. A (g) + e- -> A- (g). |
| What is second electron affinity? | The energy change when one electron is added to each ion in one mole of gaseous, singly charged, negative ions of that element. A- (g) + e- -> A2- (g) |
| Is electron affinity endo or exothermic? | First electron affinity is exothermic as there is a force of attraction between the electron being added and the nucleus. Second /third etc electron affinity is endothermic as energy has to be put in to overcome repulsion between electrons |
| How does atomic radius change down a group? | Increases due to more electrons so more principal energy levels |
| How does atomic radius change along a period? | Decreases due to increasing nuclear charge and there is little change in distance from nucleus (all electrons enter same principal energy level) or shielding so there is an increase in effective nuclear charge, so more attraction. |
| How does melting point change along a period? | 1-3: increase - more valence electrons, higher charge, smaller radius, stronger metallic bonding. 3-4: increase - giant covalent substance with strong covalent bonds extending over billions of atoms in a lattice |
| Continued | 4-7: decrease - simple molecular covalent substances have weak intermolecular forces, gaseous. In period 3, there is a slight increase between P (exists as p4) and S (exists as S8). 7-8 decrease - monatomic noble gases have weak intermolecular forces |
| How does melting point change down a group? | Decreases down groups 1+2 - same number of valence electrons, same charge on cations, but increasing metallic radius causing lower force of attraction |
| What are valence electrons? | Electrons that are free for bonding, such as those in the in outer shell |
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